An ingenious apparatus prevents the electricity from sparking when contact is made, so that there is no oxidation of the mercury. The mechanism is singularly beautiful, and it is quite fascinating to watch the self acting starting, stopping, inking, and printing arrangements.

We could not but admire the exquisite order in which the whole apparatus was maintained. The sides of the various glass tubes were as clean as when they were new, and the surfaces of the mercuries were as bright as looking glasses.

The university may well be proud that the instruments were entirely constructed in Stockholm by the skillful mechanic Sorrenson, though the cost is necessarily high. The meteograph, with the anemograph, cost L600, but the great advantage is that no assistant is required to sit up at night, and that all the figures wanted for climatic constants are ready tabulated without any further labor.

But the Institute is most justly celebrated for the researches on the motion and heights of clouds that have been carried on of late years under the guidance of Prof. Hildebrandsson, with the assistance of Messrs. Ekholm and Hagstroem.

The first studies were on the motion of clouds round cyclones and anticyclones; but the results are now so well known that we need not do more than mention them here.

Latterly the far more difficult subjects of cloud heights and cloud velocities have been taken up, and as the methods employed and the results that have been obtained are both novel and important, we will describe what we saw there.

We should remark, in the first instance, that the motion of the higher atmosphere is far better studied by clouds than by observations on mountain tops, for on the latter the results are always more or less influenced by the local effect of the mountain in deflecting the wind and forcing it upward.

The instrument which they employ to measure the angles from which to deduce the height of the clouds is a peculiar form of altazimuth that was originally designed by Prof. Mohn, of Christiania, for measuring the parallax of the aurora borealis. It resembles an astronomical altazimuth, but instead of a telescope it carries an open tube without any lenses. The portion corresponding to the object glass is formed by thin cross wires: and that corresponding to the eye piece by a plate of brass, pierced in the center by a small circular hole an eighth of an inch in diameter. The tube of the telescope is replaced by a lattice of brass work, so as to diminish, as far as possible, the resistance of the wind. The vertical and horizontal circles are divided decimally, and this much facilitates the reduction of the readings.

The general appearance of the instrument is well shown in the figure, which is engraved from a photograph I took of Mr. Ekholm while actually engaged in talking through a telephone to M. Hagstroem as to what portion of a cloud should be observed. The latticework tube, the cross wires in place of an object glass, and the vertical circle are very obvious, while the horizontal circle is so much end on that it can scarcely be recognized except by the tangent screw which is seen near the lower telephone.

Two such instruments are placed at the opposite extremities of a suitable base. The new base at Upsala has a length of 4,272 feet; the old one was about half the length. The result of the change has been that the mean error of a single determination of the highest clouds has been reduced from 9 to a little more than 3 per cent. of the actual height. At the same time the difficulty of identifying a particular spot on a low cloud is considerably increased. A wire is laid between the two ends of the base, and each observer is provided with two telephones—one for speaking, the other for listening. When an observation is to be taken, the conversation goes on somewhat as follows: First observer, who takes the lead—"Do you see a patch of cloud away down west?" "Yes." "Can you make out a well-marked point on the leading edge?" "Yes." "Well, then; now." At this signal both observers put down their telephones, which have hitherto engaged both their hands, begin to count fifteen seconds, and adjust their instruments to the point of cloud agreed on. At the fifteenth second they stop, read the various arcs, and the operation is complete.

But when the angles have been measured the height has to be calculated, and also the horizontal and vertical velocities of the cloud by combining the position and height at two successive measurements at a short interval. There are already well-known trigonometrical formulae for calculating all these elements, if all the observations are good; but at Upsala they do far more. Not only are the observations first controlled by forming an equation to express the condition that the two lines of sight from either end of the base should meet in a point, if the angles have been correctly measured and all bad sets rejected; but the mean errors of the rectangular co-ordinates are calculated by the method of least squares.



The whole of the calculations are combined into a series of formulae which are necessarily complicated, and even by using logarithms of addition and subtraction and one or two subsidiary tables—such as for log. sin squared([theta]/2) specially constructed for this work—the computation of each set of observations takes about twenty minutes.

Before we describe the principal results that have been attained, it may be well to compare this with the other methods which have been used to determine the height of clouds. A great deal of time and skill and money have been spent at Kew in trying to perfect the photographic method of measuring the height of clouds. Very elaborate cloud cameras, or photo-nephoscopes, have been constructed, by means of which photographs of a cloud were taken simultaneously from both ends of a suitable base. The altitude and azimuth of the center of the plate were read off by the graduated circles which were attached to the cameras; and the angular measurements of any point of cloud on the picture were calculated by proper measurements from the known center of the photographic plate. When all this is done, the result ought to be the same as if the altitude and azimuth of the point of the cloud had been taken directly by an ordinary angle measuring instrument.

It might have been thought that there would be less chance of mistaking the point of the cloud to be measured, if you had the pictures from the two ends of the base to look at leisurely than if you could only converse through a telephone with the observer at the other end of the base. But in practice it is not so. No one who has not seen such cloud photographs can realize the difficulty of identifying any point of a low cloud when seen from two stations half a mile or a whole mile apart, and for other reasons, which we will give presently, the form of a cloud is not so well defined in a photograph as it is to the naked eye.

At Kew an extremely ingenious sort of projector has been devised, which gives graphically the required height of a cloud from two simultaneous photographs at opposite ends of the same base, but it is evident that this method is capable of none of the refinements which have been applied to the Upsala measures, and that the rate of vertical ascent or descent of a cloud could hardly be determined by this method. But there is a far greater defect in the photographic method, which at present no skill can surmount.

We saw that the altazimuth employed at Upsala had no lenses. The meaning of this will be obvious to anyone who looks through an opera glass at a faint cloud. He will probably see nothing for want of contrast, and if anything of the nature of a telescope is employed, only well-defined cloud outlines can be seen at all. The same loss of light and contrast occurs with a photographic lens, and many clouds that can be seen in the sky are invisible on the ground glass of the camera. Cirrus and cirro-stratus—the very clouds we want most to observe—are always thin and indefined as regards their form and contrast against the rest of the sky, so that this defect of the method is the more unfortunate.

But even when the image of a cloud is visible on the focusing glass, it does not follow that any image will be seen in the picture. In practice, thin, high white clouds against a blue sky can rarely be taken at all, or only under exceptional circumstances of illumination. The reason seems to be that there is very little light reflected at all from a thin wisp of cirrus, and what there is must pass through an atmosphere always more or less charged with floating particles of ice or water, besides earthy dust of all kinds. The light which is scattered and diffused by all these small particles is also concentrated on the sensitive plate by the lens, and the resulting negative shows a uniform dark surface for the sky without any trace of the cloud. What image there might have been is buried in photographic fog.

In order to compare the two methods of measuring clouds, I went out one day last December at Upsala with Messrs. Ekholm and Hagstroem when they were measuring the height of some clouds. It was a dull afternoon, a low foggy stratus was driving rapidly across the sky at a low level, and through the general misty gloom of a northern winter day we could just make out some striated stripes of strato-cirrus—low cirro-stratus—between the openings in the lower cloud layer. The camera and lens that I use habitually for photographing cloud forms—not their angular height—was planted a few feet from the altazimuth with which M. Ekholm was observing, and while he was measuring the necessary angles I took a picture of the clouds. As might have been expected under the circumstances, the low dark cloud came out quite well, but there was not the faintest trace of the strato-cirrus on the negative. MM. Ekholm and Hagstroem, however, succeeded in measuring both layers of cloud, and found that the low stratus was floating at an altitude of about 2,000 feet high, while the upper strato-cirrus was driving from S. 57 deg. W. at an altitude of 19,653 feet, with a horizontal velocity of 81 and a downward velocity of 7.2 feet per second. This is a remarkable result, and shows conclusively the superiority of the altazimuth to the photographic method of measuring the heights of clouds.

Whenever opportunity occurs, measures of clouds are taken three times a day at Upsala, and it may be well to glance at the principal results that have been obtained.

The greatest height of any cloud which has yet been satisfactorily measured is only 43,800 feet, which is rather less than has usually been supposed; but the highest velocity, 112 miles an hour with a cloud at 28,000 feet, is greater than would have been expected. It may be interesting to note that the isobars when this high velocity was reported were nearly straight, and sloping toward the northwest.

The most important result which has been obtained from all the numerous measures that have been made is the fact clouds are not distributed promiscuously at all heights in the air, but that they have, on the contrary, a most decided tendency to form at three definite levels. The mean summer level of these three stories of clouds at Upsala has been found to be as follows: low clouds—stratus, cumulus, cumulo-nimbus, 2,000-6,000 feet; middle clouds—strato-cirrus and cumulo-cirrus, 12,900-15,000 feet; high clouds—cirrus, cirro-stratus, cirro-cumulus, 20,000-27,000 feet.

It would be premature at present to speculate on the physical significance of this fact, but we find the same definite layers of clouds in the tropics as in these high latitudes, and no future cloud nomenclature or cloud observations will be satisfactory which do not take the idea of these levels into account.

But the refinements of the methods employed allow the diurnal variations both of velocity and altitude to be successfully measured. The velocity observations confirm the results that have been obtained from mountain stations—that, though the general travel of the middle and higher clouds is much greater than that of the surface winds, the diurnal variation of speed at those levels is the reverse of what occurs near the ground. The greatest velocity on the earth's surface is usually about 2 p.m.; whereas the lowest rate of the upper currents is about midday.

The diurnal variation of height is remarkable, for they find at Upsala that the mean height of all varieties of clouds rises in the course of the day, and is higher between 6 and 8 in the evening than either in the early morning or at midday.

Such are the principal results that have been obtained at Upsala, and no doubt they surpass any previous work that has been done on the subject. But whenever we see good results it is worth while to pause a moment to consider the conditions under which the work has been developed, and the nature and nurture of the men by whom the research has been conducted. Scientific research is a delicate plant, that is easily nipped in the bud, but which, under certain surroundings and in a suitable moral atmosphere, develops a vigorous growth.

The Meteorological Institute of Upsala is an offshoot of the Astronomical Observatory of the university; and a university, if properly directed, can develop research which promises no immediate reward in a manner that no other body can approach.

If you want any quantity of a particular kind of calculation, or to carry on the routine of any existing work in an observatory, it is easy to go into the labor market and engage a sufficient number of accurate computers, either by time or piece work, or to find an assistant who will make observations with the regularity of clockwork.

But original research requires not only special natural aptitudes and enthusiasm to begin with, but even then will not flourish unless developed by encouragement and the identification of the worker with his work. It is rarely, except in universities, that men can be found for the highest original research. For there only are young students encouraged to come forward and interest themselves in any work for which they seem to have special aptitude.

Now, this is the history of the Upsala work. Prof. Hildebrandsson was attached as a young man to the meteorological department of the astronomical observatory, and when the study of stars and weather were separated, he obtained the second post in the new Meteorological Institute. From this his great abilities soon raised him to the directorship, which he now holds with so much credit to the university. M. Ekholm, a much younger man, has been brought up in the same manner. First as a student he showed such aptitude for the work as to be engaged as assistant; and now, as the actual observation and reduction of the cloud work is done by him and M. Hagstroem, the results are published under their names, so that they are thoroughly identified with the work.

Upsala is the center of the intellectual life of Sweden, and there, rather than at Stockholm, could men be found to carry out original research. It redounds to the credit of the university that it has so steadily supported Prof. Hildebrandsson, and that he in his turn has utilized the social and educational system by which he is surrounded to bring up assistants who can co-operate with him in a great work that brings credit both to himself, to themselves, and to the institute which they all represent.

RALPH ABERCROMBY.

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[Continued from SUPPLEMENT, No. 610, page 9744.]

[JOURNAL OF THE SOCIETY OF CHEMICAL INDUSTRY.]



NOTES OF A RECENT VISIT TO SOME OF THE PETROLEUM-PRODUCING TERRITORIES OF THE UNITED STATES AND CANADA.

BY BOVERTON REDWOOD, F.I.C., F.C.S.

CANADIAN PETROLEUM.

When I visited Canada in 1877-78, the refining of petroleum was principally conducted in the city of London, Ontario. At the present time Petrolia, Ontario, is the chief seat of the industry, and it was accordingly to this city that we made our way. Here we were treated with the greatest kindness and hospitality by Mr. John D. Noble, vice-president of the Petrolia Crude Oil and Tanking Co., and his brother, Mr. R. D'Oyley Noble, and were enabled in the short time at our disposal to visit typical portions of the producing territory and some of the principal refineries.

The development of the Canadian petroleum industry may be said to date from 1857, when a well dug for water was found to yield a considerable quantity of petroleum; but long previously, indeed from the time of the earliest settlements in the county of Lamberton, in the western part of the province of Ontario, petroleum was known to exist in Canada. In 1862 productive flowing wells were drilled at Oil Springs, but these wells, which were comparatively shallow, quickly became exhausted, and the territory was deserted on the discovery in 1865 of oil at Petrolia, seven miles to the northward, and about 16 miles southwest of the outlet of Lake Huron. Recently the Oil Springs wells have been drilled deeper, and are now producing 10,000 to 12,000 barrels (of 42 American gallons) per month. Petroleum has also been found at Bothwell, 35 miles from Oil Springs, but this district has ceased to yield. Quite recently a new territory has been discovered at Euphemia, 17 miles from Bothwell, where, at the time of our visit, there were four wells producing collectively 70 barrels per day. This territory is by some regarded as part of the Bothwell field.

The present producing oil belt extends from Petrolia in a northwesterly direction, to the township of Sarnia, and in a southeasterly direction to Oil Springs, but in the latter direction there is a break of about four and a quarter miles, commencing at a point about two miles from Petrolia. At Oil Springs there appears to be a pool about two miles square. The extension of the belt then continues in the same direction, with another break of about nine miles, to the new oil field of Euphemia, the average width of the oil belt being about two miles. In all, about 15,000 wells are believed to have been drilled in the Canadian oil fields, and of these about 2,500 are now producing, the average yield being about three quarters of a barrel per well per day. The aggregate production is probably about 700,000 barrels per annum, the greater part of which is obtained in the Petrolia district, and the stocks were at the time of our visit stated to amount to from 400,000 to 450,000 barrels.

In the Canadian oil fields the drilling contractor usually employs his own derrick, engine, boiler, and tools, furnishes wood and water, cases the well, and fixes the pump; the well owner providing the casing and pump, and subsequently erecting the permanent derrick.

The wells in the Oil Springs field were formerly from 200 ft. to 300 ft. in depth, but the oil stratum then worked became waterlogged, and the wells are now sunk to a depth of about 375 ft., and are cased to a depth of about 275 ft. to shut off the water. The contract price for drilling a 4-5/8 in. hole to a depth of about 375 ft. under the conditions mentioned is 150 dols. (L30), and the time occupied in drilling is usually about a week when the work is continued night and day. The wells in the Petrolia field have a depth of 480 ft., the contract price, including the cost of 100 ft. of wooden conductor, being 175 dols. (L35), and the time occupied in drilling being from six to twelve days. Pole tools are used in drilling, the poles being of white ash, 37 ft. in length. The derrick is about 48 ft. in height. An auger some 4 ft. in length, and about a foot in diameter, is used to bore through the earth to the bed rock, the auger being rotated by horse power.

The drilling tools commonly consist of a bit, 21/2 ft. in length by 4-5/8 in. in diameter, weighing about 60 lb.; a sinker bar, into which the bit is screwed, 30 ft. in length by 3 in. in diameter, weighing about 1,040 lb.; and the jars, inserted between the sinker bar and the poles about 6 ft. in length, and weighing 150 lb. The tools are suspended by a chain, which passes three times round the end of the walking beam and thence to the windlass, with ratchet wheel fixed on the walking beam, by means of which the tools are gradually lowered as the drilling proceeds. The cable is thus only employed in raising the tools from the well and lowering them into it.

The sand pump or bailer is frequently as much as 37 ft. in length, and is about 4 in. in diameter. The casing (4-5/8 in diameter) costs about 45 cents (1s. 101/2d.) per foot, and the 11/4 in. pump, with piping, costs from 65 dols. (L13) to 85 dols. (L17), according to the length of pipe required. An ordinary square frame derrick costs, with mud sill, from 22 dols. (L4 8s.) to 27 dols. (L5 8s.), and the walking beam about 8 dols. (L1 12s.) In many cases, however, a three-pole derrick, which can be erected at an expense of about 10 dols. (L2), is employed. A 100 barrel wooden tank costs, erected, 50 dols. (L10).

THE CANADIAN TORPEDO.

The wells are torpedoed on completion with from 8 to 10 quarts of nitroglycerine, at a cost of 4 dols. (16s.) per quart. The torpedoes employed in the Canadian oil field are much smaller than those used for a similar purpose in the United States, the tin shell being only 6 ft. in length by 3 in. in diameter. We were enabled to witness the operation of torpedoing a well, and the following particulars, based on notes taken at the time, may be of interest: The torpedo case, which was furnished with a tube or "anchor" at the lower end, 8 ft. in length, was placed in the mouth of the well and suspended so that its upper end was level with the surface of the ground. Eight quarts of nitroglycerine, which was in a tin can, was then poured into the torpedo case, and the torpedo was carefully lowered into the well, which contained at the time about 250 ft. of water, until the end of the anchor rested on the bottom of the well. A traveling primer or "go-devil squib" was then prepared as follows: A tin cone, 14 in. in length by 2 in. in diameter at the open end, was partially filled with sand to give it the necessary weight. A piece of double tape fuse, 2 ft. long, was inserted into a Nobel's treble detonator, and over the detonator and a portion of the fuse a perforated tin tube or sheath was passed. This tube was then inserted through a hole in a strip of tin fixed across the mouth of the conical cup into the sand, so that the detonator was embedded. The sand was then saturated with nitroglycerine, the fuse lighted, and the primer dropped into the well. In about 45 seconds there was a perceptible tremor of the ground, immediately followed by a slight sound of the explosion. After an interval of a second or two there was a gurgling noise, and a magnificent black fountain shot up twice as high as the derrick, upon which all the spectators ran for shelter from the impending shower of oil and water. The well not being a flowing one, the outrush was only of momentary duration, and within a few minutes the drillers were at work removing from the well, by means of the sand pump, the fragments of rock which had been detached by the explosion. On the table are specimens of this rock, which I obtained at the time.

The maximum yield per well is ten barrels per day, and the minimum yield for which it is considered profitable to pump is a quarter of a barrel per day. The yield being in some cases so small, it is usual to pump a number of wells through the agency of one engine, the various pumps being connected with the motor by means of wooden rods. In one instance I saw as many as eighty wells being thus pumped from one center. The motive power was a 70 h.p. engine, which communicated motion, similar to that of the balance wheel of a watch, to a large horizontal wheel. From this wheel six main rod lines radiated, the length of stroke of the main lines being 16 in., and the rate of movement 32 strokes per minute. Some of the wells being pumped from this center were from one-half to three-quarters of a mile distant, and altogether about eight miles of rods were employed in the pumping of the eighty wells.

The pipe line system in Canada has not been fully developed, and accordingly the well owner has to convey his oil by road to the nearest receiving station. Thus from the Euphemia oil field the oil has to be "teamed" 17 miles, to Bothwell. For the conveyance of the oil by road a long and slightly conical wooden tank or barrel, resting horizontally on a wagon, is employed. These vessels hold from eight to ten barrels of oil. The Petrolia Crude Oil and Tanking Company is the principal transporting and storing company. The storage charge is one cent (1/2d.) per barrel per month, and the delivery charge two cents per barrel. The petroleum produced in the Oil Springs field is stored separately from that obtained in the Petrolia field.

The storage takes place for the most part in large underground tanks excavated in the retentive clay. These remarkable tanks are often as much as 30 ft. in diameter by 60 ft. in depth, and hold from 5,000 to 8,000 barrels. In the construction of the tanks the alluvial soil, of which there is about 18 ft. or 20 ft. above the clay, is curbed with wood and thoroughly puddled with clay. On the completion of the excavation, the entire vertical surface is then lined with rings of pine wood, so that the upper part down to the solid clay is doubly lined. The bottom is not lined. The roof of the tank is of wood, covered with clay. The cost of such a tank is about 22 cents (11d.) per barrel, or 1,760 dols. (L363) for an 8,000 barrel tank, and the time occupied in making such a tank is about six weeks.

The crude petroleum from the Petrolia field usually has a specific gravity ranging from 0.859 to 0.877, while the specific gravity of the petroleum from the Oil Springs field ranges from 0.844 to 0.854.

The oil occurs in the corniferous limestone, and buildings constructed of this stone frequently exude petroleum in hot weather.

Canadian crude petroleum is of a black color, and possesses a very disagreeable odor, due to the presence of sulphur compounds. These characteristics are shown by the samples on the table, for some of which I am indebted to Mr. James Kerr, secretary of the Petrolia Oil Exchange.

The stills used in the process of refining the crude oil are horizontal two-flued cylinders, 30 ft. in length by 10 ft. in diameter, provided with six 2 in. vapor pipes. The charge is 260 barrels, and the following is an outline of the method of working. Assuming the still to be charged on Monday morning, heating is commenced about 7 A.M., and the naphtha begins to come over about 8 A.M. Of this product about six barrels is obtained in the case of Petrolia crude, or 71/2 barrels in the case of Oil Springs crude. The distillation of the naphtha takes from 2 to 3 hours, say till 10:30 A.M. The heat is then increased, and the distillation of the kerosene commences about noon, and continues till about 10 P.M. Of the kerosene distillate about 80 barrels are obtained. The first portion of the kerosene distillate is usually collected separately, is steamed to drive off the more volatile hydrocarbons, and is then mixed with the remainder of the kerosene distillate. The product which then commences to distill is known as tailings. This is collected separately and is redistilled. The distillation of the tailings continues till about 5 A.M. on Wednesday, by which time about 80 barrels has been obtained. Steam is then passed into the still through a perforated pipe extending to the bottom, and about 21 barrels of "gas oil" is distilled over. The additional quantity of kerosene obtained on redistilling the tailings brings up the total yield of this product to about 42 per cent. of the crude oil. The gas oil is sold for the manufacture of illuminating gas. The residue is distilled for lubricating oils and paraffin.

The agitator in which the kerosene distillate is treated commonly takes a charge of 465 barrels. To this quantity of distillate two carboys of oil of vitriol is added, and the oil and acid are agitated together for 20 minutes. The tarry acid having been allowed to settle is drawn off, and seven carboys more of acid is added. Agitation having been effected for 30 or 40 minutes, the tarry acid is removed as before. Another similar treatment with seven carboys of acid follows, and occasionally a fourth addition of acid is made. The oil is next allowed to remain at rest for an hour, any acid which settles out being drawn off, and cold (or, in winter, slightly warmed) water is allowed to pass down through the oil in fine streams, this treatment being continued, without agitation of the oil, for half an hour, or until the dark color which the oil assumed on treatment with acid is removed. The water is then drawn off, 10 barrels of solution of caustic soda (sp. gr. 15 deg. B.) is added, and agitation conducted for 15 minutes. The caustic soda solution having been drawn off, 30 barrels of a solution of litharge in caustic soda is added. This solution is made by dissolving caustic soda in water to a density of 18 deg. B. and then adding the litharge. Agitation with this solution is continued for about six hours, or until the oil is thoroughly deodorized. About 100 lb. of sublimed sulphur is then added, and the agitation is continued for another two hours. The oil having been allowed to settle all night, the litharge solution is drawn off, and the oil run into a shallow tank or "bleacher," where it is exposed to the light to improve its color, and is, if necessary, steamed to drive off the lighter hydrocarbons and raise the flashing point to the legal minimum of 95 deg. F. To raise the flashing point from 73 deg. F. to 95 deg. F. (Abel test) is stated to involve in practice a loss of 10 per cent., the burning quality of the oil being at the same time seriously impaired, and upon this ground the Ontario refiners in 1886 petitioned for a reduction of the test standard.

The average percentage yield of the various products is given in the following table:

Naphtha. 5 Kerosene. 42 Gas oil. 8 Tar. 25 Coke. 10 Loss (including water). 10 —- 100

There are a dozen petroleum refineries in Canada, and the annual outturn of kerosene is about 200,000 barrels of 45 imperial gallons per annum. The total consumption of kerosene in Canada is about 300,000 barrels, one-third of which is manufactured in the United States. The United States oil is subject to a duty of 40 cents on the package and 7-1/5 cents per imperial gallon on the contents, besides which there is an inspection fee of 30 cents per package. Of lubricating oils the outturn is from 75,000 to 100,000 barrels per annum.

The quality of Canadian kerosene has been greatly improved of late years, but notwithstanding the elaborate process of refining, the oil, though thoroughly deodorized and of good color, contains sulphur, and of course evolves sulphur compounds in its combustion.

The rules of the Petrolia Oil Exchange provide that refined kerosene shall be of the odor "locally known as inoffensive," and shall "absolutely stand the test of oxide of lead in a strong solution of caustic soda without change of color."

The "burning percentage" in the case of "Extra Refined Oil," "Water White" in color, and of specific gravity not exceeding 0.800, is required to be not less than 70; in the case of "No. 1 Refined Oil," "Prime White" in color, not less than 60; and in the case of "No. 2 Refined Oil," "Standard White" in color, to be not less than 55.

The "burning percentage" is determined by the use of a lamp thus described: "The bowl of the lamp is cylindrical, 4 in. in diameter and 23/4 in. deep, with a neck placed thereon of such a height that the top of the wick tube is 3 in. above the bowl. A sun-hinge burner is used, taking a wick 7/8 in. wide and 1/8 in. thick, and a chimney about 8 in. long." The test is conducted as follows: "The lamp bowl is filled with the oil and weighed, then lighted and turned up full flame just below the smoking point, and burned without interference till 12 oz. of the oil is consumed. The quantity consumed during the first hour and the last hour is noted." The ratio of the two quantities is the measure of the burning quality, and the percentage that the latter quantity is of the former is the "burning percentage" referred to.

* * * * *



TREES FROM A SANITARY ASPECT.

BY CHARLES ROBERTS, F.R.C.S., ETC.

As this is the usual time of the year for planting, pruning, and removing forest trees and shrubs, it is a fit time for considering the influence which trees exert on the sanitary surroundings of dwelling places. The recent parliamentary report on forestry shows that trees are now of little commercial value in this country. And we may conclude, therefore, that they are chiefly grown for picturesque effect, and for the shelter from the sun and winds which they afford.

The relation of forests to rainfall has been studied by meteorologists, but little attention has been given by medical climatologists to the share which trees take in determining local variations of climate and the sanitary condition of dwellings, notwithstanding they play as important a part as differences of soil, of which so much is said and written nowadays. This remark does not apply to large towns, where trees grow with difficulty and are comparatively few in number, and where they afford a grateful relief to the eye, shade from the sun, and to a very slight extent temper the too dry atmosphere, but to suburban and country districts, where it is the custom to bury houses in masses of foliage—a condition of things which is deemed the chief attraction, and often a necessary accompaniment, of country life.

Trees of all kinds exercise a cooling and moistening influence on the atmosphere and soil in which they grow. The extent of these conditions depends on the number of trees and whether they stand alone, in belts, or in forests; on their size, whether tall trees with branchless stems or thickets of underwood: on their species, whether deciduous or evergreen; and on the season of the year. The cooling of the air and soil is due to the evaporation of water by the leaves, which is chiefly drawn from the subsoil—not the surface—by the roots, and to the exclusion of the sun's rays from the ground, trees themselves being little susceptible of receiving and radiating heat. The moisture of the atmosphere and ground about trees is due to the collection by the leaves and branches of a considerable portion of the rainfall, the condensation of aqueous vapor by the leaves, and the obstruction offered by the foliage to evaporation from the ground beneath the trees.

The experiments of M. Fautrat show that the leafage of leaf bearing trees intercepts one-third, and that of pine trees the half, of the rainfall, which is afterward returned to the atmosphere by evaporation. On the other hand, these same leaves and branches restrain the evaporation of the water which reaches the ground, and that evaporation is nearly four times less under a mass of foliage in a forest, and two and one-third times under a mass of pines, than in the open. Moreover, trees prevent the circulation of the air by lateral wind currents and produce stagnation. Hence, as Mr. E.J. Symons has truly observed, "a lovely spot embowered in trees and embraced by hills is usually characterized by a damp, misty, cold, and stagnant atmosphere," a condition of climate which is obviously unfavorable to good health and especially favorable to the development of consumption and rheumatism, our two most prevalent diseases.

Now, if we examine the surroundings of many of our suburban villas and country houses of the better sort, we shall find them embowered in trees, and subject to all the insanitary climatic conditions just mentioned. The custom almost everywhere prevails of blocking out of view other houses, roads, etc., by belts of trees, often planted on raised mounds of earth, and surrounded by high close walls or palings, from a foolish ambition of seeming to live "quite in the country."

This is a most unwise proceeding from a sanitary point of view, and should be protested against as strongly by medical men as defective drainage and bad water supply. Many houses stand under the very drip and shadow of trees, and "the grounds" of others are inclosed by dense belts of trees and shrubs, which convert them into veritable reservoirs of damp, stagnant air, often loaded with the effluvia of decaying leaves and other garden refuse, a condition of atmosphere very injurious to health, and answerable for much of the neuralgia of a malarious kind, of which we have heard so much lately. A very slight belt of trees suffices to obstruct the lateral circulation of the air, and if the sun be also excluded the natural upward currents are also prevented.

As far back as 1695 Lancisi recognized the influence of slight belts of trees in preventing the spread of malaria in Rome, and the cold, damp, stagnant air of spaces inclosed by trees is easily demonstrated by the wet and dry bulb thermometer, or even by the ordinary sensations of the body. A dry garden, on gravel, of three acres in extent in Surrey, surrounded by trees, is generally three or four degrees colder than the open common beyond the trees; and a large pond in a pine wood twenty miles from London afforded skating for ninety consecutive days in the winter of 1885-86, while during the greater part of the time the lakes in the London parks were free from ice.

The speculative builder has more sins to answer for than the faulty construction of houses. He generally begins his operations by cutting down all the fine old trees which occupy the ground, and which from their size and isolation are more beautiful than young ones and are little likely to be injurious to health, and ends them by raising mounds and sticking into them dense belts of quick-growing trees like poplars to hide as speedily as possible the desolation of bricks and mortar he has created. It is this senseless outdoor work of the builder and his nurseryman which stands most in need of revision from time to time in suburban residences, but which rarely receives it from a silly notion, amounting to tree worship, which prohibits the cutting down of trees, no matter how injudicious may have been the planting of them in the first instance from a sanitary or picturesque point of view.

The following hints for planting and removing trees may be useful to those persons who have given little attention to the subject. A tree should not stand so near a house that, if it were to fall, it would fall on the house; or, in other words, the root should be as far from the house as the height of the tree. Belts of trees may be planted on the north and east aspects of houses, but on the east side the trees should not be so near, nor so high, as to keep the morning sun from the bedroom windows in the shorter days of the year. On the south and west aspects of houses isolated trees only should be permitted, so that there may be free access of the sunshine and the west winds to the house and grounds.

High walls and palings on these aspects are also objectionable, and should be replaced by fences, or better still open palings, especially about houses which are occupied during the fall of the leaf, and in the winter. Trees for planting near houses should be chosen in the following order: Conifers, birch, acacia, beech, oak, elm, lime, and poplar. Pine trees are the best of all trees for this purpose, as they collect the greatest amount of rainfall and permit the freest evaporation from the ground, while their branchless stems offer the least resistance to the lateral circulation of the air.

Acacias, oaks, and birches are late to burst into leaf, and therefore allow the ground to be warmed by the sun's rays in the early spring. The elm, lime, and chestnut are the least desirable kinds of trees to plant near houses, although they are the most common. They come into leaf early and cast their leaves early, so that they exclude the spring sun and do not afford much shade in the hot autumn months, when it is most required. The lime and the elm are, however, beautiful trees, and will doubtless on this account often be tolerated nearer houses than is desirable from a purely sanitary point of view.

Trees are often useful guides to the selection of residences. Numerous trees with rich foliage and a rank undergrowth of ferns or moss indicate a damp, stagnant atmosphere; while abundance of flowers and fruit imply a dry, sunny climate. Children will be healthiest where most flowers grow, and old people will live longest where our common fruits ripen best, as these conditions of vegetation indicate a climate which is least favorable to bronchitis and rheumatism. Pines and their companions, the birches, indicate a dry, rocky, sandy, or gravel soil; beeches, a dryish, chalky, or gravel soil; elms and limes, a rich and somewhat damp soil; oaks and ashes, a heavy clay soil; and poplars and willows, a low, damp, or marshy soil. Many of these are found growing together, and it is only when one species predominates in number and vigor that it is truly characteristic of the soil and that portion of the atmosphere in connection with it.

Curzon Street, Mayfair, W.—Lancet.

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SOLIDIFICATION BY PRESSURE.

M. Amagat has succeeded in solidifying various liquids, by compressing them in cylinders of bronze and steel. He has also photographed the crystals after crystallization, by means of a ray of electric light traversing the interior of the vessel by glass cones serving as panes. The stages of crystallization can be observed in this way with chloride of carbon, and it is seen that the process varies with the rapidity with which the pressure is produced. If rapidly, a sudden circlet of crystals gathers round the edge of the luminous field, and grows to the center. The pressure being continued, the field becomes obscure, then transparent. As the pressure is diminished the reverse takes place, and the liquid state is reproduced. M. Amagat finds that chloride of carbon solidifies at 19.5 deg. Cent., under a pressure of 210 atmospheres. At 22 deg. Cent., benzine crystallizes with a pressure of about 900 atmospheres.

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