( 167 ) 



siphon over, this stopper is removed and the inflow tube Pb (PI. I) 

 is connected with the siphon-tube h (fig. 2) with a piece of india 

 rubber tubing. To prevent breaking of the india rubber, which through 

 the cold has become brittle, the new-silver tubes are arranged so 

 that thej fit into each other, hence the india rubber is not strained 

 so much. 



The admission of liquid air into the refrigerator vessel is further 

 regulated with the cock P, PI. I. When the float indicates that the 

 reservoir is almost empty, another reservoir is put in its place. 



The cock Ks is regulated according to the readings on the 

 mercnry manometer tube Y. 



b. The air is caused to evaporate at a pressure of 15 mm., which 

 is possible because a BuRCKHARDT-WEiss-pump % PI. II is used as 

 vacuumpump. 



The vacuumpump is the same as that used in measurements with 

 the cryostat containing a bath at — 217° (comp. Comm. No. 94^^ June '05) 

 and has been arranged to this end as described in Comm. No. 83 

 V. March '03. The letters at S on PL II have the same meaning as 

 on PL VIII of Comm. N". 83. As has been described in Comm. 

 No. 94^ VIII, June '05, this vacuumpump ?5, displacing 360 M' per 

 hour, is exhausted by a small vacuumpump, displacing 20 M' per hour^) 

 (indicated by ^ on PL II). 



§ 5. How the Viquefactor is set ivorking. 



a. When the apparatus is filled with pure hydrogen, as described 

 in § 2, and when air evaporating under low pressure is let into the 

 refrigerator, for convenience the hydrogen, admitted through Q) and -^ 

 PL II along Kc, is caused to stream through during some time 

 with wide open cock il/, PL I, for the forecooling of the whole 

 apparatus. Then the cock M is regulated so that the pressure in 

 the regenerator spiral rises slowly. It is quite possible for the appa- 

 ratus to deliver liquid hydrogen at 100 atm., it has done so at 70 atm. 

 As a rule, however, the pressure is kept between 180 and 200 atm. 

 because then the efficiency is some times larger ^). The liquefactor 

 then delivers about 4 liters liquid hydrogen per hour. Part of the 

 hydrogen is allowed to escape along Kha PL I fig. 2 [Kd PL II) 

 for the forecooling of the siphon N^^ PL I and the cock N, 



As soon as liquid hydrogen begins to separate we perceive that the 



1) When we use oxygen (comp. § 2 note 2), and a pressure as low as a 

 few mm should be required, forecooling is required in the second refrigerator 

 like F, where oxygen evaporates under low pressure, for instance towards j?. 



2) V. D. Waals has shown the way how to compute this (comp. note 1 § 2). 



12* 



