182 On the Formation of Solids at Low Temperatures. [Feb. 4 r 



a 



In investigating solid hydrogen the apparatus shown in the accom- 

 panying figure was employed. The liquid hydrogen was introduced 

 into a small clear-glass vacuum-vessel 15 cm. long and 4 cm. in 

 internal diameter. This vessel was placed inside a glass tube BB, 

 which communicated with an exhaust pump 

 through a tube DD sealed to it, and was closed by 

 a rubber stopper C. A short glass tube E, 6 mm. 

 in diameter, passed through the stopper, and 

 through it passed the stirring rod FF. To allow of 

 free rotating motion to the stirrer, and to make the 

 apparatus gas-tight, a short piece of rubber tube 

 G, was passed over the end of the tube E and was 

 wired to F. The lower part of the apparatus was 

 contained within the vacuum vessel H, which 

 contained a small quantity of liquid air. 



When the liquid hydrogen was made to boil in 

 vacuo, its temperature fell, but the liquid did not 

 appear to become more viscous. At length films 

 of a colourless glassy substance formed at the 

 surface, and broke away as the bubbles rose. After 

 a short time the vessel became filled with these 

 flakes, and while in this condition stirring, by 

 giving the top of the rod F a rotatory motion, did 

 not appear to indicate that the portion which 

 remained liquid had undergone any considerable 

 increase in viscosity. After a time the mass con- 

 tained so much solid that it became pasty, and 

 finally the whole of it appeared fairly homo- 

 geneous. 



DVk\^JJ li The solid evaporated fairly rapidly, so that after 



about 10 minutes only a hollow cylinder of it, 

 about 3 cm. long and 2*5 cm. in diameter, re- 

 mained. This had the appearance of a film of ice 

 which had partly thawed, consisting of clear granules connected by 

 thinner and less transparent portions of solid. No crystals were 

 observed on either of the three occasions on which the experiments 

 was carried out. An attempt was made to examine the solid in the 

 field of a polariscope, but it was unsuccessful. 



Though there is no direct evidence of the formation of crystalline 

 hydrogen, my experiments lead me to the belief that solid hydrogen is 

 a crystalline substance and not a pseudo-solid. The sharpness with 

 which the solid hydrogen is formed, and the constancy of the apparent 

 melting pressure, are distinct evidence in favour of this conclusion, 

 though it must be allowed that the rate of change in viscosity, when 

 the temperatures are measured on the Centigrade scale, will probably 



