144 • NEW RESEARCHES ON LIQUID AIR. 



merits. The efficiency is small, not exceeding the liquefaction of 2 to 

 5 per cent of the air passing, but it is a quick method of reaching 

 low temperatures, and easy to use for cooling tubes and collecting a 

 few hundred c. c. of liquid air, especially if the compressed air is deliv- 

 ered at the temperature of — 79° before expansion. With larger vacuum 

 vessels and larger regenerating coils, no doubt the yield of liquor could 

 be increased. The liquid air resulting from the use of tbis form of 

 apparatus contains about 50 per cent of oxygen. If the air is cooled 

 with solid carbonic acid previous to its reaching the vacuum tube coil 

 of pipe, the only change is to reduce the percentage of oxygen to 40. 

 Successive samples of liquid taken during the working had nearly the 

 same composition. If the arrangement shown in Plate VII is used, with 

 silver tube, about n, inch bore, and a foot or two coiled in upper part 

 of the vacuum vessel, liquid air containing 25 per cent of oxygen 

 is obtained. On the other hand, the percentage of oxygen can be 

 increased by a slight change in the mode of working. 



In the above experiments air is taken at the ordinary temperature, 

 which is a little above twice its critical temperature, and is partially 

 transformed in a period of time which, in my experiments, has never 

 exceeded ten minutes, simply and expeditiously into the liquid state 

 at its boiling point, — 194°, or a fall of more than 200° has been 

 effected in this short period of time. 



Experiments on hydrogen. — Wroblewski made the first conclusive 

 experiments on the liquefaction of hydrogen in January, 1884. He 

 found that the gas cooled in a tube to the boiling point of oxygen, and 

 expanded quickly from 100 to 1 atmospheres, showed the same appear- 

 ance of sudden ebullition as Cailletet had seen in his early oxygen 

 experiments. No sooner had the announcement been made than Ols- 

 zewski confirmed the result by expanding hydrogen from 190 atmos- 

 pheres previously cooled with oxygen and nitrogen boiling in vacuo. 

 Olszewski declared in 1884 that he saw colorless drops, and by partial 

 expansion to 40 atmospheres the liquid hydrogen was seen by him run- 

 ning down the tube. Wroblewski could not confirm these results, his 

 hydrogen being always what he called a "liquide dynamique." He 

 proposed to get "static" liquid hydrogen by the use of hydrogen gas 

 as a cooling agent. Professor Ramsay, in his System of Inorganic 

 Chemistry, published long after the early experiments of Pictet, Gail, 

 letet, Wroblewski, and Olszewski on the liquefaction of hydrogen had 

 been made, sums up the position of the hydrogen question in 1891 as 

 follows (p. 28) : 



It has never been condensed to the solid or liquid states. Cailletet, 

 and also Pictet, who claim to have condensed it by cooling it to a very 

 low temperature and at the same time strongly compressing it, had in 

 their hands impure gas. Its critical temperature, above which it can 

 not appear as liquid, is probably not above — 230°. 



It has to be remembered that 7 per cent of air by volume in hydro- 

 gen means about 50 per cent by weight of the mixed gases. Even 1 



