The Optical Magic Lantern Journal (August 1894)

134 The Optical Magic Lantern Journal and Photographic Enlarger. The Supply of Oxygen to Lantern Flames.—No. IIl. By W. H. Harrison. Some researches were afterwards made on the same subject by Dr. J. W. Draper, of New York, to whose records I have not access at the present moment, but will try to find them a few days hence, ~ Lhe late Professor Graham investigated the subject scientifically at a later date, and communicated the results to the Royal Society. His paper was entitled, “The absorption and dialytic separation of gases by colloid septa,” and was published in part by that Society in ‘‘ Philosophical Transactions.” Several parts were struck out in pencil from the author’s manuscript, so that Professor Graham's full acknowledgment of the earlier work on the subject performed by Dr. Mitchell and Dr. Draper, did not appear in ‘‘ Philosophical Transactions ” with the rest of the memoir in 1866, The paper in full, free from these excisions, will be found in ‘‘ Chemical and Physical Researches, by Thomas Graham, F.R.S., collected and printed for presentation only. Preface and analytical contents by Dr. Angus Smith, Edinburgh, 1876." Graham said in the paper: ‘“‘The penetration of rubber by gases may be illustrated by their passage into a vacuum, as well as into an atmosphere of another gas, in the old experiments of Dr. Mitchell” ; but, as we have already seen, Dr. Mitchell did experiment upon the passage into a vacuum, as in the case of the column of mercury in an inverted vessel over a mercury trough. Professor Graham then describes practically the same arrangement, but somewhat modified; he used a glass tube closed at its upper end by a thin plate of stucco, to support the film of indiarubber fixed over the top; the only difference is the insertion of the stucco. The way in which Graham fixed the edges of the india-rubber film, was to bind them round with copper wire and to cement them at the edges in contact with the glass, with gutta percha softened by heat. With the barometer and thermometer at invarying heights, he found the following to be the rates of penetration of rubber by equal volumes of gas :— : , Time. Carbonic Acid 1:000 Hydrogen .. +. 2470 Oxygen a ei -65316 Marsh Gas (CH,) .. +» 6325 Atmospheric Air .. 11-850 Carbonic Oxide 12-203 Nitrogen .. 13°585 Graham found excessively thin films of rubber to be efficient for the purpose, and used one but slightly over a two-thousandth part of an inch thick. He says: ‘Such a film of rubber appears to have no porosity, and to resemble a film of liquid in its relation to gases—differing entirely in this respect from a thin sheet of paper, graphite, earthenware, or even gutta percha, as will appear hereafter.’ He also pointed out that the phenomena of gaseous penetration are due to each gas becoming liquid inside the rubber film, and then evaporating upon the other side. He found that the rubber film becomes more permeable to gases as the temperature rises, . within a certain range; it renders the’ rubber | softer and more like a liquid. This was distinctly observed in operating with silk cloth varnished on one side with rubber, which was penetrated by the air from the atmosphere, passing into a vacuum at the following rates per square metre of surface :— At 4°C, by 0°56 cubic ceutim. of air in 1 minute, » 14°C, by 225, , », 60° C, by 6:63 ” a a 7 With a colloid septum properly supported over a vacuous space, as the velocities of nitrogen and oxygen passing separately had been observed to be as 1 to 2°556, the mixed gases found on the other side, should, according to calculation, consist of 40-46 oxygen and 59:54 nitrogen, in 100 volumes. With the apparatus Graham used, he found 42:53 of oxygen in the dialysed air. He next tried experiments on a more extensive scale, by the use of a Sprengel pump with its joints well closed, in the manner specified by Dr. Sprengel. Using a common elastic carriage bag, measuring 18 in. by 16 in., made of india-rubber between double cotton cloth vulcanized, one cubic inch of air was drawn through in an hour, or at the rate of nearly three cubic inches per hour for one metre of cloth ; the air contained close upon 40 per cent. of oxygen. Next he tried four yards of vulcanized india-rubber tubing, closed at one end, and the rate of penetration was found to be one-fifth of that of the previously used rubber cloth. Then he tried thin sheet rubber, not vulcanized ; it was one millimetre in thickness, and made into a bag having a total surface of 231 square inches; a double thickness of felted carpet was placed inside the folds of the rubber to keep the sides apart. Of the dialysed air, 11°45 cubic. centimetres were collected in four hours, containing 41:48 per cent. of oxygen, with a sensible trace of carbonic acid. From a larger bag of thin sheet rubber, with a surface of 640 square inches, and its sides distended ” ”