422 



On the Liquefaction of Hydrogen. 



readily at the jet, and much of the latter is lost. Further, 

 since the efficiency of the regenerator-coil is dependent ou the 

 rate of transmission of heat through its walls — and this is 

 proportional to their superficial area — the maximum effect is 

 attained with a limited quantity of gas. 



To guard against blocking of the valve by the deposition 

 of solid impurities, the milled nut a is turned slowly back- 

 wards and forwards during the whole experiment. Tn the 

 valve E the screw fits so tightly into the brass cylinder con- 

 taining the jet that no gas can escape from the liquefier 

 through the steel tube c, and it is necessary at times to apply 

 some force to a. In constructing another machine 1 should 

 either place the screw on the valve-rod in the tube c about 

 two inches above the valve, or I should ease the screw in its 

 socket and place a gland round the valve-rod at the top of the 

 steel tube c. 



There appears to be no danger of the coil becoming blocked 

 through the deposition of solid matter inside it, even though 

 the hydrogen contains two or three per cent, of air and 

 perhaps traces of arseniuretted hydrogen, hydrocarbons, &c. 

 It must be remembered that within the regenerator-coil, even 

 very close to the jet, the temperature of the gas does not fall 

 below its critical point or the coil would become filled with 

 liquid, and it appears that this is not the case. Under these 

 conditions a gas is capable of holding a considerable quantity 

 of solids in solution, a phenomenon which has not been fully 

 explained; this may account for the fact mentioned above. 

 Solid impurities do, however, separate from the liquid in the 

 vacuum-vessel H, but as the liquid on its way to the vessel K 

 is obliged to pass through a piece of baize pressed down into 

 the bottom of H by a spring, it can be collected perfectly 

 clear. 



Almost immediately the valve E is opened the inside of the 

 vacuum-vessel H becomes coated with a layer of white matter, 

 which is probably solid air ; and shortly after, placing a light 

 behind the lower part of the apparatus and opening the cock r, 

 liquid is seen running in a fairly rapid stream from the nozzle 

 of H and collecting in K. The flow of the gas from the jet E 

 can then be checked, the tubes M and L lowered, and the 

 vacuum-vessel K, which is attached to a wire, withdrawn and 

 placed in another vessel containing a little liquid air. It 

 would then be possible to place another vacuum-vessel in L, 

 to restore L and M to their original positions, and to prepare 

 a further quantity of liquid hydrogen ; this has not, however, 

 been attempted. 



The apparatus which I have described, with the exception 



