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Production of Sulphuric Acid.-According to actual returns for the year 1914, the production of sulphuric acid in the United States was 3,762,417 short tons of 50° acid, valued at $24,163,331. This is exclusive of 21,993 short tons of fuming acid, valued at $316,596, but the figures given above include by-product acid-that is, acid obtained in the smelter industry. The acid produced at copper and zinc smelters in 1914 amounted to 950,798 short tons of 50° acid, valued at $5,190,293. The entire production of acid by grades is tabulated below:

PRODUCTION OF SULPHURIC ACID IN THE UNITED STATES IN 1914 BY GRADES, IN SHORT TONS.

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Exclusive of 21,993 short tons of fuming acid, valued at $316,596.

PRODUCTION OF SULPHURIC ACID FROM COPPER AND ZINC SMELTERS IN 1913 AND 1914, IN SHORT TONS (REDUCED TO 60° BAUMÉ ACID).*

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*The acid reported to the Survey includes strengths rated at 50°, 53°, 55°, 60°, and 66° Baumé, and a small quantity of electrolyte and oleum. All strengths, with the exception of the electrolyte, have been reduced to both 50° and 60° Baumé, as given in the table.

Developments in Heating and Ventilation. A. H. BARKER. (Journal and Transactions of the Society of Engineers (Incorporated), vol. vi, No. 5.)-It is an undeniable fact that a room filled with air which, so far as chemical analysis can detect, is absolutely pure may feel very stuffy. For instance, the House of Commons, on the ventilation of which the author has experimented for many months for the Committee of the House, the air in the debating chamber is, chemically speaking, as pure as in any room in the

world. Fresh air simply pours into it in extravagant volumes. In a moderately full house there are no less than 13,000 cubic feet of air supplied per head per hour. Yet it produces, without any possible doubt, the effects which we are accustomed to think of as associated with defective ventilation-lassitude, sleepiness, infection, and so forth. Complaints are loud and quite general. A room may, on the contrary, feel fresh and sweet in which, judged by chemical. standards, the air is very bad. The author has analyzed air containing 25 volumes per 10,000 of CO, which felt as fresh as a spring morning, although 10 volumes is regarded as the extreme allowable impurity in current science. There must be some combination of chemical or physical conditions which accounts for the effect, so far as it is objective; when it is purely subjective, of course, it is impossible to analyze the effect. Nobody up to the present has ventured to specify what is that combination.

Examining X-ray Plates by Mercury-vapor Lamps. ANON. (Electrical World, vol. 65, No. 23, 1475.)-For the minute examination of details of structure in fabric many advantages are claimed for monochromatic light, since with it all rays which make up the image are brought together in the "plane" of the retina without the possibility of effects of color aberration. Hence vision becomes much "sharper." An interesting application of this advantage is in its use in hospital X-ray wards for the inspection of skiagraph negatives by the surgeons. A large installation of this kind was recently completed at the Cook County Hospital, Chicago. According to the physician in charge, much sharper inspection, and consequently better diagnosis of the faint images and shadows of the negative, is secured by the monochromatic light of the mercury arc than with the continuous-spectrum illumination formerly obtained from incandescent-filament units.

A Galvanic Cell Which Reverses its Polarity when Illuminated. A. A. C. SWINTON. (The Physical Society of London, vol. xxvii, part iii.)-If two plates-one of zinc and the other of tinned copper coated on one surface with selenium and varnished with enamel over the remainder of its surface are immersed in tap-water, the electric current through a galvanometer connected to the plates shows that in the dark the zinc is electro-positive to the selenium, while the result of light falling on the selenium is to increase the effect. If, however, instead of zinc, carbon or copper is employed for the non-coated plate, the interesting result is obtained that, while the selenium proves to be electro-positive to the carbon or copper in the dark, it immediately becomes electro-negative to carbon or copper the moment it is illuminated, this being easily shown by the deflections of the galvanometer in contrary directions as the light is turned on or off.

The Distribution of Heat in the Cylinder of a Gas Engine. A. H. GIBSON and W. J. WALKER. (The Journal of the Institution of Mechanical Engineers, No. 5, 1915.)—The paper deals with the results of a series of experiments on heat-flow in a gas-engine cylinder as affected by the variation of speed, load, compression ratio, and gas mixture. The principal point under investigation was to determine the effect of turbulence on this heat-flow. The trials were carried out on a "National" gas-engine of 30 b.h.p., peculiarly well suited for the investigation, a special water-jacketing arrangement being provided whereby exhaust and barrel heat losses are separated. Some 130 trials were carried out. The most important points brought out in the investigation may be summarized as follows: The mechanical efficiency (1) diminishes as the ratio air: gas increases, (2) diminishes as the speed increases, (3) is sensibly independent of compression ratio. The thermal efficiency, measured on the indicated horse-power, (1) attains a maximum with an air gas mixture of about 10:1; (2) diminishes as the speed increases. Percentage exhaust losses (including heat to exhaust-valve jacket) (1) diminished as the load increases; (2) diminish very slightly as the ratio air: gas increases; (3) increase as speed increases; (4) increase as the compression ratio increases. Percentage jacket losses (barrel and breech only) (1) increase with the load; (2) diminish as the ratio air: gas increases; (3) diminish as the speed increases; (4) are sensibly independent of compression ratio. It is interesting to note that the rate at which heat is lost to the barrel-jacket is much greater at high speeds than at low speeds, notwithstanding the lower explosion temperatures which accompany the higher speeds. This effect is apparently due to the predominating influence of turbulence, causing an increase in the effective conductivity of the working fluid. The final portion of the paper describes how heat balance sheets were made up to the end of expansion for each test by obtaining the internal energy of the fluid at the end of expansion. An interesting point brought out by these balance-sheets appears in the fact that with ordinary mixtures and compression ratios they agree very well with those of the ordinary commercial type of engine, obtained by measuring the i.h.p. and jacket heat and estimating exhaust losses by difference. For fairly rich mixtures and lower compression ratios, however, the agreement is not so good, the jacket losses as usually measured in an ordinary engine always being in excess of those more correctly computed from the internal energy of the gas.

Noise in Gearing. ANON. (English Mechanic, vol. ci, No. 2616, 325.) It is not always easy to trace noise to its source, for it is often the combined effect of several small individual causes, and not infrequently an incorrect conclusion is reached and a wrong remedy applied. Two manufacturers, both producing a similar machine, claim to have minimized noise by entirely opposite means, both main

taining their own solution the best possible. One had adopted an extra-long tooth, the other an extra-short tooth. The author points out that the most prolific cause of noise is inaccuracy of workmanship, both in the gears themselves and in their mounting. He describes at considerable length precaution to be observed in attaining accuracy essential to good results, whatever be the form of tooth adopted or the material.

The Second Pan-American Scientific Congress.-During the present year two important Pan-American gatherings convene in Washington under the auspices of the Government of the United States. The first of these, the Pan-American Financial Conference, occurred the week of May 24, 1915. Of greater interest to the educational world, however, is the Scientific Congress that will convene in Washington, beginning December 27, 1915, concluding its sessions January 8, 1916. The first congress of this name was held in Santiago, Chile, in 1908. This congress was well attended by visiting delegates from the United States. On its adjournment, entirely unsolicited on the part of the latter, Washington was designated as the place of meeting of the second congress. The Scientific Congress will concern itself with the constructive discussion of the grave economic problems with which the western hemisphere has been confronted by the war in Europe that invite the serious attention of scientists and experts in the various fields of applied science, as well as with advances in the domain of pure science made since the last congress in Santiago, Chile. Science is comprehensively defined by the congress, and includes, authropology, astronomy, agriculture, education, engineering, jurisprudence, chemistry, medical science, and commerce. The significance of the congress through the importance of the above subjects is greatly enhanced through the international reputation of the persons chosen to arrange for the program of the different sections of the congress, most of whom have an intimate first-hand acquaintance as well with the local resources, development, and scientific interest in the various LatinAmerican countries.

PRESS OF

J. B. LIPPINCOTT COMPANY
PHILADELPHIA

THE FRANKLIN INSTITUTE

ANNOUNCEMENTS

MEETINGS

COMMITTEE ON SCIENCE AND THE ARTS. First Wednesday of each month, 8 P.M. (except July and August).

BOARD OF MANAGERS. Second Wednesday of each month, 3.30 P.M.

INSTITUTE. Third Wednesday of each month (except June, July, August and September), 8 P.M.

SECTION MEETINGS. Thursday Evenings (except week of Institute Meeting) 8 o'clock. October 1 to April 30.

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