THE COMPOSITION OK WATKI;. HYDROGEN 137 



very low temperature, and then allowed them to expand, either by 

 directly decreasing the pressure or by allowing them to escape into the 

 air, by which means the temperature fell still lower, and then, just as 

 steam when rapidly rarefied 3 - deposits liquid water in the form of a 



pressed the gas (;lt il pressure of 4-6 atmospheres) and forced it into the tube K, 

 vigorously cooled by being surrounded by boiling liquid sulphurous anhydride, which 

 was condensed in the tube C by the pump B, and rarefied by the pump A. The 

 liquefied carbonic anhydride flowed down the tube K into the tube H, in which it was 

 subjected to a low pressure by the pump E, and thus gave a very low temperature of 

 about 140. The pump E carried off the vapour of the carbonic anhydride, and conducted it 

 to the pump F, by which it was again liquefied. The carbonic anhydride thus made an 

 entire circuit that is, it passed from a rarefied vapour of small tension and low tempera- 

 ture into a compressed and cooled gas, which was transformed into a liquid, which 

 again vaporised and produced a low temperature. 



Inside the wide inclined tube H, where the carbonic acid evaporated, was placed a 

 second and narrow tube M containing hydrogen, which was evolved in the vessels L 

 from a mixture of sodium formate and caustic soda (CHOoNa + NaHO^Na^COs + Ho). 

 This mixture gives hydrogen on heating the vessel L. This vessel and the tube M were 

 made of thick copper, and could withstand great pressures. They were, besides, her- 

 metically connected together and closed up. Thus the hydrogen which was evolved had 

 no outlet, accumulated in a limited space, and its pressure increased in proportion to 

 the amount of it evolved. The magnitude of this pressure was recorded on a metallic 

 manometer E attached to the end of the tube M. As the hydrogen in this tube was sub- 

 mitted to a very low temperature and a powerful pressure, there were all the necessary con- 

 ditions for its liquefaction. When the pressure in the tube H became steady i.e., when 

 the temperature had fallen to 140 J , and the manometer R indicated a pressure of 650 

 atmospheres in the tube M then this pressure did not rise with a further evolution of 

 hydrogen in the vessel L. This served as an indication that the tension of the vapour of 

 the hydrogen had attained a maximum corresponding with 140, and that consequently 

 all the excess of the gas was condensed to a liquid. Pictet convinced himself of this 

 by opening the cock N, when the liquid hydrogen rushed out from the orifice. But, on 

 leaving a space where the pressure was equal to 650 atmospheres, and coming into contact 

 with air under the ordinary pressure, the liquid or powerfully-compressed hydrogen 

 expanded, began to boil, absorbed still more heat, and became still colder. In doing so 

 a portion of the liquid hydrogen, according to Pictet, passed into a solid state, and did 

 not fall in drops into a vessel placed under the outlet N, but as pieces of solid matter, 

 which struck against the sides of the vessel like shot and immediately vaporised. 

 Thus, although it was impossible to see and keep the liquefied hydrogen, still it was 

 admitted that it passed not only into a liquid, but also into a solid, state, because Pictet 

 in his experiments obtained other gases which had not previously been liquefied, 

 especially oxygen and nitrogen, in a liquid and solid state. Pictet supposed that liquid 

 and solid hydrogen have the properties of a metal, like iron. 



3 - At the same time (1879) as Pictet was working on the liquefaction of gases in 

 Switzerland, Cailletet, in Paris, was occupied en the same subject, and his results, 

 air hough not so convincing as Pictet's, still showed that the majority of gases, previously 

 unliquefied, were capable of passing into a liquid state. Cailletet subjected gases to a 

 pressure of several hundred atmospheres in thin glass tubes (fig. 25) ; he then cooled 

 the compressed gas as far as possible by surrounding it with a freezing mixture; a 

 cock was then rapidly opened for the outlet of mercury from the tube containing the gas, 

 which consequently rapidly and vigorously expanded. This rapid expansion of the gas 

 would produce great cold, just as the rapid compression of a gas evolves heat and causes 

 a rise in temperature. This cold was produced at the expense of the gas itself, for in 

 rapidly expanding its particles were not able to absorb heat from the walls of the 

 tube, and in cooling a portion of the expanding gas was transformed into liquid. This 



