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[UNITED STATES CONSULAR REPORTS. SPECIAL ISSUE NO. 10.]



SULPHUR MINES IN SICILY.

BY PHILLIP CARROLL, U. S. CONSUL, PALERMO.

Sulphur, or brimstone, is a hard, brittle substance of various colors, from brilliant yellow to dark brown, without smell when cool, of a mild taste, and burns with a pale blue flame, emitting pungent and suffocating fumes. Its specific gravity is from 1.9 to 2.1.

Sulphur exists more or less in all known countries, but the island of Sicily, it is thought, is the only place where it is produced on a large scale, and consequently that island appears to command the market. Small quantities have been found in the north of Italy, the Grecian Archipelago, Russia, Austria, Poland, France, Spain, eastern shores of Egypt, Tunis, Iceland, Brazil, Central America, and the United States. Large quantities are said to exist in various countries of Asia, but it is understood to be impracticable to utilize the same, consequent upon the distance from any commercial port and the absence of rail or other roads.

Sulphur is of two kinds, one of which is of volcanic emanation, the other being closely allied to sedimentary rocks. The latter is found in Sicily, on the southern and central portions of the island. Mount Etna, situated in the east, seems to exert no influence in the formation of brimstone. There are various hypotheses relative to its natural formation. Dr. Philip Swarzenburg attributes it to the emanations of sulphur vapor expelled from metallic matter existing in the earth, consequent upon the fire in the latter, while Professors Hoffman and Bischoff ascribe it to the decomposition of sulphureted hydrogen. Hoffman believes the sulphureted hydrogen must have passed through the fissures of stratified rocks, but Bischoff is of opinion that the sulphureted hydrogen must have been the result of the decomposition of sulphate of lime in the presence of organic matter. The theory of others is that sulphur owes its origin to the combination of lacustrine deposits with vegetable matter, and others again suppose that it is due to the action of the sea upon animal remains. The huge banks of rock salt often met with in the vicinity of sulphur mines, and which in some places stretch for a distance of several miles, seem to indicate that the sea has worked its way into the subsoil. Fish and insects, which are frequently found in strata of tripoli, which lie under sulphur beds, induce the belief that lakes formerly existed in Sicily.

The following is a list of the various strata which form part of the crust of the earth in Sicily, according to Professor Mottura, an Italian geologist:

Pliocene.—Sandstone; coarse calcareous rock; marl.

Upper Miocene.—Calcareous marl; gypsum, etc.; sulphur embedded in calcareous limestone; silicious limestone; tripoli, containing fossils of fish, insects' eggs, etc.

Middle Miocene.—Sandstone containing quartz, intercalated with marl of a saltish taste.

Lower Miocene.—Rock salt; blue marl, containing petroleum and bitumen; flintstone; ferruginous clay, mixed with aragonite and bituminous schists; ferruginous and silicious sandstone.

Eocene.—Limestone, containing diaspores and shells.

At times one or another of the strata disappears, while the order of some is slightly reversed on account of the broken state of the crust. Upon the whole, however, the above has been generally observed in the various mines by the author referred to.

Sulphur mines have been operated in Sicily over three hundred years, but until the year 1820 its exportation was confined to narrow limits. At present the number of mines existing in Sicily is about three hundred, nearly two hundred of which, being operated on credit, are, it is understood, destined to an early demise. It is said that there are about 30,000,000 tons of sulphur in Sicily at present, and that the annual production amounts to about 400,000 tons. If this should be true, taking the foregoing as a basis, the supply will become exhausted in about seventy-five years.

In 1819 a law was passed in Italy, which is still in force, governing mining in Sicily, which provides that should a land owner discover ore in his property he would be the owner thereof, and should have the right to mine, operate, or rent the property to others for that purpose, but if he should decline to operate his mines or to rent them to others to be operated, the state would rent them on its own account.

Royalties vary from 12 to 45 per cent. They are paid according to the quality of the ore and the facilities for producing sulphur; 25 per cent. may, however, be taken as an average. There is a land tax of 36 per cent. of the net income, which is usually paid by the owners and lessees of the mines, in proportion to the quantity of sulphur which they produce. The export duty is 10 lire per ton. All mines are inspected by government officials once a year, and the owners are required to furnish the state with plans of the works and their progress, with a view to insure the safety of the workmen and to ascertain the extent of the property.

Those who rent their mines receive from 10 to 40 per cent. of the sulphur produced. Leases are valid for such period as the contracting parties may stipulate therein. The general limit, however, is nine years. The average lease is 25 per cent., 40 per cent. being paid only when the mines are very favorably situated and the production good. Some lessees prefer paying a considerable sum in cash in advance, at the beginning of the term of the lease, and giving 15 or 20 per cent. in sulphur annually thereafter, instead of a higher percentage.

The external indications of the presence of sulphur are the appearance of gypsum and sulphurous springs. These are indubitable signs of the presence of sulphur, and when discovered the process resorted to here, in order to reach the sulphur, is to bore a hole sufficiently large to admit a man, after which steps are constructed in the passage in order to facilitate the workmen in going to and fro. These steps extend across the passage, and are about 25 centimeters high and 35 broad. The inclination of the holes or passages varies from 30 to 50 degrees. Upon attaining the depth of several meters water is often met with, and in such considerable quantity that it is impossible to proceed. Hence it becomes necessary to either pump the water out or retreat in order to bore elsewhere. It is often necessary to bore several passages in order to discover the ore or seam of sulphur. When, however, it has been discovered the passages are made to follow its direction, whether upward or downward. As the direction of seams is in most cases irregular, that of the passages or galleries is likewise. Where the ore is rich and the matrix yielding, the miners break it by means of pick-axes and pikes, but when such is not the case gunpowder is resorted to, the ore in this case being carried to the surface by boys. The miners detach the ore from the surrounding material, and the cavities which ensue in consequence assume the appearance of vast caves, which are here and there supported by pillars of rock and ore in order to keep them from falling or giving way. In order to strengthen the galleries sterile rock is piled upon each side and cemented with gypsum. In extensive mines, however, these supports and linings are too weak, and not infrequently, as a result, the galleries and caverns give way, occasionally causing considerable havoc among the miners. Sulphur is found from the surface to a depth of 150 meters. The difficulties met with in operating mines are numerous, and among the greatest in this category are water, land slides, irregularity of seam, deleterious gases, hardness of rocks and matrices. Of these difficulties, water is the most frequently met with. Indeed, it is always present, and renders the constant use of pumps necessary. At one time miners were allowed to dig where they pleased so long as sulphur was extracted, the consequence being that in groups of mines, the extent and direction of which being unknown to their respective owners, one mine often fell into or upon another, thus causing destruction to life and property. It was largely for this reason, it is understood, that the government determined to require owners and lessees of mines to furnish plans thereof to proper authority, and directed that official inspection of the mines should be made at stated periods. In order to comply with the decree of the government it became necessary to employ mining engineers to draw the plans, etc., and those employed were generally foreigners. In the system of excavation described no steam power is employed. Pumping is performed by means of primitive wooden hand pumps, and when sufficient ore has been collected it is conveyed on the backs of boys to the surface—a slow, costly, and difficult procedure. This system may, however, be suitable to small mines, but in large mines there is no economy in hand labor; indeed, much is lost in time and expense by it. For this reason steam has been introduced into the larger and more important mines. The machinery employed is a hoisting apparatus, with a drum, around which a coil is wound, with the object of hoisting and lowering trucks in vertical shafts. Steam pumps serve to extract the water. The force of the hoisting apparatus varies from 15 to 50 horse power. The fuel consumed is English and French coal, the former being preferred, as it engenders greater heat. The cost of a ton of coal at the wharf is $4.40, whereas in the interior of the island it costs about $10. The shafts or pits are made in the ordinary way, great care being taken in lining them with masonry in order to guard against land slides. In level portions of the country vertical shafts are preferred, but where the mine is situated upon a hill a debouch may often be found below the sulphur seam, when an inclined plane is preferred, the ore being placed in trucks and allowed to run down the plane on rails until it reaches the exterior of the mine, where it suddenly and violently stops, and as a result the trucks are emptied of their load, when they are drawn up the plane to be refilled; and thus the process goes on indefinitely. In these mines a gutter is made in the inclined plane which carries off the water, thus dispensing with the necessity of a pump and the requisites to operate it. The galleries and inclined shafts are lined with beams of pine or larch, which are brought hither from Sardinia, as Sicily possesses very little timber. The mines are illuminated by means of iron oil lamps, the wicks of which are exposed. The lamps are imported from Germany. In certain cases an earthenware lamp, made on the island, and said to be a facsimile of those used by the Phoenicians, is employed. This lamp is made in the shape of a small bowl. It is filled with oil and a wick inserted, which hangs or extends outward, and is thus ignited, the flame being exposed to the air. Safety lamps are unknown, and those described are generally secure. Few explosions take place—only when confined carbonic hydrogen is met with in considerable quantities, and when the ventilation is not good. In this case the mine is easily ignited, and once on fire may burn for years. The only practical expedient for extinguishing the fire is to close all inlets and outlets in order to shut off the air. This, however, is difficult and takes time. Notwithstanding the closing of communications, the gases escape through the fissures and openings which obtain everywhere, and the ingress of air makes it next to impossible to extinguish the fire; hence it burns indefinitely or until the mine is exhausted. Occasionally the burning of a mine results beneficially to its owners, in that it dispenses with the necessity of smelting, and produces natural, refined sulphur.

Galleries in extent are usually 1.20 by 1.80 meters, and when ore is not found and it becomes necessary to extend the galleries, laborers are paid in accordance with the progress they may make and the character of the rock, earth, etc., through which it may be necessary to cut, as follows:

Silicious limestone, 60 lire per meter; daily progress, 0.20 meter.

Gypsum, 50 lire per meter; daily progress, 0.30 meter.

Marl, 30 lire per meter; daily progress, 0.50 meter.

Clay, 15 lire per meter; daily progress, 1 meter.

Laborers working in the ore are paid 4.30 lire per ton. This includes digging, extracting, and illumination. In some mines, however, the laborers are paid when the sulphur is fused and ready for exportation. One ton of sulphur, or its equivalent (say from 40 to 50 lire), is the amount generally paid. In mines where this system obtains the administration is only responsible for their maintenance. Each miner produces on an average about 11/2 tons of ore daily, and when the works are not more than 40 meters in depth he employs one boy to assist him, two boys when they reach 60 meters, and three when under 100 meters. These boys are from seven to sixteen years of age, and are paid from 0.85 to 1.50 lire per day by the miner who employs them. They carry from 1,000 to 1,500 pounds of ore daily, or in from six to eight hours. The food consumed by miners is very meager, and consists of bread, oil, wine, or water; occasionally cheese, macaroni, and vegetables are added to the above.

Mining laborers generally can neither read nor write, and when employed in mines distant from habitations or towns, live and sleep therein, or in the open air, depending on the season or the weather. In a few mines the laborers are, however, provided with suitable dwelling places, and a relief fund is in existence for the succor of the families of those who die in the service. This fund is greatly opposed by the miners, from whose wages from 1 to 2 per cent. is deducted for its maintenance. In the absence of a fund of this character, the sick or infirm are abandoned by their companions and left to die. Generally miners are inoffensive when fairly dealt with. They are said to be indolent and dishonest as a rule. The managers of mines receive from 3,000 to 5,000 lire per annum; chief miners from 1,500 to 2,500 lire; surveyors, 700 to 1,000 lire; and weighers and clerks, from 1,000 to 2,000 lire per annum. The total number of mining laborers in Sicily is estimated at about 25,000.

The ore for fusion of the first grade as to yield contains from 20 to 25 per cent. of sulphur, that of the second grade from 15 to 20 per cent., and of the third grade 10 to 15 per cent. The usual means adopted for extracting sulphur from the ore is heat, which attains the height of 400 degrees Centigrade, smelting with the kiln, which in Sicilian dialect is called a "calcarone." The "calcarone" is capable of smelting several thousand tons of ore at a time and is operated in the open air. Part of the sulphur is burned in the process of smelting in order to liquefy the remainder. "Calcaroni" are situated as closely to the mouth of a shaft as possible, and if practicable on the side of a hill, in order that when the process of smelting is complete, the sulphur may run down the hill in channels prepared for the purpose. The shop of a "calcarone" is circular and the floor has an inclination of from 10 to 15 degrees. A design of a "calcarone" is herewith inclosed. The circular wall is made of rude stone work, cemented together with gypsum. The thickness of the wall at the back is 0.50 meter, and from this it gradually becomes thicker until in front, where it is 1 meter, when the diameter is to be 10 meters. In front of the thickest part of the wall an opening is left, measuring 1.20 meters high and 0.25 meter broad.

Through this opening the liquid sulphur flows. Upon each side of this opening two walls are built at right angles with the circular wall, in order to strengthen the front of the kiln. These walls are 80 centimeters thick each and are roofed. A door is hinged to these walls, thus forming a small room in front of each kiln in which the keeper thereof resides from the commencement to the termination of the flow of sulphur. The inclined floor of the kiln is made of stone work and is covered with "ginesi," the name given to the refuse of a former process of smelting. The stone work is 20 centimeters thick, and the "ginesi" covering 25 centimeters, which gradually becomes thicker as it approaches its lowest extremity. The front part of the circular wall is 3.50 meters high and the back 1.80 meters. The interior of the wall is plastered with gypsum in order to render it impermeable.

The cost of a "calcarone" of about 500 tons capacity is 800 lire. The capacity varies from 40 to 5,000 tons, or more, depending upon circumstances. If a mine is enabled to smelt the whole year round, the smaller "calcaroni," being more easily managed, are preferred; the inverse is the case as to the larger "calcaroni," when this is impracticable. When a "calcarone" is situated within 100 meters of a cereal farm, its operation is prohibited by law during the summer, lest the fumes of the sulphur should destroy the crop.

When, however, the distance is greater from the farm or farms than 100 meters, smelting is permitted; but should any damage ensue to the crops as a result of the fumes, the owners of the "calcaroni" are required to liquidate it. Therefore the mines which are favorably situated smelt the entire year, and employ "calcaroni" of from 40 to 500 tons, as there is less risk of a process failing, which occasionally happens, and for the reason that the ore can be smelted as soon as it is extracted; whereas, when kilns or "calcaroni" are situated within or adjacent to the limit adverted to, they can only be operated five or six months in the year, consequent upon which the ore is necessarily stacked up all through the summer or until such time as smelting may be commenced without endangering the crops, when it becomes necessary to use "calcaroni" whose capacity amounts to several thousand tons. As intimated, these large "calcaroni" are not so manageable as those of smaller dimensions, and as a result many thousands of tons of sulphur are lost in the process of smelting, besides perhaps the loss of an entire year in labor. Again, the ore deteriorates or depreciates when long exposed to the air and rain, all of which, when practicable, render the kilns or "calcaroni" of the smaller capacity more advantageous and lucrative to those operating sulphur mines in Sicily. Smelting with a "calcarone" of 200 tons capacity consumes thirty days, one of 800 tons 60 days, and with a "calcarone" of 2,000 tons capacity from 90 to 120 days are consumed.

In loading or filling the "calcaroni," the larger blocks of ore are placed at the bottom as well as against the mouth, in order to keep the lower part of the kiln as cool as possible with a view of preventing the liquid sulphur from becoming ignited as it passes down to where it makes its exit, etc. The blocks of ore thus first placed in position are, for obvious reasons, the most sterile. After the foundation is thoroughly laid the building of the "pile" is proceeded with, the larger blocks being placed in the center to form, as it were, the backbone of the pile; the smaller blocks of ore are arranged on the outside of these and in the interstices. The shape or form of the pile when completed is similar to a truncated cone, and when burning the kiln looks like a small volcano. When the kiln has been filled with ore, the whole is covered with ginesi with a view of preventing the escape of the fumes. The ore is then ignited by means of bundles of straw, impregnated or saturated with sulphur, being held above the thin portion of the top of the kiln, which is at once closed with ginesi, and the "calcarone" is left to itself for about a week. During the burning process the flames gradually descend, and the sulphur contained in the ore is melted by the heat from above. In about seven or eight days sulphuric fumes and sublimed sulphur commence to escape, when it becomes necessary to add a new coat of ginesi to the covering and thus prevent the destruction of vegetation by the sulphur fumes. The mouth of the kiln, which has been left open in order to create a draught, is closed up about this time with gypsum plaster. When the sulphur is all liquefied it finds its way to the most depressed part of the kiln, and there, upon encountering the large sterile blocks, quite cold, already referred to, solidifies. It is again liquefied by means of burning straw, whereupon an iron trough is inserted into a mouth made in the kiln for the purpose, and the reliquefied sulphur runs into it, from which it is immediately collected into wooden moulds, called "gadite," and which have been kept cool by being submerged in water. Upon its becoming thoroughly cool the sulphur is taken out of the moulds referred to, and is now in solid blocks, each weighing about 100 weight. Two of these blocks constitute a load for a mule, and cost from 4 to 5 francs.

The above is the result when the operation succeeds; but this is not always the case. At times the sulphur becomes solidified before it reaches the mouth of the kiln, because of the heat not being sufficient to keep it liquid in its passage thereto, and other misfortunes not within control, and consequent upon the use of the larger kilns, or "calcaroni."

When the sulphur ceases to run from the kiln, the process is complete. The residue is left to cool, which consumes from one to two months. The cooling process could be accomplished in much less time by permitting the air to enter the kiln, but this would be destructive to vegetation, and even to life, consequent upon the fumes of the sulphur. The greatest heat at a given time in a kiln is calculated to be above 650 degrees Centigrade—that is, at the close of the process. This enormous heat is generally allowed to waste, whereas it is understood it could be utilized in many ways. A gentleman of the name of Gill is understood to have invented a recuperative kiln, which will, if generally adopted, utilize the heat of former processes named. A ton of ore containing about 25 per cent. of sulphur yields 300 pounds of sulphur. This is considered a good yield. When it yields 200 pounds it is considered medium, and poor when only 75 pounds. Laborers are paid 0.40 lire per ton for loading and unloading kilns, and from thirty to forty hands are employed at a time. The keeper of a kiln receives from 2 to 2.50 lire per day.

Notwithstanding the "calcarone" has many defects, it is the simplest and cheapest mode of smelting, and is preferred here to any other system requiring machinery and skilled labor to operate it.

The following are the principal furnaces in use here: Durand's; Hirzel; Gill and Kayser's system of fusion; Conby Bollman process; Thomas steam process of smelting; and Robert Gill's recuperative kilns.

There are seven qualities or grades of sulphur, viz.:

1. Sulphur almost chemically pure, of a very bright and yellow color.

Second Best.—Slightly inferior to the first quality; bright and yellow.

Second Good.—Contains 4 to 5 per cent. of earthy matter, but is of a bright yellow.

Second Current.—Dirty yellow, containing more earthy matter than that last named.

Third Best.—Brownish yellow; this tint depends on the amount of bitumen which it contains.

Third Good.—Light brown, containing much extraneous matter.

Third Current.—Brown and coarse.

These qualities are decided by color, not by test. The difference of price is from 3 to 10 francs per ton. Manufacturers prefer the third best, because of its containing more sulphuric acid and costing less than the sulphur of better quality.

Sulphur is conveyed to the seaboard by rail, in carts, or on mules or donkeys. Conveyance by cart, mule, or donkey is only resorted to when the distance is short or from mines to railroad stations. The tariff in the latter case is understood to be 1 lire per ton per mile. The railroad tariff is 0.12 per ton per kilometer; but it is contemplated, it is understood, to reduce this to 7 centimes in a short time. The price per ton of sulphur is as follows:

At Porto At At Grade. Empedocle. Licata. Catania. Lire. Lire. Lire. Second best 86.60 87.00 90.70 Second good 84.42 84.50 90.30 Second current 83.90 83.90 88.40 Third best 79.00 79.90 86.90 Third good 77.80 77.80 83.00 Third current 76.80 76.70

Sulphur free on board, brokerage, shipment, export duty, and all other expenses included, costs 20 lire per ton in excess of the above prices. Nearly all the sulphur exported from Palermo emanates from the Lercara mines, in the province of Palermo, the price per ton being as follows: first quality, 91.60 lire; second quality, 88.40. Sulphur is usually conveyed in steamers to foreign countries from Sicilian ports. The average freight per ton to New York is about as follows: From Palermo, 8.70 lire; from Catania, 13.50 lire; from Girgenti, 16 lire. An additional charge of 2.50 lire is made when the sulphur may be destined for other ports in the United States.

Liebig once said that the degree of civilization of a nation and its wealth could be seen in its consumption of sulphuric acid. Now, although Italy produces immense quantities of sulphur, it cannot, on account of the scarcity of fuel, and other obvious reasons perhaps, compete with certain other countries in the manufacture and consumption of sulphuric acid.

Sulphur is employed in the manufacture of sulphuric acid, and the latter serves in the manufacture of sulphate of soda, chloridic acid, carbonate of soda, azodic acid, ether, stearine candles, purification of oils in connection with precious metals and electric batteries. Nordhausen's sulphuric acid is employed in the manufacture of indigo. Sulphate of soda is employed in the manufacture of artificial soda, glassware, cold mixtures, and medicines. Carbonate of soda is used in the manufacture of soap, bleaching wool, coloring and painting tissues, and in the manufacture of fine crystal ware and the preparation of borax. Chloric acid is used in the preparation of chlorides with bioxide of manganese, and with chlorides in the preparation of hypochlorides of lime, known in commerce under the name of bleaching powder, and improperly called chloride of lime, which is used as a disinfectant in contagious diseases, in bleaching stuffs, and in the manufacture of paper from vegetable fibers, and in the manufacture of gelatine extracted from bones, as well as in fermenting molasses and in the manufacture of sugar from beet root. Sulphur is also used in the preparation of gunpowder and oil of vitriol, and in the manufacture of matches and cultivation of the vine.

In the year 1838 the Neapolitan government granted a monopoly to a French company for the trade in sulphur. By the terms of the agreement the producers were required to sell their sulphur to the company at certain fixed prices, and the latter paid the government the sum of $350,000 annually in consideration of this requirement. This, however, was not a success, and tended to curtail the sulphur industry, and the government, discovering the agreement to be against its interests, annulled it, and established a free system of production, charging an export tax per ton only. At that time sulphuric acid was derived exclusively from sulphur. Hence the demand from all countries was great, and the prices paid for sulphur were high. It was about this period that the sulphur industry was at its zenith. The monopoly having been abolished, every mine did its utmost to produce as much sulphur as possible, and from the export duty exacted by the government there accrued to it a much larger revenue than that which it received during the period of the monopoly. The progress of science has, however, modified the state of things since then, as sulphur can now be obtained from pyrite or pyrite of iron. This discovery immediately caused the price of sulphur to fall, and the great demand therefore correspondingly ceased. In England, at the present time, it is understood that two-thirds of the sulphuric acid used is manufactured from pyrites. The decrease in prices caused many of the mines to suspend operations, and as a result the sulphur remained idle in stock. In 1884 an association was formed at Catania with a view to buying up sulphur thus stored away at the mines and various ports at low prices, and store it away until a favorable opportunity should present itself for the sale thereof. This had the effect of increasing the prices of sulphur in Sicily for some time, and the producers, discovering that the methods of the association increased the foreign demand for their produce as well as its prices, exported it directly themselves, thus breaking up the association referred to, as it was no longer a profitable concern.

The railroad system, which in later years has placed the most important parts of Sicily in communication with the seaboard, has been most beneficial to the sulphur industry. A great saving has been made in transporting it to the ports. This was formerly (as stated) accomplished by carts drawn by mules at an enormous expense, as the roads were wretched, and unless some person of distinction contemplated passing over them, repairs were unknown.

Palermo, March 20, 1888.

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AN AUTOMATIC STILL.

BY T. MABEN.

The arrangement here described is one that may readily be adapted to, and is specially suited for, the old fashioned stills which are in frequent use among pharmacists for the purpose of distilling water. The idea is extremely simple, but I can testify to its thorough efficiency in actual practice. The still is of tinned copper, two gallon capacity, and the condenser is the usual worm surrounded with cold water.

The overflow of warm water from the condenser is not run into the waste pipe as in the ordinary course, but carried by means of a bent tube, A, B, C, to the supply pipe of the still. The bend at B acts as a trap, which prevents the escape of steam.



The advantages of this arrangement are obvious. It is perfectly simple, and can be adapted at no expense. It permits of a continuous supply of hot water to the still, so that the contents of the latter may always be kept boiling rapidly, and as a consequence it condenses the maximum amount of water with the minimum of loss of heat. If the supply of water at D be carefully regulated, it will be found that a continuous current will be passing into the still at a temperature of about 180 deg. F., or, if practice suggest the desirability of running in the water at intervals, this can be easily arranged. It is necessary that the level at A should be two inches or thereabout higher than the level of the bend at C, otherwise there may not be sufficient head to force a free current of water against the pressure of steam. It will also be found that the still should only contain water to the extent of about one-fourth of its capacity when distillation is commenced, as the water in the condenser becomes heated much more rapidly than the same volume is vaporized. By this expedient a still of two gallons capacity will yield about half a dozen gallons per day, a much greater quantity than could ever be obtained under the old system, which required the still to be recharged with cold water every time one and a half gallons had been taken off.

The objection to all such continuous or automatic arrangements is, of course, that the condensed water contains all the free ammonia that may have existed in the water originally, but it is only in cases where the water is exceptionally impure that this disadvantage will become really serious. The method here outlined has, no doubt, occurred to many, and may probably be in regular use, but not having seen any previous mention of the idea, I have thought that it might be useful to some pharmacists who prepare their own distilled water.—Phar. Jour.

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COTTON SEED OIL.

"Cotton seed oil," said Mr. A.E. Thornton, of the Atlanta mills, "is one of the most valuable of oils because it is a neutral oil, that is, neither acid nor alkali, and can be made to form the body of any other oil. It assimilates the properties of the oil with which it is mixed. For instance, olive oil. Cotton seed oil is taken and a little extract of olives put in. The cotton oil takes up the properties of the extract, and for all practical purposes it is every bit as good as the pure olive oil. Then it is used in sweet oil, hair oil, and, in fact, in nearly all others. A chemist cannot tell the prepared cotton oil from olive oil except by exposing a saucerful of each, and the olive oil becomes rancid much quicker than the cotton oil. The crude oil is worth thirty cents a gallon, and even as it is makes the finest of cooking lard, and enters into the composition of nearly all lard."

A visit to the mills showed how the oil is made. From the platform where the seed is unloaded it is thrown into an elevator and carried by a conveyor—an endless screw in a trough—to the warehouse. Then it is distributed by the conveyor uniformly over the length of the building—about 200 feet. The warehouse is nearly half filled now, and thousands and thousands of bushels are lying in store. Another elevator carries the seed up to the "sand screen." This is a revolving cylinder made of wire cloth, the meshes being small enough to retain the seed, which are inside the cylinder, but the sand and dirt escape. Now the seeds start down an inclined trough. There is something else to be taken out, and that is the screws and nails and rocks that were too large to be sifted out with the sand and dirt. There is a hole in the inclined trough, and up through that hole is blown a current of air by a suction fan. If it were not for the fan, the cotton seed, rocks, nails, and all would fall through. The current keeps up the cotton seed, and they go on over, but it is not strong enough to keep up the nails and pebbles, and they fall through. Now the seed, free of all else, is carried by another elevator and endless screw conveyor to the "linter." This is really nothing more than a cotton gin with an automatic feed.

"HULLER" AND "HEATERS."

Then the seed is carried to the "huller," where it is crushed or ground into a rough meal about as coarse as the ordinary corn "grits." The next step is to separate the hulls from the kernels, all the oil being in the kernel, so the crushed seed is carried to the "separator." This is very much on the style of a sand screen, being a revolving cylinder of wire cloth. The kernels, being smaller than the broken hulls, fall through the broken meshes, and upon this principle the hull is separated and carried direct to the furnace to be used as fuel. The kernels are ground as fine as meal, very much as grist is ground, between corrugated steel "rollers," and the damp, reddish colored meal is carried to the "heater."

The "heater" is one iron kettle within another, the six inch steam space between the kettles being connected direct with the boilers. There are four of these kettles side by side. The meal is brought into this room by an elevator, the first "heater" is filled, and for twenty minutes the meal is subjected to a "dry cook," a steam cook, the steam in the packet being under a pressure of forty-five pounds. Inside the inner kettle is a "stirrer," a revolving arm attached at right angles to a vertical shaft. The stirrer makes the heating uniform, and the high temperature drives off all the water in the meal, while the involatile oil all remains.

In five minutes the next heater is filled, in five minutes the next, etc.

Now there are four "heaters," and as the last heater is filled—at the end of twenty minutes—the first heater is emptied. Then at the end of five minutes the first heater is filled, and the one next to it is emptied, and the rotation is kept up, each heater full of meal being "dry-cooked" for twenty minutes.

Corresponding to the four heaters are four presses. Each press consists of six iron pans, shaped like baking pans, arranged one above the other, and about five inches apart. The pans are shallow, and around the edge of each is a semicircular trough, and at the lowest point of the trough is a funnel-shaped hole to enable the oil to run from one pan to the next lowest, and from the lowest pan to the "receiving tanks" below.

PRESSING OUT THE OIL.

As soon as a "heater" is ready to be emptied, the meal is taken out and put into six hair sacks, corresponding to the six pans in the press. There are six hair mats about one foot wide and six long, one side of each being coated with leather. The hair mat is about an inch thick. Now the hair sack, containing ten and a half to eleven pounds of heated steaming meal, is placed on one end of the mat, and the meal distributed so as to make a pad or cushion of uniform thickness. The pad of meal is not quite three feet long, a foot wide, and three inches thick, and the hair mat is folded over, sandwiching the pad and leaving the leather coating of the pad outside. In this form the six loads are put into the six pans, and by means of a powerful hydraulic press the pans are slowly pressed together. The oil begins trickling out at the side, slowly at first, and then suddenly it begins running freely. The pressure on the "loads" is 350 tons. After being pressed about five minutes, the pressure is eased off and the "loads" taken out. What had been a mushy pad three inches thick is a hard, compact cake about three-quarters of an inch thick, and the sack is literally glued to the cake. The crude oil has a reddish muddy color as it runs into the tanks.

To one side were lying great heaps of sacks of yellowish meal—the cakes which have been broken and ground up into meal. That, as explained above, forms the body of all fertilizers. The following is a summary of the work for the eight months' season at the Atlanta mills:

Fifteen thousand tons of seed used give:

Fifteen million pounds of hull.

Ten million three hundred and thirty-one thousand two hundred and fifty pounds of meal.

Four million six hundred and sixty-eight thousand seven hundred and fifty pounds of oil.

Three hundred thousand pounds of lint cotton.

The meal is worth at the rate of $6 for 700 pounds, or $88,603.58.

The oil is worth thirty cents a gallon, or seven and a half pounds, or $186,750.

The lint is worth $18,000, making a total of $293,353, and that doesn't include the 15,000,000 pounds of hull.—Atlanta Constitution.

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MANUFACTURE OF PHOTOGRAPHIC SENSITIVE PLATES.

Quite recently Messrs. Marion & Company, London, began on their own account to manufacture sensitive photographic plates by machinery, and the operations are exceedingly delicate, for a single minute air bubble or speck of dust on a plate may mar the perfection of a picture. Their works for the purpose at Southgate were erected in the summer of 1886, and were designed throughout by Mr. Alexander Cowan.



Buildings of this kind have to be specially constructed, because some of the operations have to be carried on in the absence of daylight, and in that kind of non-actinic illumination which does not act upon the particular description of sensitive photographic compound manipulated. Glass and other materials have therefore to pass from light to dark rooms through double doors or double sliding cupboards made for the purpose, and the workshops have to be so placed in relation to each other that the amount of lifting and the distance of carriage of material shall be reduced to a minimum. Moreover, the final drying of sensitive photographic plates takes place in absolute darkness. Fig. 1 is a ground plan of the chief portion of the works. In this cut, A is the manager's private office, B the counting house, C the manager's laboratory, and D his dark room for private experiment, which can thus be conducted without interfering with the regular work of the establishment. E is the carpenter's shop and packing room, F the albumen preparation room, G the engine room, with its two doors; the position of the engine is marked at H. The main building is entered through the door, K; the passage, L, is used for the storage of glass, and has openings in the wall on one side to permit the passage of glass into the cleaning room, M; this room is illuminated by daylight. The plates, after being cleaned, pass into the coating rooms, N and O, into which daylight is never admitted; the coating machine is in the room, N, and three hand coating tables in the room, O; both these rooms are illuminated by non-actinic light.



The walls of N and O are of brick, to keep these interior rooms as cool as possible in hot weather, for the making of photographic plates is more difficult in summer time, because the high temperature tends to prevent the rapid setting of the gelatine emulsion upon them. At the end of these rooms and communicating with both is the lift, P, by which the coated plates are carried to the drying rooms above, which there cover the entire area of the main building; they consist of two rooms measuring 60 ft. by 30 ft., and are each 30 ft. high at the highest part in the center of the building; these rooms are necessarily kept in absolute darkness, except while the plates are being stored therein or removed therefrom, and on such occasions non-actinic light is used. After the plates are dry, they come down the lift, Q, into the cutting and packing room, R, which is illuminated by non-actinic light. In the drying rooms the batches of plates are placed one after the other on tram lines at one end of the room, and are gradually pushed to the other end of the building, so that the first batches coated are the first to be ready to be taken off when dry, and to be sent down the lift, Q. The plates in R, when sufficiently packed to be safe from the action of daylight, are passed through specially constructed openings into the outside packing room, S, where they are labeled. The chemicals are kept in the room, U, where they are weighed and measured ready for the making of the photographic emulsion in the room, U. The next room, V, is for washing small experimental batches of emulsion, and W is the large washing room. The emulsion is then taken into the passage, X, communicating with the two coating rooms. A centrifugal machine in the room, Y, is used for extracting silver residues from waste materials, also for freeing the emulsion from all soluble salts. Washing and cleaning in general go on in the room, Z.



The glass for machine coating is cut to standard sizes at the starting, instead of being coated in large sheets and cut afterward—a practice somewhat common in this industry. The disadvantage of the ordinary plan is that minute fragments of glass are liable to settle upon the sensitive film and to cause spots and scratches during the packing operations; any defect of this kind renders a plate worthless to the photographer. When any breakages take place in the cutting, it is best that they should occur at the outset, and not after the plate has been coated with emulsion. The cutting when necessary is effected by the aid of a "cutting board," Fig. 2, invented by Mr. Cowan, and now largely in use in the photographic world. This appliance is used to divide into two equal parts, with absolute exactness, any plate within its capacity, and it is especially useful in dimly lighted rooms. It consists of four rods pivoted together at the corners and swinging on two centers, so that in the first position it is truly square, and in other positions of rhomboid form, the two outer bars approaching each other like those of a parallel ruler. The hinge flap comes down on the exact center of the plate, minus the thickness of the block holding the diamond. By this appliance plates can be cut in either direction. Fig. 3 represents a similar arrangement for cutting a number of very small plates out of one large one; in this the hinge flap is made in the form of a gridiron, and the bars are spaced at accurate distances, according to the size of the plate to be cut, so that a plate 10 in. square, receiving four cuts in each direction, will be divided into twenty-five small plates.



Before being cleaned all sharp edges are roughly taken off those plates intended for machine coating by girls, who rub the edges and corners of the plates upon a stone; the plates are then cleaned by any suitable method in use among photographers. The plates, now ready for the coating room, have to be warmed to the temperature of the emulsion, say from 80 deg. F. to 100 deg. F., before they pass to the coating machine, the inventor of which, Mr. Cadett, having come to the conclusion that, if the plates are not of the proper temperature, the coating given will be uneven over various parts of the surface. The plate-warming machine is represented in Fig. 4; it was designed by Mr. A. Cowan, and made by his son, Mr. A. R. Cowan. It consists of a trough 7 ft. long by 3 in. deep, forming a flat tank, through which hot water passes by means of the circulating system shown in the engraving. To facilitate the traveling of the glass plates without friction the top of the tank is a sheet of plate glass bedded on a sand bath. An assistant at one end places the glasses one after the other on the warm glass slab, and by means of a movable slide pushes them one at a time under the cover, which cover is represented raised in the engraving to show the interior of the machine. After having put one glass plate on the slide, another cannot be added until the man in the dark room at the other end of the slide has taken off the farthest warmed plate, because the slide has a reciprocating movement. This heating apparatus is built at right angles to the coating machine in the next room, in order to be conveniently placed in the present building; but it is intended in future to use it as a part of the coating machine itself, and to drive it at the same speed and with the same gearing, so that the cold plates will be put on by hand at one end, get warmed as they pass into the dark room, at the other end of which they will be delivered by the machine in coated condition. Underneath the heating table is a copper boiler, with its Bunsen's burner of three concentric rings to get up the temperature quickly and to give the power of keeping the water under the heating slab at a definite temperature, as indicated by a thermometer. The cold water tank of the system is represented against the wall in the cut.



Fig. 5 represents the hot water circulating system outside the coating rooms for keeping the gelatine emulsions in these dimly lighted regions at a given temperature, without liberating the products of combustion where the emulsion is manipulated. The temperature is regulated automatically. It will be noticed where the pipes enter the two coating rooms, and Fig. 6 shows the copper inside one of them heated by the apparatus just described. The emulsion vessel in the copper is surrounded by warm water, and the copper itself is jacketed and connected with the hot water pipes, so forming part of the circulating system.



Fig. 7 is a general view of the coating machine recently invented by Mr. Cadett, of the Greville Works, Ashtead, Surrey. The plates warmed in the light room, as already described, are delivered near the end of the coating table, where they are picked off a gridiron-like platform, represented on the right hand side of the cut, and are placed by an assistant one by one upon the parallel gauges shown at the beginning of the machine proper; they are then carried on endless cords under the coating trough described farther on. After they have been coated they are carried onward upon a series of four broad endless bands of absorbent cotton—Turkish toweling answers well—and this cotton is kept constantly soaked with cold water, which flows over sheets of accurately leveled plate glass below and in contact with the toweling; the backs of the plates being thus kept in contact with fresh cold water, the emulsion upon them is soon cooled down and is firmly set by the time the plates have reached the end of the series of four wet tables. They are then received upon one over which dry toweling travels, which absorbs most of the moisture which may be clinging to the backs of the plates; very little wet comes off the backs, so that during a day's work it is not necessary to adopt special means to redry this last endless band. What are technically known as "whole plates," which are 81/2 in. by 61/2 in., are placed touching each other end to end as they enter the machine, and they travel through it at the rate of 720 per hour; smaller sizes are coated in proportion, the smaller the plates the larger is the number coated in a given time. The smaller plates pass through the machine in two parallel rows, instead of in a single row, so that quarter plates, 41/4 in. by 31/4 in., are delivered at the end of the machine at the rate of 2,800 per hour, keeping two attendants well employed in picking them up and placing them in racks as quickly as they can do the work. The double row of cords for carrying two lines of small plates through the machine is represented in the engraving. Although the plates touch each other at their edges on entering the machine, they are separated from each other by short intervals after being coated; this is effected by differential gearing. The water flowing over the tables for cooling the plates is caught in receptacles below and carried away by pipes. Between each of the tables is a little roller to enable small plates to travel without tilting over the necessary gap between each pair of bands.



The feeding trough of Cadett's machine is represented in Fig. 8. The plates, cleaned as already described, are carried upon the cords under a brass roller, the weight of which causes sufficient friction to keep the plates from tilting; they next pass under a soft camel's hair brush to remove anything in the shape of dust or grit, and are then coated. They afterward pass over a series of accurately leveled wheels running in a tank of water kept exact by an automatic regulator at a temperature of from 80 deg. Fah. to 100 deg. Fah., by means of a small hot water circulating system. The emulsion trough is jacketed with hot water at a constant temperature. This trough is silver plated inside, because most metals in common use would spoil the emulsion by chemical action. The trough is 16 in. long; it somewhat tapers toward the bottom, and contains a series of silver pumps shown in the cut; the whole of this series of pumps is connected with one long adjustable crank when plates of the largest size have to be coated; when coating plates of smaller sizes some of the pumps are detached. A chief object of the machine is to deliver a carefully measured quantity of emulsion upon each plate, and this is done by means of pumps, in order that the quantity of emulsion delivered shall not be affected by changes in the level of the emulsion in the trough; the quantity delivered is thus independent of variations due to gravity or to the speed of the machine. These pumps draw the emulsion from a sufficient depth in the trough to avoid danger from the presence of air bubbles, and the bottom of the trough is so shaped that should by chance any sedimentary matter be present, it has a tendency to travel downward, away from the bottoms of the pumps. There is a steady flow of emulsion from the pumps to the delivery pipes, then it passes down a guide plate of the exact width of the plate to be coated. Immediately in front of the guide plate is a fixed silver cylinder, kept out of contact with the plate by the thickness of a piece of fine and very hard hempen cord, which can be renewed from time to time. These cords keep the cylinder from scraping the emulsion off the plate, and they help to distribute it in an even layer. There would be two lines upon each plate where it is touched by the cords, were not the emulsion so fluid as to flow over the cut-like lines made and close them up.



The silver cylinder to a certain extent overcomes the effects of irregularities in the glass plates, for the cylinder is jointed somewhat in the cup and ball fashion, and is made in two or more parts, which parts are held together by lengths of India rubber.

The arrangement is shown in section in Fig. 9, in which A is the hot water jacket of the emulsion vessel; B, the crank driving the pumps; C, a pump with piston in position; D, delivery tube of the pump; E, the silver guide plate to conduct the emulsion down to the glass; F, the spreading cylinder; G, the cords regulating the distance of the cylinder from the glass plates; H, soft camel's hair brush; K, friction roller; L L L, three plates passing under the emulsion tank; M, knife edged wheels in the hot water tank, N; the "plucking roller," P, has a hot water tank of its own, and travels at slightly greater speed than the other rollers; R is the beginning of the cooling bands; T, the driving cords; and W, a level of the emulsion in the trough. Y represents one of the bucket pistons of the pumps, detached. The construction of the crank itself is such that, by adjustment of the connecting rods, more or less emulsion may be put upon the plates. Mr. Cowan, however, intends to adjust the pumps once for all, and to regulate the amount of emulsion delivered upon the plates by means of driving wheels of different diameters upon the cranks.



Fig. 10 is a section of the hollow spreading cylinder, made of sheet silver as thin as paper, so that its weight is light. For coating large plates it is divided in the center, so as to adapt itself somewhat to irregularities in the surface of each plate. In this case it is supported by a third and central thread, as represented in the cut. Otherwise the cylinder would touch the center of the plate. Its two halves are held together by a slip of India rubber.—The Engineer.

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THE USE OF AMMONIA AS A REFRIGERATING AGENT.[1]

[Footnote 1: Paper lately read before the Civil and Mechanical Engineers' Society.]

BY MR. T.B. LIGHTFOOT, M.I.C.E.

Within the last few years considerable progress has been made in the application of refrigerating processes to industrial purposes, and the demand for refrigerating apparatus thus created has led to the production of machines employing various substances as the refrigerating agent. In a paper read by the author before the Institution of Mechanical Engineers, in May, 1886, these systems were shortly described, and general comparisons given as to their respective merits, scope of application, and cost of working. In the present paper it is proposed to deal entirely with the use of ammonia as a refrigerating agent, and to deal with it in a more full and comprehensive manner than was possible in a paper devoted to the consideration of a number of different systems and apparatus. In the United States and in Germany, as well as to some extent elsewhere, ammonia has been very generally employed for refrigerating purposes during the last ten years or so. In this country, however, its application has been extremely limited; and even at the present time there are but few ammonia machines successfully at work in Great Britain. No doubt this is, to a large extent, due to the fact that in the United States and in Germany there existed certain stimulating causes, both as regards climate and manufactures, while in this country, on the other hand, these causes were present only in a modified degree, or were absent altogether. The consequence was that up to a comparatively recent date the only machine manufactured on anything like a commercial scale was the original Harrison's ether machine, first produced by Siebe, about the year 1857—a machine which, though answering its purpose as a refrigerator, was both costly to make and costly to work. In 1878 the desirability of supplementing our then existing meat supply by means of the large stocks in our colonies and abroad led to the rapid development of the special class of refrigerating apparatus commonly known as the dry air refrigerator, which, in the first instance, was specially designed for use on board ship, where it was considered undesirable to employ chemical refrigerants. Owing to their simplicity, and perhaps also to their novelty, these cold air machines have very frequently been applied on land, under circumstances in which the same result could have been obtained with much greater economy by the use of ammonia or some other chemical agent. Recently, however, more attention has been directed to the question of economy, and consideration is now being given to the applicability of certain machines to certain special purposes, with the result that ammonia—which is the agent that, in our present state of knowledge, gives as a rule the best results for large installations, while on land at any rate its application for all refrigerating purposes presents no unusual difficulties—promises to become largely adopted. It is hoped, therefore, that the following paper respecting its use will be of interest.

In all cases where a liquid is employed, the refrigerating action is produced by the change in physical state from the liquid to the vaporous form. It is, of course, well known that such a change can only be brought about by the acquirement of heat; and for the purpose of refrigeration (by which must be understood the abstraction of heat at temperatures below the normal) it is obvious that, other things being equal, that liquid is the best which has the highest heat of vaporization, because with it the least quantity has to be dealt with in order to produce a given result. In fact, however, liquids vary, not only in the amount of heat required to vaporize them (this amount also varying according to the temperature or pressure at which vaporization occurs), but also in the conditions under which such change can be effected. For instance, water has an extremely high latent heat, but as its boiling point at atmospheric pressure is also high, evaporation at such temperatures as would enable it to be used for refrigerating purposes can only be effected under an almost perfect vacuum. The boiling point of anhydrous ammonia, on the other hand, is 371/2 deg. below zero F. at atmospheric pressure, and therefore for all ordinary cooling purposes its evaporation can take place at pressures considerably above that of our atmosphere. Some other agents used for refrigerating purposes are methylic ether, Pictet's liquid, sulphur dioxide, and ether. In this connection it should be stated that Pictet's liquid is a compound of carbon dioxide and sulphur dioxide, and is said to possess the property of having vapor tensions not only much below those of pure carbon dioxide at equal temperatures, but even below those of pure sulphur dioxide at temperatures above 78 deg. F. The considerations, therefore, which chiefly influence the selection of a liquid refrigerating agent are:

1. The amount of heat required to effect the change from the liquid to the vaporous state, commonly called the latent heat of vaporization.

2. The temperatures and pressures at which such change can be effected.

This latter attribute is of twofold importance; for, in order to avoid the renewal of the agent, it is necessary to deprive it of the heat acquired during vaporization, under such conditions as will cause it to assume the liquid form, and thus become again available for refrigeration. As this rejection of heat can only take place if the temperature of the vapor is somewhat above that of the cooling body which receives the heat, and which, for obvious reasons, is in all cases water, the liquefying pressure at the temperature of the cooling water, and the facility with which this pressure can be reached and maintained, is of great importance in the practical working of any refrigerating apparatus. Ammonia in its anhydrous form, the use of which is specially dealt with in this paper, is a liquid having at atmospheric pressure a latent heat of vaporization of 900, and a boiling point at the same pressure of 371/2 deg. below zero F. Water being unity, the specific gravity of the liquid at a temperature of 40 deg. F. is 0.76, and the specific gravity of its vapor is 0.59, air being unity. In the use of ammonia, two distinct systems are employed. So far, however, as the mere evaporating or refrigerating part of the process is concerned, it is the same in both. The object is to evaporate the liquid anhydrous ammonia at such tension and in such quantity as will produce the required cooling effect. The actual tension under which this evaporation should be effected in any particular case depends entirely upon the temperature at which the acquirement of heat is to take place, or, in other words, on the temperature of the material to be cooled. The higher the temperature, the higher may be the evaporating pressure, and therefore the higher is the density of the vapor, the greater the weight of liquid evaporated in a given time, and the greater the amount of heat abstracted. On the other hand, it must be remembered that, as in the case of water, the lower the temperature of the evaporating liquid, the higher is the heat of vaporization. It is in the method of securing the rejection of heat during condensation of the vapor that the two systems diverge, and it will be convenient to consider each of these separately.

The Absorption Process.—The principle employed in this process is physical rather than mechanical. Ordinary ammonia liquor of commerce of 0.880 specific gravity, which contains about 38 per cent. by weight of pure ammonia and 62 per cent. of water, is introduced into a vessel named the generator. This vessel is heated by means of steam circulating through coils of iron piping, and a mixed vapor of ammonia and water is driven off. This mixed vapor is then passed into a second vessel, in order to be subjected to the cooling action of water. And here, owing to the difference between the boiling points of water and ammonia, fractional condensation takes place, the bulk of the water, which condenses first, being caught and run back to the generator, while the ammonia in a nearly anhydrous state is condensed and collected in the lower part of the vessel.

This process of fractional condensation is due to Rees Reece, and forms an important feature in the modern absorption machine. Prior to the introduction of this invention, the water evaporated in the generator was condensed with the ammonia, and interfered very seriously with the efficiency of the process by reducing the power of the refrigerating agent by raising its boiling point. In the improved form of apparatus, ammonia is obtained in a nearly anhydrous condition, and in this state passes on to the refrigerator. In this vessel, which is in communication with another vessel called the absorber, containing cold water or very weak ammonia liquor, evaporation takes place, owing to the readiness with which cold water or weak liquor absorbs the ammonia, water at 59 deg. Fahr. absorbing 727 times its volume of ammonia vapor. The heat necessary to effect this vaporization is abstracted from brine or other liquid, which is circulated through the refrigerator by means of a pump. Owing to the absorption of ammonia, the weak liquor in the absorber becomes strengthened, and it is then pumped back into the generating vessel to be again dealt with as above described.

The absorption apparatus, as applied for cooling purposes, consists of a generator, which is a vessel of cast iron containing coils of iron piping to which steam at any convenient pressure is supplied; an analyzer, in which a portion of the water vapor is condensed, and from which it flows back immediately into the generator; a rectifier and condenser, in the upper portion of which a further condensation of water vapor and a little ammonia takes place, the liquid thus formed passing back by a pipe to the analyzer and thence to the generator, while in the lower portion the ammonia vapor is condensed and collected; and a refrigerator or cooler, into which the nearly anhydrous liquid obtained in the condenser is admitted by a pipe and regulating valve, and allowed to evaporate, the upper portion being in communication with the absorber.

Through this vessel weak liquor, which has been deprived of its ammonia in the generator, is continually circulated, after being first cooled in an economizer by an opposite current of strong cold liquor passing from the absorber to the generator, while, in addition, the liquor in the absorber, which would become heated by the liberation of heat due to the absorption and consequent liquefaction of the ammonia vapor, is still further cooled by the circulation of cold water. As the pressure in the absorber is much lower than that in the generator, the strong liquor has to be pumped into the latter vessel, and for this purpose pumps are provided. Though of necessity the various operations have been described separately, the process is a continuous one, strong liquor from the absorber being constantly pumped into the generator through the heater or economizer, while nearly anhydrous liquid ammonia is being continually formed in the condenser, then evaporated in the refrigerator and absorbed by the cool weak liquor passing through the absorber.

Putting aside the effect of losses from radiation, etc., all the heat expended in the generator will be taken up by the water passing through the condenser, less that portion due to the condensation of the water vapor in the analyzer, and plus the amount due to the difference between the temperature of the liquid as it enters the generator and the temperature at which it leaves the condenser. In the refrigerator the liquid ammonia, in becoming vaporized, will take up the precise quantity of heat that was given off during its cooling and liquefaction in the condenser, plus the amount due to the difference in heat of vaporization, owing to the lower pressure at which the change of state takes place in the refrigerator, and less the small amount due to the difference in temperature between the vapor entering the condenser and that leaving the refrigerator, less also the amount necessary to cool the liquid ammonia to the refrigerator temperature. When the vapor enters into solution with the weak liquor in the absorber, the heat taken up in the refrigerator is imparted to the cooling water, subject also to corrections for differences of pressure and temperature. The sources of loss in such an apparatus are:

a. Radiation and conduction of heat from all vessels and pipes above normal temperature, which can, to a large extent, be prevented by lagging.

b. Conduction of heat from without into all vessels and pipes that are below normal temperature, which can also to a large extent be prevented by lagging.

c. Inefficiency of economizer, by reason of which heat obtained by the expenditure of steam in the generator is passed on to the absorber and there uselessly imparted to the cooling water.

d. The entrance of water into the refrigerator, due to the liquid being not perfectly anhydrous.

e. The useless evaporation of water in the generator. With regard to the amount of heat used, it will have been seen that the whole of that required to vaporize the ammonia, and whatever water vapor passes off from the generator, has to be supplied from without. Owing to the fact that the heating takes place by means of coils, the steam passed through may be condensed, and thus each pound can be made to give up some 950 units of heat. With the absorption process worked by an efficient boiler, it may be taken that 200,000 thermal units per hour may be eliminated by the consumption of about 100 lb. of coal per hour, with a brine temperature in the refrigerator of about 20 deg. Fahr.

Compression Process.—In this process ammonia is used in its anhydrous form. So far as the action of the refrigerator is concerned, it is precisely the same as it is in the case of the absorption apparatus, but instead of the vapor being liquefied by absorption by water, it is drawn from the refrigerator by a pump, by means of which it is compressed and delivered into the condenser at such pressure as to cause its liquefaction at the temperature of the cooling water. It must be borne in mind, however, that allowance must be made for the rise of temperature of the water passing through the condenser, and also for the difference in temperature necessary in order to permit the transfer of heat from one side of the cooling surface to the other. In a compression machine the work applied to the pump may be accounted for as follows:

a. Friction.

b. Heat rejected during compression and discharge.

c. Heat acquired by the ammonia in passing through the pump.

d. Work expended in discharging the compressed vapor from the pump.

But against this must be set the useful mechanical work performed by the vapor entering the pump. The heat rejected in the condenser is the heat of vaporization taken up in the refrigerator, less the amount due to the higher pressure at which the change in physical state occurs, plus the heat acquired in the pump, and less the amount due to the difference between the temperature at which the vapor is liquefied in the condenser and that at which it entered the pump. An ammonia compression machine, as applied to ice making, contains ice-making tanks, in which is circulated a brine mixture, uncongealable at any temperature likely to be reached during the process. This brine also circulates around coils of wrought iron pipes, in which the liquid ammonia passing from the condenser is vaporized, the heat required for this vaporization being obtained from the brine. A pump draws off the ammonia vapor from the refrigerator coils, and compresses it into the condenser, where, by means of the combined action of pressure and cooling by water, it assumes a liquid form, and is ready to be again passed on to the refrigerator for evaporation. The ammonia compression process is more economical than the absorption process, and with a good boiler and engine about 240,000 thermal units per hour can be eliminated by the expenditure of 100 lb. of coal per hour, with a brine temperature in the refrigerator of about 20 deg. Fahr.

GENERAL CONSIDERATIONS.

From what has been said, it will have been seen that, so far as the mere application is concerned, there is no difference whatever between the absorption and compression processes. The following considerations, therefore, which chiefly relate to the application of refrigerating apparatus, will be dealt with quite independent of either system. The application of refrigerating apparatus may roughly be divided into the following heads:

a. Ice making.

b. The cooling of liquids.

c. The cooling of stores and rooms.

Ice Making.—For this purpose two methods are employed, known as the can and cell systems respectively. In the former, moulds of tinned sheet copper or galvanized steel of the desired size are filled with the water to be frozen, and suspended in a tank through which brine cooled to a low temperature in the refrigerator is circulated. As soon as the water is completely frozen, the moulds are removed, and dipped for a long time into warm water, which loosens the blocks of ice and enables them to be turned out. The thickness of the blocks exercises an important influence upon the number of moulds required for a given output, as a block 9 in. thick will take four or five times as long to freeze solid as one of only 3 in. In the cell system a series of cellular walls of wrought or cast iron are placed in a tank, the distance between each pair of walls being from 12 to 16 in., according to the thickness of the block required. This space is filled with the water to be frozen. Cold brine circulates through the cells, and the ice forms on the outer surfaces, gradually increasing in thickness until the two opposite layers meet and join together. If thinner blocks are required, the freezing process may be stopped at any time and the ice removed. In order to detach the ice it is customary to cut off the supply of cold brine and circulate brine at a higher temperature through the cells. Ice frozen by either of the above described methods from ordinary water is more or less opaque, owing to the air liberated during the freezing process, little bubbles of which are caught in the ice as it forms, and in order to produce transparent ice it is necessary that the water should be agitated during the freezing process in such a way as to permit the air bubbles to escape. With the can system this is generally accomplished by means of arms having a vertical or horizontal movement. These arms are either withdrawn as the ice forms, leaving the block solid, or they are made to work backward and forward in the center of the moulds, dividing the block vertically into two pieces. With the cell system agitation is generally effected by making a communication between the bottom of each water space and a chamber below, in which a paddle or wood piston is caused to reciprocate. The movement thus given to the water in the chamber is communicated to that in the process of being frozen, and the small bubbles of air are in this way detached and set free. The ice which first forms on the sides of the moulds or cells is, as a rule, sufficiently transparent even without agitation. The opacity increases toward the center, where the opposing layers join, and it is, therefore, more necessary to agitate toward the end of the freezing process than at the commencement. As the capacity for holding air in solution decreases if the temperature of the water is raised, less agitation is needed in hot than in temperate climates. Experiments have been made from time to time with the view of producing transparent ice from distilled water, and so dispensing with agitation. In this case the cost of distilling the water will have to be added to the ordinary working expenses.

Cooling of Liquids.—In breweries, distilleries, butter factories, and other places where it is desired to have a supply of water or brine for cooling and other purposes at a comparatively low temperature, refrigerating machines may be advantageously applied. In this case the liquid is passed through the refrigerator and then utilized in any convenient manner.

Cooling of Rooms.—For this purpose the usual plan is to employ a circulation of cold brine through rows of iron piping, placed either on the ceiling or on the walls of the rooms to be cooled. In this, as in the other cases where brine is used, it is employed merely as a medium for taking up heat at one place and transferring it to the ammonia in the refrigerator, the ammonia in turn completing the operation by giving up the heat to the cooling water during liquefaction in the condenser. The brine pipes cool the adjacent air, which, in consequence of its greater specific gravity, descends, being replaced by warmer air, which in turn becomes cold, and so the process goes on. Assuming the air to be sufficiently saturated, which is generally the case, some of the moisture in it is condensed and frozen on the surface of the pipes; and if the air is renewed in whole or in part from the outside, or if the contents of the chamber are wet, the deposit of ice in the pipes will in time become so thick as to necessitate its being thawed off. This is accomplished by turning a current of warm brine through the pipes. Another method has been proposed, in which the brine pipes are placed in a separate compartment, air being circulated through this compartment to the rooms, and back again to the cooling pipes in a closed cycle by means of a fan. This plan was tried on a large scale by Mr. Chambers at the Victoria Docks, but for some reason or other was abandoned. One difficulty is the collection of ice from the moisture deposited from the air, which clogs up the spaces between the pipes, besides diminishing their cooling power. This, in some cases, can be partially obviated by using the same air over again, but in most instances special means would have to be provided for frequent thawing off, the pipes having, on account of economy of space and convenience, to be placed so close together, and to be so confined in surface, that they are much more liable to have their action interfered with than when placed on the roof or walls of the room.

In addition to the foregoing there are, of course, many other applications of ammonia refrigerating machines of a more or less special nature, of which time will not permit even a passing reference. Many of these are embraced in the second class, cold water or brine being used for the cooling of candles, the separation of paraffin, the crystallization of salts, and for many other purposes. In the same way cold brine has been used with great success for freezing quicksand in the sinking of shafts, the excavation being carried out and the watertight tubing or lining put in while the material is in a solid state. In a paper such as this it would be quite impracticable to enter into details of construction, and the author has therefore confined himself chiefly to principles of working. In conclusion, however, it may be added that in ammonia machines, whether on the absorption or compression systems, no copper or alloy of copper can be used in parts subjected to the action of the ammonia. Cast or wrought iron and steel may, however, be used, provided the quality is good, but special care must be taken in the construction of those parts of absorption machines which are subjected to a high temperature. In both classes of apparatus first-class materials and workmanship are most absolute essentials.

* * * * *

[Continued from Supplement, No. 646, p. 10319.]



ELEMENTS OF ARCHITECTURAL DESIGN.[1]

[Footnote 1: Delivered before the Society of Arts, London, December 13, 1887. From the Journal of the Society.]

BY H. H. STATHAM.

III.—CONTINUED.

The Romans, in their arched constructions, habitually strengthened the point against which the vault thrust by adding columnar features to the walls, as shown in Fig. 108; thus again making a false use of the column in a way in which it was never contemplated by those who originally developed its form. In Romanesque architecture the column was no longer used for this purpose; its place was taken by a flat pilaster-like projection of the wall (plan and section, Fig. 109), which gave sufficient strength for the not very ambitious vaulted roofs of this period, where often in fact only the aisles were vaulted, and the center compartment covered with a wooden roof. At first this pilaster-like form bore a reminiscence of a classic capital as its termination; a moulded capping under the eaves of the building. Next this capping was almost insensibly dropped, and the buttress became a mere flat strip of wall. As the vaulting became bolder and more ambitious, the buttress had to be made more massive and of greater projection, to afford sufficient abutment to the vault, more especially toward the lower part, where the thrust of the roof is carried to the ground. Hence arose the tendency to increase the projection of the buttress gradually downward, and this was done by successive slopes or "set-offs," as they are termed, which assisted (whether intentionally or not in the first instance) in further aiding the correct architectural expression of the buttress. Then the vaulting of the center aisle was carried so high and treated in so bold a manner, with a progressive diminution of the wall piers (as the taste for large traceried windows developed more and more), that a flying buttress (see section, Fig. 110) was necessary to take the thrust across to the exterior buttresses, and these again, under this additional stress, were further increased in projection, and were at the same time made narrower (to allow for all the window space that was wanted between them), until the result was that the masses of wall, which in the Romanesque building were placed longitudinally and parallel to the axis of the building, have all turned about (Fig. 110, plan) and placed themselves with their edges to the building to resist the thrust of the roofing. The same amount of wall is there as in the Romanesque building, but it is arranged in quite a new manner, in order to meet the new constructive conditions of the complete Gothic building.



It will be seen thus how completely this important and characteristic feature of Gothic architecture, the buttress, is the outcome of practical conditions of construction. It is treated decoratively, but it is itself a necessary engineering expedient in the construction. The application of the same principle, and its effect upon architectural expression, may be seen in some other examples besides that of the buttress in its usual shape and position. The whole arrangement and disposition of an arched building is affected by the necessity of providing counterforts to resist the thrust of arches. The position of the central tower, for instance, in so many cathedrals and churches, at the intersection of the nave and transepts, is not only the result of a feeling for architectural effect and the centralizing of the composition, it is the position in which also the tower has the cross walls of nave and transepts abutting against it in all four directions: if the tower is to be placed over the central roof at all, it could only be over this point of the plan. In the Norman buildings, which in some respects were finer constructions than those of later Gothic, the desire to provide a firm abutment for the arches carrying the tower had a most marked effect on the architectural expression of the interior. At Tewkesbury, for instance, while the lower piers are designed in the usual way toward the north and south sides (viz., as portions of a pier of nearly square proportion standing under the angle of the tower), in the east and west direction the tower piers run out into great solid masses of wall, in order to insure a sufficient abutment for the tower arches. On the north and south sides the solid transept walls were available immediately on the other side of the low arch of the side aisle, but on the east and west sides there were only the nave and choir arcades to take the thrust of the north and south tower arches, and so the Normans took care to interpose a massive piece of wall between, in order that the thrust of the tower arches might be neutralized before it could operate against the less solid arcaded portions of the walls. This expedient, this great mass of wall introduced solely for constructive reasons, adds greatly to the grandeur of the interior architectural effect. The true constructive and architectural perception of the Normans in this treatment of the lower piers is illustrated by the curious contrast presented at Salisbury. There the tower piers are rather small, the style is later, and the massive building of the Normans had given way to a more graceful but less monumental manner of building. Still the abutment of the tower arches was probably sufficient for the weight of the tower as at first built; but when the lofty spire was put on the top of this, its vertical weight, pressing upon the tower arches and increasing their horizontal thrust, actually thrust the nave and choir arcades out of the perpendicular toward the west and east respectively, and there they are leaning at a very perceptible angle away from the center of the church—the architectural expression, in a very significant form, of the neglect of balance of mass in construction.

But while the buttress in Gothic architecture has been in process of development, what has the vault been doing? We left it (Fig. 92) in the condition of a round wagon vault, intersected by another similar vault at right angles. By that method of treatment we got rid of the continuous thrust on the walls. But there were many difficulties to be faced in the construction of vaulting after this first step had been taken, difficulties which arose chiefly from the rigid and unmanageable proportions of the circular arch, and which could not be even partially solved till the introduction of the pointed arch. The pointed arch is the other most marked and characteristic feature of Gothic architecture, and, like the buttress, it will be seen that it arose entirely out of constructive difficulties.

These difficulties were of two kinds; the first arose from the tendency of the round arch, when on a large scale and heavily weighted, to sink at the crown if there is even any very slight settlement of the abutments. If we turn again to diagram 77, and observe the nearly vertical line formed there by the joints of the keystone, and if we suppose the scale of that arch very much increased without increasing the width of each voussoir, and suppose it built in two or three rings one over the other (which is really the constructive method of a Gothic arch), we shall see that these joints in the uppermost portion of the arch must in that case become still more nearly vertical; in other words, the voussoirs almost lose the wedge shape which is necessary to keep them in their places, and a very slight movement or settlement of the abutments is sufficient to make the arch stones lose some of their grip on each other and sink more or less, leaving the arch flat at the crown. There can be no doubt that it was the observance of this partial failure of the round arch (partly owing probably to their own careless way of preparing the foundations for their piers—for the mediaeval builders were very bad engineers in that respect) which induced the builders of the early transitional abbeys, such as Furness and Fountains and Kirkstall, to build the large arches of the nave pointed, though they still retain the circular-headed form for the smaller arches in the same buildings, which were not so constructively important. This is one of the constructive reasons which led to the adoption of the pointed arch in mediaeval architecture, and one which is easily stated and easily understood. The other influence is one arising out of the lengthened conflict with the practical difficulties of vaulting, and is a rather more complicated matter, which we must now endeavor to follow out.



Looking at Fig. 92, it will be seen that in addition to the perspective sketch of the intersecting arches, there is drawn under it a plan, which represents the four points of the abutment of the arches (identified in plan and perspective sketch as A, B, C, D), and the lines which are taken by the various arches shown by dotted lines. Looking at the perspective sketch, it will be apparent that the intersection of the two cross vaults produces two intersecting arches, the upper line of which is shown in the perspective sketch (marked e and f); underneath, this intersection of the two arches, which forms a furrow in the upper side of the construction, forms an edge which traverses the space occupied by the plan of the vaulting as two oblique arches, running from A to C and from B to D on the plan. Although these are only lines formed by the intersection of two cross arches, still they make decided arches to the eye, and form prominent lines in the system of vaulting; and in a later period of vaulting they were treated as prominent lines and strongly emphasized by mouldings; but in the Roman and early Romanesque vaults they were simply left as edges, the eye being directed rather to the vaulting surfaces than to the edges. The importance of this distinction between the vaulting surfaces and their meeting edges or groins[2] will be seen just now. The edges, nevertheless, as was observed, do form arches, and we have therefore a system of cross arches (A B and C D[3] Fig. 95), two wall arches (A, D and B C), and two oblique arches (A C and B D), which divide the space into four equal triangular portions; this kind of vaulting being hence called quadripartite vaulting. In this and the other diagrams of arches on this page, the cross arches are all shown in positive lines, and the oblique arches in dotted lines.

[Footnote 2: A groin is the edge line formed by the meeting and intersection of any two arched surfaces. When this edge line is covered and emphasized by a band of moulded stones forming an arch, as it were, on this edge, this is called a groin rib.]

[Footnote 3: The "D" seems to have been accidentally omitted in this diagram; it is of course the fourth angle of the plan.]

We have here a system in which four semicircular arches of the width of A B are combined with two oblique arches of the width of A C, springing from the same level and supposed to rise to the same height. But if we draw out the lines of these two arches in a comparative elevation, so as to compare their curves together, we at once find we are in a difficulty. The intersection of the two circular arches produces an ellipse with a very flat crown, and very liable to fail. If we attempt to make the oblique arch a segment only of a large circle, as in the dotted line at 94, so as to keep it the same level as the other without being so flat at the top, the crown of the arch is safer, but this can only be done at the cost of getting a queer twist in the line of the oblique arch, as shown at D, Fig. 93. The like result of a twist of the line of the oblique arch would occur if the two sides of the space we are vaulting over were of different lengths, i.e. if the vaulting space were otherwise than a square, as long as we are using circular arches. If we attempt to make the oblique arches complete circles, as at Fig. 96, we see that they must necessarily rise higher than the cross and side arches, so that the roof would be in a succession of domical forms, as at Fig. 97. There is the further expedient of "stilting" the cross arches, that is, making the real arch spring from a point above the impost and building the lower portion of it vertical, as shown in Fig. 98. This device of stilting the smaller arches to raise their crowns to the level of those of the larger arches was in constant use in Byzantine and early Romanesque architecture, in the kind of manner shown in the sketch, Fig. 99; and a very clumsy and makeshift method of dealing with the problem it is; but something of the kind was inevitable as long as nothing but the round arch was available for covering contiguous spaces of different widths. The whole of these difficulties were approximately got over in theory, and almost entirely in practice, by the adoption of the pointed arch. By its means, as will be seen in Fig. 100, arches over spaces of different widths could be carried to the same height, yet with little difference in their curves at the springing, and without the necessity of employing a dangerously flat elliptical form in the oblique arch. A sketch of the Gothic vault in this form, and as the intersection of the surfaces of pointed vaults, is shown in Fig. 101.

But now another and most important change was to come over the vault. The mediaeval architects were not satisfied with the mere edge left by the Romans in their vaults, and even before the full Gothic period the Roman builders had emphasized their oblique arches in many cases by ponderous courses of moulded or unmoulded stone in the form of vaulting ribs. These, in the case of Norman building, were probably not merely put for the purpose of architectural expression, but also because they afforded an opportunity of concealing behind the lines of a regularly curved groin rib the irregular curves which were really formed by the junction of the vaulting surfaces. But when the vault become more manageable in its curves after the adoption of the pointed arch, the groin rib became adopted in the early pointed vaulting as a means of giving expression and carrying up the lines of the architectural design. On its edge were stones moulded with the deep undercut hollows of early English moulding, defining the curves of the oblique as well as of the cross arches with strongly marked lines, and, moreover, falling on a level with each other in architectural importance; the oblique vault of the arch is no longer a secondary line in the vaulting design; on the contrary, the cross arches are usually omitted, as shown in Figs. 102 and 103 (view and plan of an early Gothic quadripartite vault); so that the cross rib, which, in the early Romanesque wagon vault (Fig. 90), was the one marked line on the vaulting surface, has now been obliterated, and the line of the oblique arch (E F, Figs. 102, 103) has taken its place.

The effect of the strongly marked lines of the groin ribs, radiating from the cap of the shaft which was their architectural support, seems to have been so far attractive to the mediaeval builders that they soon endeavored to improve upon it and carry it further by multiplying the groin ribs. One of the stages of this progress is shown in Figs. 104, 105. Here it will be seen that the cross rib is again shown, and that intermediate ribs have been introduced between it and the oblique rib. The richness of effect of the vault is much heightened thereby; but a very important modification in the mode of constructing it has been introduced. As the groin ribs become multiplied, it came to be seen that it was easier to construct them first, and fill in the spaces afterward; accordingly the groin, instead of being, as it was in the early days of vaulting, merely the line formed by the meeting of two arch surfaces, became a kind of stone scaffolding or frame work, between which the vaulting surfaces were filled in with lighter material. This arrangement of course made an immense difference in the whole principle of constructing the vault, and rendered it much more ductile in the hands of the builder, more capable of taking any form which he wished to impose on it, than when the vault was regarded and built as an intersection of surfaces. There was still one difficulty, however, one slight failure both practical and theoretical in the vault architecture, which for a long time much exercised the minds of the builders. The ribs of the vaulting being all of unequal length, they had to assume different curves almost immediately on rising from the impost; and as the mouldings of the ribs have to be run into each other ("mitered" is the technical term) on the impost, there not being room to receive them all separately, it was almost impossible to get them to make their divergence from each other in a completely symmetrical manner; the shorter ribs with the quicker curves parted from each other at a lower point than the larger ones, and the "miters" occurred at unequal heights. The effort to get over this unsatisfactory and irregular junction of the ribs at the springing was made first by setting back the feet of the shorter ribs on the impost capping, somewhat in the rear of the feet of the larger ribs, so as to throw their parting point higher up; but this also was only a makeshift, which it was hoped the eye would pass over; and in fact it is rarely noticeable except to those who know about it and look for it. Still the defect was there, and was not got over until the idea occurred of making all the ribs of the same curvature and the same length, and intercepting them all by a circle at the apex of the vault, as shown in Figs. 106, 107; the space between the circles at the apex of the vault being practically a nearly flat surface or plafond held in its place by the arches surrounding it; though, for effect, it is often treated otherwise in external appearance, being decorated by pendants giving a reversed curve at this point, but which of course are only ornamental features hung from the roof. If we look again at Fig. 104, we shall see that this was a very natural transition after all, for the arrangement of the ribs and vaulting surfaces in that example is manifestly suggestive of a form radiating round the central point of springing, though it only suggests that, and does not completely realize it. But here came a further and very curious change in the method of building the vault, for as the ribs were made more numerous, for richness of effect, in this form of vaulting, it was discovered that it was much easier to build the whole as a solid face of masonry, working the ribs on the face of it. Thus the ribs, which in the intermediate period were the constructive framework of the vault, in the final form of fan vaulting came back to their original use as merely a form of architectural expression, meant to carry on the architectural lines of the design; and they perform, on a larger scale and with a different expression, much the same kind of function which the fluting lines performed in the Greek column. The fan vault is therefore a kind of inverted dome, built up in courses on much the same principle as a dome, but a convex curve internally, instead of a concave one, the whole forming a series of inverted conoid forms abutting against the wall at the foot and against each other at their upper margins. This form of roof is wonderfully rich in effect, and has the appearance of being a piece of purely artistic work done for the pleasure of seeing it; yet, as we have seen, it is in reality, like almost everything good in architecture, the logical outcome of a contention with structural problems.