 |
SCIENTIFIC AMERICAN SUPPLEMENT NO. 822
NEW YORK, October 3, 1891
Scientific American Supplement. Vol. XXXII, No. 822.
Scientific American established 1845
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
* * * * *
TABLE OF CONTENTS.
I. ANTHROPOLOGY.—The Study of Mankind.—A review of Prof. Max Muller's recent address before the British Association. 13141
II. CHEMISTRY.—Standards and Methods for the Polarimetric Estimation of Sugars.—A U.S. internal revenue report on the titular subject.—2 illustrations. 13138
The Formation of Starch in Leaves.—An interesting examination into the physiological role of leaves.—1 illustration. 13138
The Water Molecule.—By A. GANSWINDT.—A very interesting contribution to structural chemistry. 13137
III. CIVIL ENGINEERING.—Demolition of Rocks under Water without Explosives.—Lobnitz System.—By EDWARD S. CRAWLEY.—A method of removing rocks by combined dredging and ramming as applied on the Suez Canal.—3 illustrations. 13128
IV. ELECTRICITY.—Electrical Standards.—The English Board of Trade commission's standards of electrical measurements. 13129
The London-Paris Telephone.—By W.H. PREECE, F.R.S.—Details of the telephone between London and Paris and its remarkable success.—6 illustrations. 13131
The Manufacture of Phosphorus by Electricity.—A new industry based on dynamic electricity.—Full details. 13132
The Two or Three Phase Alternating Current Systems.—By CARL HERING.—A new industrial development in electricity fully described and graphically developed.—15 illustrations. 13130
V. GEOGRAPHY AND EXPLORATION.—The Grand Falls of Labrador.—The Bowdoin College exploring expedition and its adventures and discoveries in Labrador. 13140
VI. MECHANICAL ENGINEERING.—Improved Changeable Speed Gearing.—An ingenious method of obtaining different speeds at will from a single driving shaft.—2 illustrations. 13129
Progress in Engineering.—Notes on the progress of the last decade. 13129
VII. MEDICINE AND HYGIENE.—Eyesight.—Its Care during Infancy and Youth.—By L. WEBSTER FOX, M.D.—A very timely article on the preservation of sight and its deterioration among civilized people. 13135
The Use of Compressed Air in Conjunction with Medicinal Solutions in the Treatment of Nervous and Mental Affections.—By J. LEONARD CORNING.—The enhancement of the effects of remedies by subsequent application of compressed air. 13134
VIII. MINERALOGY.—A Gem-Bearing Granite Vein in Western Connecticut.—By L.P. GRATACAP.—A most interesting mineral fissure yielding mica and gems recently opened. 13141
IX. NATURAL HISTORY.—Ants.—By RUTH WARD KAHN.—An interesting presentation of the economy of ants. 13140
X. NAVAL ENGINEERING.—Armor Plating on Battleships—France and Great Britain.—A comparison of the protective systems of the French and English navies.—5 illustrations. 13127
The Redoutable.—An important member of the French Mediterranean fleet described and illustrated.—1 illustration. 13127
XI. TECHNOLOGY.—New Bleaching Apparatus.—A newly invented apparatus for bleaching pulp.—2 illustrations. 13133
* * * * *
THE REDOUTABLE.
The central battery and barbette ship Redoutable, illustrated this week, forms part of the French Mediterranean squadron, and although launched as early as 1876 is still one of its most powerful ships. Below are some of the principal dimensions and particulars of this ironclad:
Length 318 ft. 2 in. Beam 64 " 8 " Draught 25 " 6 " Displacement 9200 tons. Crew 706 officers and men.
The Redoutable is built partly of iron and partly of steel and is similar in many respects to the ironclads Devastation and Courbet of the same fleet, although rather smaller. She is completely belted with 14 in. armor, with a 15 in. backing, and has the central battery armored with plates of 91/2 in. in thickness.
The engines are two in number, horizontal, and of the compound two cylinder type, developing a horse power of 6,071, which on the trial trip gave a speed of 14.66 knots per hour. Five hundred and ten tons of coal are carried in the bunkers, which at a speed of 10 knots should enable the ship to make a voyage of 2,800 knots. Torpedo defense netting is fitted, and there are three masts with military tops carrying Hotchkiss revolver machine guns.
The offensive power of the ship consists of seven breechloading rifled guns of 27 centimeters (10.63 in.), and weighing 24 tons each, six breechloading rifled guns of 14 centimeters (5.51 in.), and quick-firing and machine guns of the Hotchkiss systems. There are in addition four torpedo discharge tubes, two on each side of the ship. The positions of the guns are as follows: Four of 27 centimeters in the central battery, two on each broadside; three 27 centimeter guns on the upper deck in barbettes, one on each side amidships, and one aft. The 14 centimeter guns are in various positions on the broadsides, and the machine guns are fitted on deck, on the bridges, and in the military tops, four of them also being mounted on what is rather a novelty in naval construction, a gallery running round the outside of the funnel, which was fitted when the ship was under repairs some months ago.
There are three electric light projectors, one forward on the upper deck, one on the bridge just forward of the funnel, and one in the mizzen top.—Engineering.
* * * * *
ARMOR PLATING ON BATTLESHIPS: FRANCE AND GREAT BRITAIN.
The visit of the French squadron under Admiral Gervais to England has revived in many a nautical mind the recollection of that oft-repeated controversy as to the relative advantages of armored belts and citadels. Now that a typical French battleship of the belted class has been brought so prominently to our notice, it may not be considered an inappropriate season to dwell shortly upon the various idiosyncrasies of thought which have produced, in our two nations, types of war vessels differing so materially from each other as to their protective features. In order to facilitate a study of these features, the accompanying sketch has been prepared, which shows at a glance the relative quantities of armored surface that afford protection to the Nile, the Camperdown, the Marceau, the Royal Sovereign, and the Dupuy de Lome; the first three of these vessels having been actually present at the review on the 21st of August and the two others having been selected as the latest efforts of shipbuilding skill in France and Great Britain. Nothing but the armored surface in each several class is shown, the same scale having been adhered to in all cases.
Two impressions cannot fail to be made upon our minds, both as to French and British armor plate disposition. These two impressions, as regards Great Britain, point to the Royal Sovereign as embodying the idea of two protected stations with a narrow and partial connecting belt; and to the Nile as embodying the idea of a vast and absolutely protected raft. For France, we have the Marceau as representing the wholly belted type with four disconnected but protected stations; and the Dupuy de Lome, in which the armor plating is thinned out to a substance of only 4 in., so as entirely to cover the sides of the vessel down to 5 ft, below the water line; this thickness of plating being regarded as sufficient to break up upon its surface the dreaded melinite or guncotton shell, but permitting the passage of armor-piercing projectiles right through from side to side; provision being made to prevent damage from these latter to engines and vitals by means of double-armored decks below, with a belt of cellulose between them. Thus, as we have explained, two prominent ideas are present in the disposition of armor upon the battleships of Great Britain, as well as in that of the battleships of France. But, while in our country these two ideas follow one another in the natural sequence of development, from the Inflexible to the Royal Sovereign, the citadel being gradually extended into two redoubts, and space being left between the redoubts for an auxiliary battery—this latter being, however, singularly placed above the armored belt, and not within its shelter—in France, on the other hand, we find the second idea to be a new departure altogether in armored protection, or rather to be a return to the original thought which produced the Gloire and vessels of her class. In point of fact, while we have always clung to the armored citadel, France has discarded the belt altogether, and gone in for speed and light armor, as well as for a much lighter class of armament. Time alone, and the circumstances of actual warfare, can prove which nation has adopted the wisest alternative.
A glance at the engraving will show the striking contrast between the existing service types as to armored surface. The Marceau appears absolutely naked by the side of the solidly armed citadel of the Nile. The contrast between the future types will be, of course, still more striking, for the reasons given in the last paragraph. But while remarking upon the paucity of heavy plating as exhibited in the service French battleships, we would say one word for the angle at which it is placed. The receding sides of the great vessels of France give two very important attributes in their favor. In the first place, a much broader platform at the water line is afforded to secure steadiness of the ship and stable equilibrium, and the angle at which the armor rests is so great as to present a very oblique surface to the impact of projectiles. The trajectory of modern rifled guns is so exceedingly flat that the angle of descent of the shot or shell is practically nil. Were the sides of the Royal Sovereign to fall back like those of the Marceau or Magenta, we seriously doubt whether any projectile, however pointed, would effect penetration at all. We conclude, then, that a comparison of the Marceau with the Nile as regards protective features is so incontestably in favor of the latter, that they cannot be classed together for a moment. In speed, moreover, though this is not a point under consideration, the Nile has the advantage. It is impossible, however, to avoid the conviction that the Dupuy de Lome would be a most powerful and disagreeable enemy for either of the eight great ironclads of Great Britain now building to encounter on service. The Hood and Royal Sovereign have many vulnerable points. At any position outside of the dark and light colored portions of armor plate indicated in our drawing, they could be hulled with impunity with the lightest weapons. It is true that gun detachments and ammunition will be secure within the internal "crinolines," but how about the other men and materiel between decks? Now, the Dupuy de Lome may be riddled through and through bf a 131/2 in. shell if a Royal Sovereign ever succeeds in catching her; but from lighter weapons her between decks is almost secure. We cannot help feeling a sneaking admiration for the great French cruising battleship, with her 6,300 tons and 14,000 horse power, giving an easy speed of 20 knots in almost any weather, and protected by a complete 4 in. steel panoply, which will explode the shells of most of our secondary batteries on impact, or prevent their penetration. In fact, there is little doubt that the interior of the Trafalgar, whether as regards the secondary batteries or the unarmored ends, would be probably found to be a safer and pleasanter situation, in the event of action with a Dupuy de Lome, than either of the naked batteries or the upper works of the Royal Sovereign. This is what Sir E.J. Reed was so anxious to point out at the meeting of naval architects in 1889, when he described the modern British battleship as a "spoiled Trafalgar." There was perhaps some reason in what he said.—The Engineer.
* * * * *
DEMOLITION OF ROCKS UNDER WATER WITHOUT EXPLOSIVES-LOBNITZ SYSTEM.[1]
[Footnote 1: Read before the Engineer's Club, Philadelphia. Translated from Nouvelles Anodes de la Construction, March, 1890.]
By EDWIN S. CRAWLEY.
The methods of demolishing rocks by the use of explosives are always attended by a certain amount of danger, while at the same time there is always more or less uncertainty in regard to the final result of the operation. Especially is this the case when the work must be carried on without interrupting navigation and in the vicinity of constructions that may receive injury from the explosions.
Such were the conditions imposed in enlarging the Suez Canal in certain parts where the ordinary dredges could not be used.
Mr. Henry Lobnitz, engineer at Renfrew, has contrived a new method of procedure, designed for the purpose of enlarging and deepening the canal in those parts between the Bitter Lakes and Suez, where it runs over a rocky bed. It was necessary to execute the work without interrupting or obstructing traffic on the canal.
The principle of the system consists in producing a shattering of the rock by the action of a heavy mass let fall from a convenient height, and acting like a projectile of artillery upon the wall of a fortress.
From experiments made in the quarry of Craigmiller, near Edinburgh, with a weight of two tons shod with a steel point, it was found that with a fall of about 5.5 meters (18.04 ft.) there was broken up on an average more than 0.113 cubic meter (0.148 cubic yard) of hard rock per blow. The first blow, delivered 90 centimeters (2 ft. 111/2 in.) from the wall face, produced an almost imperceptible rent, a second or a third blow applied at the same place extended this opening often to a length of 1.50 meters (4 ft. 11 in.) and to a depth of from 90 to 120 centimeters (2 ft. 11 in. to 3 ft. 11 in.) The next blow opened the fissure and detached the block of rock.
The application of the same system under water upon an unknown surface would obviously modify the conditions of the experiment. Nevertheless, the results obtained with the "Derocheuse," the first dredging machine constructed upon this principle, have realized the hopes of the inventor.
This dredging machine was launched on the Clyde and reached Port Said in twenty days. It measures 55 meters (180 ft. 5 in.) in length, 12.20 meters (40 ft. 1 in.) in breadth, and 3.65 meters (12 ft.) in depth. Its mean draught of water is 2.75 meters (9 ft. 21/2 in.) It is divided into eighteen watertight compartments. Five steel-pointed battering rams, each of four tons weight, are arranged in line upon each side of the chain of buckets of the dredging machine. See Figs. 1 and 2. The battering rams, suspended by chains, are raised by hydraulic power to a height varying from 1.50 to 6 meters (4 ft. 11 in. to 19 ft. 8 in.), and are then let fall upon the rock. The mechanism of the battering rams is carried by a metallic cage which can be moved forward or backward by the aid of steam as the needs of the work require. A series of five battering rams gives from 200 to 300 blows per hour.
A dredging machine combined with the apparatus just described, raises the fragments of rock as they are detached from the bottom. A guide wheel is provided, which supports the chain carrying the buckets, and thus diminishes the stress upon the axles and bearings. With this guide wheel or auxiliary drum there is no difficulty in dredging to a depth of 12 meters (39 ft. 4 in.), while without this accessory it is difficult to attain a depth of 9 meters (29 ft. 6 in.)
A compound engine, with four cylinders of 200 indicated horse power, drives, by means of friction gear, the chain, which carries the buckets. If the buckets happen to strike against the rock, the friction gear yields until the excess of resistance has disappeared.
Fig. 3 indicates the manner in which the dredge is operated during the work. It turns alternately about two spuds which are thrust successively into the bottom and about which the dredge describes a series of arcs in a zigzag fashion. These spuds are worked by hydraulic power.
A three ton hand crane is placed upon the bridge for use in making repairs to the chain which carries the buckets. A six ton steam crane is placed upon the top of the cage which supports the hydraulic apparatus for raising the battering rams, thus permitting them to be easily lifted and replaced.
The dredging machine is also furnished with two screws driven by an engine of 300 indicated horse power, as well as with two independent boilers. Two independent series of pumps, with separate connections, feed the hydraulic lifting apparatus, thus permitting repairs to be made when necessary, without interrupting the work. A special machine with three cylinders drives the pumps of the condenser. An accumulator regulates the hydraulic pressure and serves to raise or lower the spuds.
At the end of the Suez Canal next to the Red Sea, the bottom consists of various conglomerates containing gypsum, sandstone and sometimes shells. It was upon a bed of this nature that the machine was first put to work. The mean depth of water, originally 8.25 meters (26 ft. 3 in.), was for a long time sufficient for the traffic of the canal; but as the variations in level of the Red Sea are from 1.8 to 3 meters (5 ft. 11 in. to 9 ft. 10 in.), the depth at the moment of low water is scarcely adequate for the constantly increasing draught of water of the steamers. Attempts were made to attack the rocky surface of the bottom with powerful dredges, but this method was expensive because it necessitated constant repairs to the dredges.
These last, although of good construction, seldom raised more than 153 cubic meters (200 cubic yards) in from eight to fifteen days. Their daily advance was often only from sixty to ninety centimeters (about 2 to 3 ft.), while with the "Derocheuse" it was possible to advance ten times as rapidly in dredging to the same depth. The bottom upon which the machine commenced its work was clean and of a true rocky nature. It was soon perceived that this conglomerate, rich in gypsum, possessed too great elasticity for the pointed battering rams to have their proper effect upon it. Each blow made a hole of from fifteen to sixty centimeters (6 in. to 2. ft.) in depth. A second blow, given even very near to the first, formed a similar hole, leaving the bed of the rock to all appearances intact between the two holes. This result, due entirely to the special nature of the rock, led to the fear that the action of the battering rams would be without effect. After some experimentation it was found that the best results were obtained by arranging the battering rams very near to the chain of buckets and by working the dredge and battering rams simultaneously. The advance at each oscillation was about 90 centimeters (about 3 ft.)
The results obtained were as follows: At first the quantity extracted varied much from day to day; but at the end of some weeks, on account of the greater experience of the crew, more regularity was obtained. The nature of the conglomerate was essentially variable, sometimes hard and tenacious, like malleable iron, then suddenly changing into friable masses surrounded by portions more elastic and richer in gypsum.
During the last five weeks at Port Tewfik, the expense, including the repairs, was 8,850 francs ($1,770.00) for 1,600 cubic meters (2,093 cubic yards) extracted. This would make the cost 5.52 francs per cubic meter, or $0.84 per cubic yard, not including the insurance, the interest and the depreciation of the plant.
After some improvements in details, suggested by practice, the machine was put in operation at Chalouf upon a hard rock, from 1.50 to 3 meters (4 ft. 11 in. to 9 ft. 10 in.) thick. The battering rams were given a fall of 1.80 meters (5 ft. 11 in.). To break the rock into fragments small enough not to be rejected by the buckets of the dredge, the operations of dredging and of disintegration were carried on separately, permitting the battering rams to work at a greater distance from the wall face. The time consumed in thus pulverizing the rock by repeated blows was naturally found to be increased. It was found more convenient to use only a single row of battering rams. The production was from about seven to eleven cubic meters (9.2 to 14.4 cubic yards) per hour. Toward the close of September, after it had been demonstrated that the "Derocheuse" was capable of accomplishing with celerity and economy the result for which it was designed, it was purchased by the Suez Canal Company.
During the month of September, an experiment, the details of which were carefully noted, extending over a period of sixteen days, gave the following results:
Crew (33 men), 140 hours. 2,012.50 francs $402.50 Coal, @ 87.50 francs ($7.50) per ton 787.50 francs 157.50 Oil and supplies 220.00 francs 44.00 Fresh water, 16 days 210.00 francs 42.00 Sundries 42.50 francs 8.50 ———————— ————- Total expense for removing 764 cubic meters (999.2 cubic yards), 3,272.50 francs $654.50
Average, 4.28 francs per cubic meter ($0.65 per cubic yard).
This result cannot be taken as a universal basis, because after a year's use there are numerous repairs to make to the plant, which would increase the average net cost. This, besides, does not include the cost of removal of the dredged material, nor the depreciation, the interest and the insurance.
It should be added on the other hand, however, that the warm season was far from being favorable to the energy and perseverance necessary to carry on successfully experiments of this kind. The temperature, even at midnight, was often 38 deg. C. (100.4 deg. F.). Still further, the work was constantly interrupted by the passage of ships through the canal. On an average not more than forty minutes' work to the hour was obtained. Notwithstanding this, there were extracted at Chalouf, on an average, 38.225 cubic meters (50 cubic yards) per day without interrupting navigation. At Port Tewfik, where there was much less inconvenience from the passage of ships, the work was carried on from eight to eleven hours per day and the quantity extracted in this time was generally more than 76 cubic meters (99.4 cubic yards).
In most cases the system could be simplified. The engine which works the dredge could, when not thus employed, be used to drive the pumps. The propelling engine could also be used for the same purpose.
The results obtained at Suez indicate the appreciable advantages arising from the application of this system to the works of ports, rivers and canals, and ever, to the work of cutting in the construction of roads and railroads.
* * * * *
PROGRESS IN ENGINEERING.
Mr. T. Forster Brown, in his address to the Mechanical Science Section of the British Association, said that great progress had been made in mechanical science since the British Association met in the principality of Wales eleven years ago; and some of the results of that progress were exemplified in our locomotives, and marine engineering, and in such works as the Severn Tunnel, the Forth and Tay Bridges, and the Manchester Ship Canal, which was now in progress of construction. In mining, the progress had been slow, and it was a remarkable fact that, with the exception of pumping, the machinery in use in connection with mining operations in Great Britain had not, in regard to economy, advanced so rapidly as had been the case in our manufactures and marine. This was probably due, in metalliferous mining, to the uncertain nature of the mineral deposits not affording any adequate security to adventurers that the increased cost of adopting improved appliances would be reimbursed; while in coal mining, the cheapness of fuel, the large proportion which manual labor bore to the total cost of producing coal, and the necessity for producing large outputs with the simplest appliances, explained the reluctance with which high pressure steam compound engines, and other modes embracing the most modern and approved types of economizing power had been adopted. Metalliferous mining, with the exception of the working of iron ore, was not in a prosperous condition; but in special localities, where the deposits of minerals were rich and profitable, progress had been made within a recent period by the adoption of more economical and efficient machinery, of which the speaker quoted a number of examples. Reference was also made to the rapid strides made in the use of electricity as a motive power, and to the mechanical ventilation of mines by exhaustion of the air.
COAL MINES.
Summarizing the position of mechanical science, as applied to the coal mining industry in this country, Mr. Brown observed that there was a general awakening to the necessity of adopting, in the newer and deeper mines, more economical appliances. It was true it would be impracticable, and probably unwise, to alter much of the existing machinery, but, by the adoption of the best known types of electrical plant, and air compression in our new and deep mines, the consumption of coal per horse power would be reduced, and the extra expense, due to natural causes, of producing minerals from greater depths would be substantially lessened. The consumption of coal at the collieries of Great Britain alone probably exceeded 10,000,000 tons per annum, and the consumption per horse power was probably not less than 6 lb. of coal, and it was not unreasonable to assume that, by the adoption of more efficient machinery than was at present in general use, at least one-half of the coal consumed could be saved. There was, therefore, in the mines of Great Britain alone a wide and lucrative field for the inventive ingenuity of mechanical engineers in economizing fuel, and especially in the successful application of new methods for dealing with underground haulage, in the inner workings of our collieries, more especially in South Wales, where the number of horses still employed was very large.
STEAM TRAMS AND ELECTRIC TRAMS.
Considerable progress had within recent years been made in the mechanical appliances intended to replace horses on our public tram lines. The steam engine now in use in some of our towns had its drawbacks as as well as its good qualities, as also had the endless rope haulage, and in the case of the latter system, anxiety must be felt when the ropes showed signs of wear. The electrically driven trams appeared to work well. He had not, however, seen any published data bearing on the relative cost per mile of these several systems, and this information, when obtained, would be of interest. At the present time, he understood, exhaustive trials were being made with an ammonia gas engine, which, it was anticipated, would prove both more economical and efficient than horses for tram roads. The gas was said to be produced from the pure ammonia, obtained by distillation from commercial ammonia, and was given off at a pressure varying from 100 to 150 lb. per square inch. This ammonia was used in specially constructed engines, and was then exhausted into a tank containing water, which brought it back into its original form of commercial ammonia, ready for redistillation, and, it was stated, with a comparatively small loss.
* * * * *
IMPROVED CHANGEABLE SPEED GEARING.
This is the invention of Lawrence Heath, of Macedon, N.Y., and relates to that class of changeable speed gearing in which a center pinion driven at a constant rate of speed drives directly and at different rates of speed a series of pinions mounted in a surrounding revoluble case or shell, so that by turning the shell one or another of the secondary pinions may be brought into operative relation to the parts to be driven therefrom.
The aim of my invention is to so modify this system of gearing that the secondary pinions may receive a very slow motion in relation to that of the primary driving shaft, whereby the gearing is the better adapted for the driving of the fertilizer-distributers of grain drills from the main axle, and for other special uses.
Fig. 1 is a side elevation. Fig. 2 is a vertical cross section.
A represents the main driving shaft or axle, driven constantly and at a uniform speed, and B is the pinion-supporting case or shell, mounted loosely on and revoluble around the axle, but held normally at rest by means of a locking bolt, C, or other suitable locking device adapted to enter notches, c, in the shell.
D is the primary driving pinion, fixed firmly to the axle and constantly engaging the pinion, E, mounted on a stud in the shell. The pinion, E, is formed integral with or firmly secured to the smaller secondary pinion, F, which in turn constantly engages and drives the center pinion, G, mounted to turn loosely on the axle within the shell, so that it is turned in the same direction as the axle, but at a slower speed.
F', F_{2}, F_{3}, F_{4}, etc., represent additional secondary pinions grouped around the center pinion, mounted on studs in the shell, and made of different diameters, so that they are driven by the center pinion at different speeds. Each of the secondary pinions is formed with a neck or journal, _f_, projected out through the side of the shell, so that the external pinion, H, may be applied to any one of the necks at will in order to communicate motion thence to the gear, I, which occupies a fixed position, and from which the fertilizer or other mechanism is driven.
In order to drive the gear, I, at one speed or another, as may be demanded, it is only necessary to apply the pinion, H, to the neck of that secondary pinion which is turning at the appropriate speed and then turn the shell bodily around the axle until the external pinion is carried into engagement with gear I, when the shell is again locked fast. The axle communicates motion through D, E, and P to the center pinion, which in turn drives all the secondary pinions except F. If the external pinion is applied to F, it will receive motion directly therefrom; but if applied to either of the secondary pinions, it will receive motion through or by way of the center pinion. It will be seen that all the pinions are sustained and protected within the shell.
The essence of the invention lies in the introduction of the pinions D and E between the axle and the series of secondary pinions to reduce the speed.
* * * * *
ELECTRICAL STANDARDS.
Nature states that the Queen's Printers are now issuing the Report (dated July 23, 1891) to the President of the Board of Trade, of the Committee appointed to consider the question of constructing standards for the measurement of electricity. The committee included Mr. Courtenay Boyle, C.B., Major P. Cardew, R.E., Mr. E. Graves, Mr. W.H. Preece, F.R.S., Sir W. Thomson, F.R.S., Lord Rayleigh, F.R.S., Prof. G. Carey Foster, F.R.S., Mr. R.T. Glazebrook, F.R. S., Dr. John Hopkinson, F.R.S., Prof. W.E. Ayrton, F.R.S.
In response to an invitation, the following gentlemen attended and gave evidence: On behalf of the Association of Chambers of Commerce, Mr. Thomas Parker and Mr. Hugh Erat Harrison; on behalf of the London Council, Prof. Silvanus Thompson; on behalf of the London Chamber of Commerce, Mr. R. E. Crompton. The Committee were indebted to Dr. J.A. Fleming and Dr. A. Muirhead for valuable information and assistance; and they state that they had the advantage of the experience and advice of Mr. H. J. Chaney, the Superintendent of Weights and Measures. The Secretary to the Committee was Sir T.W. P. Blomefield, Bart.
The following are the resolutions of the Committee:
Resolutions.
(1) That it is desirable that new denominations of standards for the measurement of electricity should be made and approved by Her Majesty in Council as Board of Trade standards.
(2) That the magnitudes of these standards should be determined on the electro-magnetic system of measurement with reference to the centimeter as unit of length, the gramme as unit of mass, and the second as unit of time, and that by the terms centimeter and gramme are meant the standards of those denominations deposited with the Board of Trade.
(3) That the standard of electrical resistance should be denominated the ohm, and should have the value 1,000,000,000 in terms of the centimeter and second.
(4) That the resistance offered to an unvarying electric current by a column of mercury of a constant cross sectional area of 1 square millimeter, and of a length of 106.3 centimeters at the temperature of melting ice may be adopted as 1 ohm.
(5) That the value of the standard of resistance constructed by a committee of the British Association for the Advancement of Science in the years 1863 and 1864, and known as the British Association unit, may be taken as 0.9866 of the ohm.
(6) That a material standard, constructed in solid metal, and verified by comparison with the British Association unit, should be adopted as the standard ohm.
(7) That for the purpose of replacing the standard, if lost, destroyed, or damaged, and for ordinary use, a limited number of copies should be constructed, which should be periodically compared with the standard ohm and with the British Association unit.
(8) That resistances constructed in solid metal should be adopted as Board of Trade standards for multiples and sub-multiples of the ohm.
(9) That the standard of electrical current should be denominated the ampere, and should have the value one-tenth (0.1) in terms of the centimeter, gramme, and second.
(10) That an unvarying current which, when passed through a solution of nitrate of silver in water, in accordance with the specification attached to this report, deposits silver at the rate of 0.001118 of a gramme per second, may be taken as a current of 1 ampere.
(11) That an alternating current of 1 ampere shall mean a current such that the square root of the time-average of the square of its strength at each instant in amperes is unity.
(12) That instruments constructed on the principle of the balance, in which, by the proper disposition of the conductors, forces of attraction and repulsion are produced, which depend upon the amount of current passing, and are balanced by known weights, should be adopted as the Board of Trade standards for the measurement of current, whether unvarying or alternating.
(13) That the standard of electrical pressure should be denominated the volt, being the pressure which, if steadily applied to a conductor whose resistance is 1 ohm, will produce a current of 1 ampere.
(14) That the electrical pressure at a temperature of 62 deg. F. between the poles or electrodes of the voltaic cell known as Clark's cell may be taken as not differing from a pressure of 1.433 volts by more than an amount which will be determined by a sub-committee appointed to investigate the question, who will prepare a specification for the construction and use of the cell.
(15) That an alternating pressure of 1 volt shall mean a pressure such that the square root of the time average of the square of its value at each instant in volts is unity.
(16) That instruments constructed on the principle of Sir W. Thomson's quadrant electrometer used idiostatically, and for high pressure instruments on the principle of the balance, electrostatic forces being balanced against a known weight, should be adopted as Board of Trade standards for the measurement of pressure, whether unvarying or alternating.
We have adopted the system of electrical units originally defined by the British Association for the Advancement of Science, and we have found in its recent researches, as well as in the deliberations of the International Congress on Electrical Units, held in Paris, valuable guidance for determining the exact magnitudes of the several units of electrical measurement, as well as for the verification of the material standards.
We have stated the relation between the proposed standard ohm and the unit of resistance originally determined by the British Association, and have also stated its relation to the mercurial standard adopted by the International Conference.
We find that considerations of practical importance make it undesirable to adopt a mercurial standard; we have, therefore, preferred to adopt a material standard constructed in solid metal.
It appears to us to be necessary that in transactions between buyer and seller, a legal character should henceforth be assigned to the units of electrical measurement now suggested; and with this view, that the issue of an Order in Council should be recommended, under the Weights and Measures Act, in the form annexed to this report.
Specification referred to in Resolution 10.
In the following specification the term silver voltameter means the arrangement of apparatus by means of which an electric current is passed through a solution of nitrate of silver in water. The silver voltameter measures the total electrical quantity which has passed during the time of the experiment, and by noting this time the time average of the current, or if the current has been kept constant, the current itself, can be deduced.
In employing the silver voltameter to measure currents of about 1 ampere, the following arrangements should be adopted. The kathode on which the silver is to be deposited should take the form of a platinum bowl not less than 10 cm. in diameter, and from 4 to 5 cm. in depth.
The anode should be a plate of pure silver some 30 square cm. in area and 2 or 3 millimeters in thickness.
This is supported horizontally in the liquid near the top of the solution by a platinum wire passed through holes in the plate at opposite corners. To prevent the disintegrated silver which is formed on the anode from falling on to the kathode, the anode should be wrapped round with pure filter paper, secured at the back with sealing wax.
The liquid should consist of a neutral solution of pure silver nitrate, containing about 15 parts by weight of the nitrate to 85 parts of water.
The resistance of the voltameter changes somewhat as the current passes. To prevent these changes having too great an effect on the current, some resistance besides that of the voltameter should be inserted in the circuit. The total metallic resistance of the circuit should not be less than 10 ohms.
Method of making a Measurement.—The platinum bowl is washed with nitric acid and distilled water, dried by heat, and then left to cool in a desiccator. When thoroughly dry, it is weighed carefully.
It is nearly filled with the solution, and connected to the rest of the circuit by being placed on a clean copper support, to which a binding screw is attached. This copper support must be insulated.
The anode is then immersed in the solution, so as to be well covered by it, and supported in that position; the connections to the rest of the circuit are made.
Contact is made at the key, noting the time of contact. The current is allowed to pass for not less than half an hour, and the time at which contact is broken is observed. Care must be taken that the clock used is keeping correct time during this interval.
The solution is now removed from the bowl, and the deposit is washed with distilled water and left to soak for at least six hours. It is then rinsed successively with distilled water and absolute alcohol, and dried in a hot-air bath at a temperature of about 160 deg. C. After cooling in a desiccator, it is weighed again. The gain in weight gives the silver deposited.
To find the current in amperes, this weight, expressed in grammes, must be divided by the number of seconds during which the current has been passed, and by 0.001118.
The result will be the time average of the current, if during the interval the current has varied.
In determining by this method the constant of an instrument the current should be kept as nearly constant as possible, and the readings of the instrument taken at frequent observed intervals of time. These observations give a curve from which the reading corresponding to the mean current (time average of the current) can be found. The current, as calculated by the voltameter, corresponds to this reading.
* * * * *
THE TWO OR THREE PHASE ALTERNATING CURRENT SYSTEMS.
By CARL HERING.
The occasion of the transmission of power from Lauffen to Frankfort has brought to the notice of the profession more than ever before the two or three phase alternating current system, described as early as 1887-88 by various electricians, among whom are Tesla, Bradley, Haselwander and others. As to who first invented it, we have nothing to say here, but though known for some years it has not until quite recently been of any great importance in practice.
Within the last few years, however, Mr. M. Von Dolivo-Dobrowolsky, electrical engineer of the Allgemeine Elektricitats Gesellschaft, of Berlin, has occupied himself with these currents. His success with motors run with such currents was the origin of the present great transmission of power exhibit at Frankfort, the greatest transmission ever attempted. His investigation in this new sphere, and his ability to master the subject from a theoretical or mathematical standpoint, has led him to find the objections, the theoretically best conditions, etc. This, together with his ingenuity, has led him to devise an entirely new and very ingenious modification, which will no doubt have a very great effect on the development of alternating current motors.
It is doubtless well known that if, as in Fig. 1, a Gramme ring armature is connected to leads at four points as shown and a magnet is revolved inside of it (or if the ring is revolved in a magnetic field and the current led off by contact rings instead of a commutator), there will be two alternating currents generated, which will differ from each other in their phases only. When one is at a maximum the other is zero. When such a double current is sent into a similarly constructed motor it will produce or generate what might be called a rotary field, which is shown diagrammatically in the six successive positions in Fig. 2. The winding here is slightly different, but it amounts to the same thing as far as we are concerned at present. This is what Mr. Dobrowolsky calls an "elementary" or "simply" rotary current, as used in the Tesla motors. A similar system, but having three different currents instead of two, is the one used in the Lauffen transmission experiment referred to above.
In investigating this subject Mr. Dobrowolsky found that the best theoretical indications for such a system would be a large number of circuits instead of only two or three, each differing from the next one by only a small portion of a wave length; the larger their number the better theoretically. The reason is that with a few currents the resulting magnetism generated in the motor by these currents will pulsate considerably, as shown in Fig. 3, in which the two full lines show the currents differing by 90 degrees. The dotted line above these shows how much the resulting magnetism will pulsate. With two such currents this variation in magnetism will be about 40 degrees above its lowest value. Now, such a variation in the field is undesirable, as it produces objectionable induction effects, and it has the evil effect of interfering with the starting of the motor loaded, besides affecting the torque considerably if the speed should fall slightly below that for synchronism. A perfect motor should not have these faults, and it is designed to obviate them by striving to obtain a revolving field in which the magnetism is as nearly constant as possible.
If there are two currents differing by 90 degrees, this variation of the magnetism will be about 40 per cent.; with three currents differing 60 degrees, about 14 per cent; with six currents differing 30 degrees it will be only about 4 per cent., and so on. It will be seen, therefore, that by doubling the three-phase system the pulsations are already very greatly reduced. But this would require six wires, while the three-phase system requires only three wires (as each of the three leads can readily be shown to serve as a return lead for the other two in parallel). It is to combine the advantages of both that he designed the following very ingenious system. By this system he can obtain as small a difference of phase as desired, without increasing the number of wires above three, a statement which might at first seem paradoxical.
Before explaining this ingenious system, it might be well to call attention to a parallel case to the above in continuous current machines and motors. The first dynamos were constructed with two commutator bars. They were soon found to work much better with four, and finally still better as the number of commutator bars (or coils) was increased, up to a practical limit. Just as the pulsations in the continuous current dynamos were detrimental to proper working, so are these pulsations in few-phased alternating current motors, though the objections manifest themselves in different ways—in the continuous current motors as sparking and in the alternating current motors as detrimental inductive effects.
The underlying principle of this new system may be seen best in Figs. 4, 5, 6, 7 and 8. In Fig. 4 are shown two currents, I{1} and I{2}, which differ from each other by an angle, D. Suppose these two currents to be any neighboring currents in a simple rotary current system. Now, if these two currents be united into one, as shown in the lower part of the figure, the resulting current, I, will be about as shown by the dotted line; that is, it will lie between the other two and at its maximum point, and for a difference of phases equal to 90 degrees it will be about 1.4 times as great as the maximum of either of the others; the important feature is that the phase of this current is midway between that of the other two. Fig. 5 shows the winding of a cylinder armature and Fig. 7 that, of a Gramme armature for a simple three-phase current with three leads, with which system we assume that the reader is familiar.
The two figures, 4 and 5 (or 7), correspond with each other in so far as the currents in the three leads, shown in heavy lines, have a phase between those of the two which compose them. Referring now to Fig. 6 (or 8), which is precisely like Fig. 5 (or 7), except that it has an additional winding shown in heavy lines, it will be seen that each of the three leads, shown in heavy lines, is wound around the armature before leaving it, forming an additional coil lying between the two coils with which it is in series. The phase of the heavy line currents was shown in Fig. 4 to lie between the other two. Therefore, in the armature in Fig. 6 (or 8) there will be six phases, while in Fig. 5 there are only three, the number of leads (three) remaining the same as before. This is the fundamental principle of this ingenious invention. To have six phases in Fig. 5 would require six leads, but in Fig. 6 precisely the same result is obtained with only three leads. In the same way the three leads in Fig. 6 might again be combined and passed around the armature again, and so on forming still more phases, without increasing the number of leads. Figs. 7 and 8 compound with 5 and 6 and show the same system for a Gramme ring instead of a cylinder armature.
As was stated in the early part of this description, the main object in a rotary current motor is to have a magnetic field which is as nearly constant in intensity as possible, and which changes only its position, that is, its axis. But in Fig. 4 it was shown that the current I (in dotted lines) is greater than the others (about as 1.4 to 1 for a phase difference of 90 degrees). If therefore the coils in Fig. 6 or 8 were all alike, the magnetism generated by the heavy line coils would be greater than that generated by the others, and would therefore produce very undesirable pulsations in the magnetic fields; but as the magnetism depends on the ampere turns, it is necessary merely to have correspondingly fewer turns on these coils, as compared with the others. This is shown diagrammatically in Figs. 6 and 8, in which the heavy line coils have less windings than the others. In practice it is not always possible to obtain the exact ratio of 1 to 1.4, for instance, but even if this ratio is obtained only approximately, it nevertheless reduces the pulsations very materially below what they would be with half the number of phases. It is therefore not necessary in practice to have more than an approximation to the exact conditions.
Fig. 9 shows a multiple phase armature having double the number of phases as Fig. 1, and would according to the old system, therefore, require eight leads. Fig. 10 shows the new system with the same number of phases as in Fig. 9, but requiring only four leads instead of eight. Figs. 11 and 12 correspond with Figs. 7 and 8 and show the windings for a multipolar motor in the two systems.
These figures show how a motor may be wound so as to be a multiple phase motor, although the current entering the motor is a simple, elementary three or two phase current, which can be transformed by means of a simple three or two phase current transformer, before entering the motor, such transformers as are used at present in the Lauffen-Frankfort transmission. But the same principle as that for the motor may also be applied to transformers themselves, as shown in Figs. 13 and 14. Fig. 13 shows a set of transformers which are fed by a simple three-phase current shown in heavy lines, and which gives in its secondary circuit a multiple phase rotary current. The connections for the primary circuit of a transformer with six coils are shown diagrammatically in Fig. 15, the numbers 1 to 6 representing the succession of the phases. Fig. 14 shows a transformer for a two-phase current with four leads, transforming into a multiple phase current of 16 leads. The transformer in this figure is a single "interlocked" transformer in which the fields are magnetically connected and not independent of each other as in Fig. 13. This has advantages in the regulation of currents, which do not exist in Fig. 13, but which need not be entered into here. The transformers used in the Lauffen-Frankfort transmission are similar, magnetically, to Fig. 14, only that they are for a simple three-phase current in both primary and secondary circuits. Attention is also called to the difference in the connections of secondary circuits in Figs. 13 and 14; in the former they are connected in a closed circuit similarly to an ordinary closed circuit armature, while in Fig. 14 they are independent as far as the currents themselves are concerned, though magnetically their cores are connected. It is not the intention to enter into a discussion of the relative values of these various connections, but merely to draw attention to the wide range of the number of combinations which this system admits of.—Electrical World.
* * * * *
THE LONDON PARIS TELEPHONE.[1]
[Footnote 1: Paper read before the British Association.—Elec. Engineer.]
By W.H. Preece, F.R.S.
1. I have already on two occasions, at Newcastle and at Leeds, brought this subject before Section G, and have given the details of the length and construction of the proposed circuit.
I have now to report not only that the line has been constructed and opened to the public, but that its success, telephonic and commercial, has exceeded the most sanguine anticipations. Speech has been maintained with perfect clearness and accuracy. The line has proved to be much better than it ought to have been, and the purpose of this paper is to show the reason why.
The lengths of the different sections of the circuit are as follows:
London to St. Margaret's Bay 84.5 miles. St. Margaret's Bay to Sangatte (cable). 23.0 " Sangatte to Paris. 199.0 " Paris underground. 4.8 " ——- Total. 311.3 "
The resistances are as follows:
Paris underground. 70 ohms. French line. 294 " Cable. 143 " English line. 183 " —- Total (R) 693 "
The capacities are as follows:
Paris underground. 0.43 microfarads. French line. 3.33 " Cable. 5.52 " English line. 1.32 " —— Total (K). 10.62 "
693 x 10.62 = 7,359 = K R
a product which indicates that speech should be very good.
2. Trials of Apparatus.—The preliminary trials were made during the month of March between the chief telegraph offices of the two capitals, and the following microphone transmitters were compared:
Ader. Pencil form. Berliner. Granular form. D'Arsonval. Pencil " DeJongh. " " Gower Bell. " " Post office switch instrument. Granules and lamp filaments. Roulez. Lamp filaments. Turnbull. Pencil form. Western Electric. Granular.
The receivers consisted of the latest form of double-pole Bell telephones with some Ader and D'Arsonval receivers for comparison. After repeated trials it was finally decided that the Ader, D'Arsonval, Gower-Bell (with double-pole receivers instead of tubes), Roulez, and Western Electric were the best, and were approximately equal.
These instruments were, therefore, selected for the further experiments, which consisted of using local extensions in Paris and London. The wires were in the first instance extended at the Paris end to the Observatory through an exchange at the Avenue des Gobelines. The length of this local line is 7 kms. The wires are guttapercha-covered, placed underground, and not suitable for giving the best results.
The results were, however, fairly satisfactory. The wires were extended to the Treasury in London by means of the ordinary underground system. The distance is about two miles, and although the volume of sound and clearness of articulation were perceptibly reduced by these additions to the circuit, conversation was quite practicable.
Further trials were also made from the Avenue des Gobelines on underground wires of five kilometers long, and also with some renters in Paris with fairly satisfactory results. The selected telephones were equally efficient in all cases, which proves that to maintain easy conversation when the trunk wires are extended to local points it is only necessary that the local lines shall be of a standard not lower than that of the trunk line. The experiments also confirm the conclusion that long-distance speaking is solely a question of the circuit and its environments, and not one of apparatus. The instruments finally selected for actual work were Gower-Bell for London and Roulez for Paris.
3. The results are certainly most satisfactory. There is no circuit in or out of London on which speech is more perfect than it is between London and Paris. In fact, it is better than I anticipated, and better than calculation led me to expect. Speech has been possible not only to Paris but through Paris to Bruxelles, and even, with difficulty, through Paris to Marseilles, a distance of over 900 miles. The wires between Paris and Marseilles are massive copper wires specially erected for telephone business between those important places.
4. Business Done.—The charge for a conversation between London and Paris is 8 s. for three minutes' complete use of the wire. The demand for the wire is very considerable. The average number of talks per day, exclusive of Sunday, is 86. The maximum has been 108. We have had as many as 19 per hour—the average is 15 during the busy hours of the day. As an instance of what can be done, 150 words per minute have been dictated in Paris and transcribed in London by shorthand writing. Thus in three minutes 450 words were recorded, which at 8 s. cost five words for a penny.
5. Difficulties.—The difficulties met with in long-distance speaking are several, and they may be divided into (a) those due to external disturbances and (b) those due to internal opposition.
(a.) Every current rising and falling in the neighborhood of a telephone line within a region, say, of 100 yards, whether the wire conveying it be underground or overground, induces in the telephone circuit another current, producing in the telephone a sound which disturbs speech, and if the neighboring wires are numerous and busy, as they are on our roads and railways, these sounds became confusing, noisy, and ultimately entirely preventive of speech. This disturbance is, however, completely removed by forming the telephone circuit of two wires placed as near to each other as possible, and twisted around each other without touching, so as to maintain the mean average distance of each wire from surrounding conductors the same everywhere. Thus similar currents are induced in each of the two wires, but being opposite in direction, as far as the circuit is concerned, they neutralize each other, and the circuit, therefore, becomes quite silent.
In England we make the two wires revolve completely round each other in every four poles, but in France it is done in every six poles. The reason for the change is the fact that in the English plan the actual crossing of the wires takes place in the span between the poles, while in the French plan it takes place at the poles. This is supposed to reduce the liability of the wires to be thrown into contact with each other by the wind, but, on the other hand, it diminishes the geometrical symmetry of the wires—so very essential to insure silence. As a matter of fact, contacts do not occur on well constructed lines, and I think our English wires, being more symmetrical, are freer from external disturbance than those in France.
(b.) The internal opposition arises from the resistance, R, the capacity, K, and the electromagnetic inertia, L, of the circuit. A current of electricity takes time to rise to its maximum strength and time to fall back again to zero. Every circuit has what is called its time constant, t, Fig. 1, which regulates the number of current waves which can be transmitted through it per second. This is the time the current takes to rise from zero to its working maximum, and the time it takes to fall from this maximum to zero again, shown by the shaded portions of the figure; the duration of the working current being immaterial, and shown by the unshaded portion.
The most rapid form of quick telegraphy requires about 150 currents per second, currents each of which must rise and fall in 1/150 of a second, but for ordinary telephone speaking we must have about 1,500 currents per second, or the time which each current rises from zero to its maximum intensity must not exceed 1/3000 part of a second. The time constant of a telephone circuit should therefore not be less than 0.0003 second.
Resistance alone does not affect the time constant. It diminishes the intensity or strength of the currents only; but resistance, combined with electromagnetic inertia and with capacity, has a serious retarding effect on the rate of rise and fall of the currents. They increase the time constant and introduce a slowness which may be called retardance, for they diminish the rate at which currents can be transmitted. Now the retardance due to electromagnetic inertia increases directly with the amount of electromagnetic inertia present, but it diminishes with the amount of resistance of the conductor. It is expressed by the ratio L/R while that due to capacity increases directly, both with the capacity and with the resistance, and it is expressed by the product, K R. The whole retardance, and, therefore, the speed of working the circuit or the clearness of speech, is given, by the equation
L —- + K R = t R
or L + K R squared = R t
Now in telegraphy we are not able altogether to eliminate L, but we can counteract it, and if we can make Rt = 0, then
L = - K R squared
which is the principle of the shunted condenser that has been introduced with such signal success in our post office service, and has virtually doubled the carrying capacity of our wires.
K R = t
This is done in telephony, and hence we obtain the law of retardance, or the law by which we can calculate the distance to which speech is possible. All my calculations for the London and Paris line were based on this law, which experience has shown it to be true.
How is electromagnetic inertia practically eliminated? First, by the use of two massive copper wires, and secondly by symmetrically revolving them around each other. Now L depends on the geometry of the circuit, that is, on the relative form and position of the different parts of the circuit, which is invariable for the same circuit, and is represented by a coefficient, [lambda]. It depends also on the magnetic qualities of the conductors employed and of the space embraced by the circuit. This specific magnetic capacity is a variable quantity, and is indicated by [mu] for the conductor and by [mu]_{0} for air. It depends also on the rate at which currents rise and fall, and this is indicated by the differential coefficient dC / dt. It depends finally on the number of lines of force due to its own current which cut the conductor in the proper direction; this is indicated by [beta]. Combining these together we can represent the electromagnetic inertia of a metallic telephone circuit as
L = [lambda] ([mu] + [mu]_{0}) dC/dt x [beta]
Now, [lambda] = 2 log (d squared/a squared) Hence the smaller we make the distance, d, between the wires, and the greater we make their diameter, a, the smaller becomes [lambda]. It is customary to call the value of [mu] for air, and copper, 1, but this is purely artificial and certainly not true. It must be very much less than one in every medium, excepting the magnetic metals, so much so that in copper it may be neglected altogether, while in the air it does not matter what it is, for by the method of twisting one conductor round the other, the magnetization of the air space by the one current of the circuit rotating in one direction is exactly neutralized by that of the other element of the circuit rotating in the opposite direction.
Now, [beta], in two parallel conductors conveying currents of the same sense, that is flowing in the same direction, is retarding, Fig. 2, and is therefore a positive quantity, but when the currents flow in opposite directions, as in a metallic loop, Fig. 3, they tend to assist each other and are of a negative character. Hence in a metallic telephone circuit we may neglect L in toto as I have done.
I have never yet succeeded in tracing any evidence of electromagnetic inertia in long single copper wires, while in iron wires the value of L may certainly be taken at 0.005 henry per mile.
In short metallic circuits, say of lengths up to 100 miles, this negative quantity does not appear, but in the Paris-London circuit this helpful mutual action of opposite currents comes on in a peculiar way. The presence of the cable introduces a large capacity practically in the center of the circuit. The result is that we have in each branch of the circuit between the transmitter, say, at London and the cable at Dover, extra currents at the commencement of the operation, which, flowing in opposite directions, mutually react on each other, and practically prepare the way for the working currents. The presence of these currents proved by the fact that when the cable is disconnected at Calais, as shown in Fig. 5, and telephones are inserted in series, as shown at D and D', speech is as perfect between London and St. Margaret's Bay as if the wires were connected across, or as if the circuit were through to Paris. Their effect is precisely the same as though the capacity of the aerial section were reduced by a quantity, M, which is of the same dimension or character as K. Hence, our retardance equation becomes
R (K - M) = t
Thus it happens that the London-Paris telephone works better than was expected. The nature of M is probably equivalent to about 0.0075 [phi] per mile, and therefore K should be also about 0.0075 [phi] instead of 0.0156 [phi] per mile. This helpful action of mutual induction is present in all long circuits, and it is the reason why we were able to speak to Brussels and even to Marseilles. It also appears in every metallic loop, and vitiates the measurements of electromagnetic inertia and of capacity of loops. Thus, if we measure the capacity of a loop as compared with a single wire, the amount per mile may be 50 per cent. greater than it ought to be; while if we measure the capacity of one branch of a circuit under the conditions of the London-Paris telephone line, it may be 50 per cent. less than it ought to be. This effect of M is shown by the dotted line in Fig. 1.
Telephonic currents—that is, currents induced in the secondary wire of an induction coil due to the variation of microphonic currents in the primary wire—are not alternating currents. They do not follow the constant periodic law, and they are not true harmonic sine functions of the time. The microphonic currents are intermittent or pulsatory, and always flow in the same direction. The secondary currents are also always of the same sign, as are the currents in a Ruhmkorff coil, and as are the currents in high vacua with which Crookes has made us so familiar. Moreover, the frequency of these currents is a very variable quantity, not only due to the various tones of voices, but to the various styles of articulation. Hence the laws of periodic alternate currents following the sine function of the time fail when we come to consider microphones and telephones. It is important to bear this in mind, for nearly everything that has hitherto been written on the subject assumes that telegraphic currents follow the periodic sine law. The currents derived from Bell's original magneto-transmitters are alternate, and comply more nearly with the law. The difference between them and microphones is at once perceptible. Muffling and disturbance due to the presence of electromagnetic inertia become evident, which are absent with microphones. I tested this between London and St. Margaret's, and found the effect most marked.
7. Lightning.—A metallic telephone circuit may have a static charge induced upon it by a thunder cloud, as shown in Fig. 6. Such a charge is an electric strain which is released when the charged cloud flashes into the earth or into a neighboring cloud. If there be electromagnetic inertia present, the charge will surge backward and forward through the circuit until it dies out. If there be no E.M.F. present it will cease suddenly, and neutrality will be attained at once. Telephone circuits indicate the operation by peculiar and characteristic sounds. An iron wire circuit produces a long swish or sigh, but a copper wire circuit like the Paris-London telephone emits a short, sharp report, like the crack of a pistol, which is sometimes startling, and has created fear, but there is no danger or liability to shock. Indeed, the start has more than once thrown the listener off his stool, and has led to the belief that he was knocked down by lightning.
8. The future of telephone working, especially in large cities, is one of underground wires, and the way to get over the difficulties of this kind of work is perfectly clear. We must have metallic circuits, twisted wires, low resistance, and low capacity. In Paris a remarkable cable, made by Fortin-Herman, gives an exceedingly low capacity—viz., only 0.069 [phi] per mile. In the United States they are using a wire insulated with paper which gives 0.08 [phi] per mile. We are using in London Fowler-Waring cable giving a capacity of 1.8 [phi] per mile, the capacity of gutta-covered wire being 3 [phi] per mile.
* * * * *
THE MANUFACTURE OF PHOSPHORUS BY ELECTRICITY.
One of the most interesting of the modern applications of electricity to the manufacture of chemicals is to be found in the recently perfected process known as the Readman-Parker process, after the inventors Dr. J.B. Readman, F.R.S.E., etc., of Edinburgh, and Mr. Thomas Parker; the well known practical electrician, of Wolverhampton.
Before giving an account of this process, which has advanced beyond the experimental to the industrial stage, it may be well to recall the fact that for several years past Dr. Readman has been devoting an enormous expenditure of labor, time and money to the perfection of a process which shall cheapen the production of phosphorus by dispensing altogether with the use of sulphuric acid for decomposing the phosphate of lime which forms the raw material of the phosphorus manufacturer, and also with the employment of fire clay retorts for distilling the desiccated mixture of phosphoric acid and carbon which usually forms the second stage of the operation.
The success of the recent applications of electricity in the production of certain metals and alloys led Dr. Readman to try this source of energy in the manufacture of phosphorus, and the results of the first series of experiments were so encouraging that he took out provisional protection on October 18, 1888, for preparing this valuable substance by its means.
The experiments were carried on at this time on a very small scale, the power at disposal being very limited in amount. Yet the elements of success appeared to be so great, and the decomposition of the raw material was so complete, that the process was very soon prosecuted on the large scale.
After a good deal of negotiation with several firms that were in a position to supply the electric energy required, Dr. Readman finally made arrangements with the directors of the Cowles Company, limited, of Milton, near Stoke-on-Trent, the well known manufacturers of alloys of aluminum, for a lease of a portion of their works and for the use of the entire electrical energy they produced for certain portions of the day.
The experiments on the large scale had not advanced very far before Dr. Readman became aware that another application for letters patent for producing phosphorus had been made by Mr. Thomas Parker, of Wolverhampton, and his chemist, Mr. A.E. Robinson. Their joint patent is dated December 5, 1888, and was thus applied for only seven weeks after Dr. Readman's application had been lodged.
It appeared that Mr. Parker had conducted a number of experiments simultaneously but quite independently of those carried on by Dr. Readman, and that he was quite unaware—as the latter was unaware—of any other worker in this field. It was no small surprise, therefore, to find during an interview which took place between these rival inventors some time after the date referred to, that the two patents were on practically the same lines, namely, the production of phosphorus by electricity.
Their interests lay so much together that, after some delay, they arranged to jointly work out the process, and the result has been the formation of a preliminary company and the erection on a large scale of experimental plant in the neighborhood of Wolverhampton to prove the commercial success of the new system of manufacturing phosphorus.
Before describing these experimental works it may be as well to see with what plant Dr. Readman has been working at the Cowles Company's works. And here we may remark that we are indebted to a paper read by Dr. Readman at the Philosophical Institution, Edinburgh, a short time ago; this paper being the third of a series which during the last year or two have been read by the same scientist on this branch of chemical industry. Here is an abstract giving a description of the plant. The works are near the Milton Station, on the North Staffordshire Railway. The boilers for generating the steam required are of the Babcock-Wilcox type, and are provided with "mechanical stokers;" the steam engine is of 600 horse power, and is a compound condensing horizontal tandem, made by Messrs. Pollitt & Wigzel, of Sowerby Bridge. The fly wheel of this engine is 20 feet in diameter, and weighs 30 tons, and is geared to the pulley of the dynamo, so that the latter makes five revolutions for each revolution of the engine by rope driving gear, consisting of eighteen ropes. The engine is an extremely fine specimen of a modern steam engine; it works so silently that a visitor standing with his back to the engine railings, at the time the engine is being started, cannot tell whether it is in motion or not.
With regard to the dynamo, the spindle is of steel, 18 feet long, with three bearings, one being placed on either side of the driving pulley. The diameter is 7 inches in the bearings and 10 inches in the part within the core. This part in the original forgings was 14 inches in diameter, and was planed longitudinally, so as to leave four projecting ribs or radial bars on which the core disks are driven, each disk having four key ways corresponding to these ribs. There are about 900 of these disks, the external diameter being 20 inches and the total length of the core 36 inches.
The armature winding consists of 128 copper bars, each 7/8 in. deep, measured radially, by 3/8 in. wide. These bars are coupled up so as to form thirty-two conductors only; this arrangement has been adopted to avoid the heating from the Foucault currents, which, with 11/2 in. conductors, would have been very considerable. The bars are coupled at the ends of the core across a certain chord and are insulated.
The commutator is 20 inches long, and has sixty-four parts. The current is collected by eight brushes mounted on a separate ring, placed concentric to the commutator; and the current is led away from these brushes by a large number of thin bands of sheet copper strapped together into convenient groups. The field magnets are of the horizontal double type.
As this machine is virtually a series wound machine, the magnet coils each consist of a few turns only of forged copper bars, 11/2 in. wide by 1 in. thick, forged to fit the magnet cores.
There is no insulation other than mica wedges to keep the bars from touching the core.
The dynamo furnishes a current of about 5,000 amperes, with an E.M.F. of 50 to 60 volts, and three years ago was claimed to be the largest machine, at least as regards quantity of current, in the world.
The current from the dynamos is led by copper bars to an enormous "cut out," calculated to fuse at 8,000 amperes. This is probably one of the largest ever designed, and consists of a framework carrying twelve lead plates, each 31/2 in. x 1/16th in. thick. A current indicator is inserted in the circuit consisting of a solenoid of nine turns. The range of this indicator is such that the center circle of 360 deg.=8,000 amperes.
The electrodes consisted of a bundle of nine carbons, each 21/2 in. in diameter, attached by casting into a head of cast iron. Each carbon weighs 20 lb, and, when new, is about 48 inches long.
The head of the electrode is screwed to the copper rods or "leads," which can be readily connected with the flexible cable supplying the current.
The electric furnaces are rectangular troughs built of fire brick, their internal dimensions being 60 in. x 20 in. x 36 in. deep. Into each end is built a cast iron tube, through which the carbon electrodes enter the furnace.
The electrodes are so arranged that it is possible by means of screwing to advance or withdraw them from the furnace.
The whole current generated by the great dynamo of the Cowles Company was passed through the furnace.
In the experiments raw materials only were used, for it was evident that it was only by the direct production of phosphorus from the native minerals which contain it, such as the phosphates of lime, magnesia, or alumina that there was any hope of superseding, in point of economy, the existing process of manufacture.
In the furnaces as used at Milton much difficulty was experienced in distributing the heat over a sufficiently wide area. So locally intense indeed was the heat within a certain zone, that all the oxygen contained in the mixture was expelled and alloys of iron, aluminum, and calcium combined with more or less silicon, and phosphorus were produced. Some of these were of an extremely interesting nature.
We now turn to a short account of the works and plant which have been erected near Wolverhampton to prove the commercial success of the new system of manufacturing phosphorus.
The ground is situated on the banks of a canal and extends to about 10 acres, which are wholly without buildings except those which have been erected for the purposes of these industrial experiments. These consist of boiler and engine houses, and large furnace sheds.
There are three Babcock & Wilcox steam boilers of 160 horse power each, and each capable of evaporating 5,000 lb. of water per hour. The water tubes are 18 ft. long x 4 inches diameter, and the steam and water drums 43 in. in diameter and 231/2 ft. long, of steel 7/16 ths. in. thick, provided with a double dead head safety valve, stop valves, blow-off cock, water gauges, and steam gauge.
The total heating surface on each boiler is 1,619 square feet and the total grate surface is 30 square feet.
The boilers are worked at 160 lb. pressure.
The engine is a triple compound one of the type supplied for torpedo boats, and built by the Yarrow Shipbuilding Company. It is fitted with a Pickering governor for constant speed. The engine is capable of delivering (with condenser) 1,200 indicated horse power, and without condenser 250 indicated horse power less.
With steam at 170 lb. pressure the engine worked at 350 revolutions per minute, but it has been rearranged so as to deliver 700 indicated horse power with 160 lb. steam pressure without condenser, and at 300 revolutions per minute:
The high pressure cylinder is 141/2 inches diameter. " intermediate " " 25 " " " low pressure " " 32 " " " stroke is 16 inches.
The dynamo for producing the requisite amount of electric current supplied to the furnaces is one of the well known Elwell-Parker type of alternating current dynamos, designed to give 400 units of electrical energy, equivalent to 536 indicated horse power.
The armature in the machine is stationary, with double insulation between the armature coils and the core, and also between the core and the frame, and is so arranged that its two halves may be readily connected in series or in parallel in accordance with the requirements of the furnaces, e.g., at an electromotive force of 80 volts it will give 5,000 amperes, and at 160 volts, 2,500 amperes when running at 300 revolutions per minute.
The exciting current of the alternator is produced by an Elwell-Parker shunt wound machine, driven direct from a pulley on the alternator shaft, and so arranged as to give 90 amperes at 250 volts when running at a speed of 800 revolutions per minute. From 60 to 70 amperes are utilized in the alternator, the remainder being available for lighting purposes (which is done through accumulators) and general experimental purposes.
The process is carried out in the following way: The raw materials, all intimately and carefully mixed together, are introduced into the furnace and the current is then turned on. Shortly afterward, indications of phosphorus make their appearance.
The vapors and gases from the furnace pass away to large copper condensers—the first of which contains hot and the second cold water—and finally pass away into the air.
As the phosphorus forms, it distills off from the mixture, and the residue forms a liquid slag at the bottom of the furnace. Fresh phosphorus yielding material is then introduced at the top. In this way the operation is a continuous one, and may be continued for days without intermission.
The charges for the furnace are made up with raw material, i.e., native phosphates without any previous chemical treatment, and the only manufactured material necessary—if such it may be called—is the carbon to effect the reduction of the ores.
The crude phosphorus obtained in the condensers is tolerably pure, and is readily refined in the usual way.
Dr. Readman and Mr. Parker have found that it is more advantageous to use a series of furnaces instead of sending the entire current through one furnace. These furnaces will each yield about 11/2 cwt. of phosphorus per day.
Analyses of the slag show that the decomposition of the raw phosphates is very perfect, for the percentage of phosphorus left in the slag seldom exceeds 1 per cent.—Chemical Trade Journal.
* * * * *
NEW BLEACHING APPARATUS.
The apparatus forming the subject of this invention was designed by Francis A. Cloudman, Erwin B. Newcomb, and Frank H. Cloudman, of Cumberland Mills, Me., and comprises a series of tanks or chests, two or more in number, through which the material to be bleached is caused to pass, being transferred from one to the next of the series in order, while the bleaching agent is caused to pass through the series of chests in the reverse order, and thus acts first and at full strength upon the materials which have previously passed through all but the last one of the series of chests and have already been subjected to the bleaching agent of less strength.
For convenience, the chest in which the material is first introduced will be called the "first of the series" and the rest numbered in the order in which the material is passed from one to the other, and it will be understood that any desired number may be used, two, however, being sufficient to carry on the process.
The invention is shown embodied in an apparatus properly constructed for treating pulp used for the manufacture of paper, and for convenience the material to be bleached will be hereinafter referred to as the pulp, although it is obvious that similar apparatus might be used for bleaching other materials, although the apparatus might have to be modified to adapt it for conveying other materials of different nature than pulp from one bleaching chest to the other and for separating out the bleaching liquid and conveying it from one chest to the other in the reverse order to that in which the material passes from one chest to the next.
The pulp material with which the apparatus herein illustrated is intended to be used is retained in suspension in the bleaching liquid and flows readily through ducts or passages provided for it in the apparatus in which the pulp to be bleached and the bleaching liquid are introduced together at the bottom of each chest and flow upward therethrough, while at the top of each chest there are two conveyors, one for carrying the pulp from one chest to the next in order, while the other carries the bleaching liquid from one tank to the next in the reverse order, the said conveyors also acting to partially separate the pulp from the liquid in which it has been suspended during its upward passage through the chest. |
|
