142 Professor Dewar [Marcli 27, 



reacliing low temperatures, and easy to use for cooling tubes and col- 

 lecting a few hundred c.c. of liquid air, especially if the compressed 

 air is delivered at the temperature of — 79° before expansion. With 

 larger vacuum vessels and larger regenerating coils no doubt the 

 yield of liquid could be increased. The liquid air resulting from 

 the use of this 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 Fig. 2 is used, with silver tube, about 

 -j?^ 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 atmos., showed the same appearance 

 of sudden ebullition as Cailletet had seen in his early oxygen experi- 

 ments. No sooner had the announcement been made than Olszewski 

 confirmed the result by expanding hydrogen from 190 atmos. pre- 

 viously cooled with oxygen and nitrogen boiling in vacuo. Olszewski 

 declared in 1884 that he saw colourless drops, and by partial expansion 

 to 40 atmos. the liquid hydrogen was seen by him running down the 

 tube. Wroblewski could not confirm these results, his hydrogen being 

 always what he called a " liquide dynamiqiie." 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, Cailletet, 

 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 tem- 

 perature, above which it cannot appear as liquid, is probably not 

 above — 230°." It has to be remembered that 7 per cent, of air by 

 volume in hydrogen means about 50 per cent, by weight of the mixed 

 gases. Even 1 per cent, by volume in hydrogen is equivalent to 

 some 13 per cent, by weight. 



The following table gives the theoretical temperatures reached for 



