138 



NA TURE 



[July 28, 1923 



diagram. It passed successively through the coils Di, 

 Dj and D3, D4 arranged in parallel. Ii then entered 



I'l.U. 4. Helium liqueficr (;is instaHed). 



the coils Pj and Po also in parallel, and afterwards 

 passed successively through the coils P3, P4 and Pg. 

 The coils Dg, D4, Pj and Pg 

 were cooled by the cold hydro- 

 gen vapour as it was drawn off 

 by the hydrogen vacuum pump, 

 and the coils Dj, D3, Pg and Pg 

 by the expanded helium that 

 issued from the region about 

 the expansion valve on the way 

 to the gasometer. The coil P^ 

 served for the final pre-cooling 

 of the compressed helium and 

 was immersed in liquid hydro- 

 gen boiling under a pressure of 

 6 cm. of mercury. A trap T 

 was provided, by means of 

 which the gas was freed from 

 the last traces of oil or water 

 vapour from the compressor. 

 The tubes B^ were made of 

 copper and were filled with 

 cocoanut charcoal. They were 

 cooled with liquid air during 

 the liquefaction process with a 

 view of absorbing any gaseous 

 contamination introduced dur- 

 ing the operation of the cycle. 



gas thermometers with reservoirs at M and Mj, that 

 were connected with a mercury manometer by fine sieel 

 tubing G2. 



The liquid hydrogen from large vacuum-surrounded 

 metal containers was first transferred to the unsilvered 

 flask Fi, that was protected by an outer silvered 

 flask Fg containing liquid air. This flask Fj was 

 provided with two unsilvered vertical observation 

 strips, one on either side, so that the level of the liquid 

 hydrogen in Fj could be seen directly. The valve C^ 

 controlled the intake of the liquid hydrogen from Fj 

 to the refrigerator, and the valve C^ with its corre- 

 sponding spindle controlled the expansion nozzle at 

 the bottom of the coil P^. The efficiency of the 

 regeneration properties of the expansion coil Pj was 

 assured by fitting closely over it a very thin german- 

 silver envelope soldered at X to the bottom of the 

 german-silver liquid hydrogen container. With this 

 arrangement the expanded helium was forced to go 

 through the interstices of the expansion coil in order 

 to enter the holes H in the tube surrounding the 

 expansion valve spindle. 



The temperature of the region beneath the expansion 

 nozzle was determined with a helium gas thermometer 

 provided with a german-sih-er reservoir at Mg and a 

 connecting steel capillary tube Gj. The protecting 

 vacuum flask Fg was provided with a specially designed 

 siphon tube P. This tube was double-walled and was 

 protected by silvering and by an intervening vacuum 

 in the same manner as a Dewar flask. The flask F4 

 could be made either totally silvered or partially 

 silvered with a plain portion at the bottom. In the 

 latter case it was protected by a plain vacuum flask 

 containing liquid hydrogen, and this in turn by a plain 

 vacuum flask containing liquid air. 



Fig. 5.-Metal container for liquid air. fic 6.— Metal container for liquid hydrogen. 



Thei-e figures illustrate the types of metallic vacuum Dewar Fl.-isks found useful in handling large 

 quantities of liquid air and liquid hydrogen. They were made of polished spun copper. In assembhng them, 

 extreme precautions, it was found, had to be taken to remove not only the air but also all water vapour from 

 The level of the liquid hydrogen the space between the spherical surfaces. A container of 25 litres capacity when well constructed did not 

 , , . ' •'P. lose so much as a kilogram of liquid air per day. 



m the refrigerator surrounding 



the - coil P4 was determined by means of copper- 

 constantan thermo-couples, and alternatively by helium 



NO. 2804, VOL. I 12] 



In constructing the hydrogen and helium liquefiers 

 great care was taken to see that all the complicated 



