[MCLENNAN] LIQUEFACTION OF HYDROGEN 35 



coil F into the expansion coil I did so at a temperature near — 200°C. 

 The expansion valve was the same as that used in the ordinary 

 Hampson Liquéfier and the manner in which the expansion valve 

 was controlled is indicated in the diagram. 



The hydrogen which was liquefied was collected at first in the 

 base of a thin copper cylinder surrounding the expansion coil I. 

 From this it flowed into the bottom of the large silvered vacuum flask 

 surrounding the expansion coil and from there it passed into the 

 collecting vacuum flask in the lower part of S. The jacket S was kept 

 airtight at the bottom by means of a heavy circular plate carefully 

 ground to fit into the lower portion of S. This plate was held up by 

 spriilgs which were arranged to give way readily if any sudden large 

 increase of pressure was produced by explosion or otherwise within 

 the jacket S. The collecting vacuum flask was inserted or with- 

 drawn by removing the plate valve entirely. 



V. Operations 



In operating the liquéfier the whole system was first of all cooled 

 down with liquid air in the manner indicated until the thermocouples 

 attached at various points showed that a steady state was reached. 



The hydrogen compressed to about 170 atmospheres was then 

 admitted to the system with the expansion nozzle wide open until 

 the thermocouple situated close to the nozzle showed that the gas 

 was issuing from the latter at a temperature below the inversion 

 point. 



The nozzle was then throttled down and after this it was found 

 that the expansion coil was rapidly cooled to the temperature of 

 liquefying hydrogen by the expanding gas. 



VI. Results 



On April 16th the attempt to make liquid hydrogen was success- 

 ful. In all about half a gallon of it was made. During repeated 

 runs since that time tests were made to see if hydrogen containing 

 as much as one or one and a half per cent, of oxygen could be liquefied 

 by this apparatus. It was invariably found, however, that after a 

 small quantity of the liquid hydrogen had been made the expansion 

 coil choked with solid oxygen and the operations had to cease. 



With hydrogen in the cylinders at something over 99.5% purity 

 it was found that the purity attained by means of the palladiumized 



—25 



