26 ATTAINMENT OF VERY LOW TEMPERATURES. 



The hydrogen is compressed in two stages, as described on page 

 23, and first enters the water separator D where the lubrication water 

 is separated and discharged. The pipe from the cylinder D enters the 

 collecting chamber P ; the water runs into the tank Q, while the gas 

 returns to the supply pipe C. The collecting chamber is shown in detail 

 in fig. 9. 



The compressed gas, which now contains only a trace of moisture, 

 passes next through the cylinder E containing solid caustic potash, on 

 its way to the liquefier K, which in the diagram is of the type de- 

 scribed on pages 18-20. After undergoing compression, and partial 

 liquefaction, the remaining gas returns by way of the pipe L to the 

 distributing chamber P, and thence into the pipe C. Should the 

 pressure rise suddenly through the blocking of the expansion valve, 

 the cock X can be opened and some of the gas allowed to escape through 

 a pipe which enters the supply pipe C through a small cock A'^. The 

 connecting pipe S, which is of rubber, serves to prevent any waste 

 through the escape of the hydrogen which passes out of the spiral 

 opening at the bottom of the vacuum vessel H (figs. 5 or 6), when 

 the liquid hydrogen runs into the receiving vessel (p. 20). 



The operation of cooling down the liquefier has been described on 

 page 19, and need not be dealt with again here. The next step in the 

 operation was to remove the air from the compressor and purifying 

 cylinders, and this was usually accomplished by starting the com- 

 pressor two or three times, so as to take three or four cubic feet of gas 

 into it on each occasion, and then allowing the compressed hydrogen 

 to escape by opening a cock at the bottom of the potash purifier D. 

 Later it was found to be much more effective to allow the hydrogen 

 to pass completely through the apparatus and to escape at the ex- 

 pansion valve. In this case, the " washing out " of the apparatus had 

 to be completed before the cooling down was commenced. 



After washing out the apparatus the motor was again started and 

 the pressure was allowed to rise. 



Meanwhile the cap and the tap V (see page 20, fig. 5) had been re- 

 moved from the bottom of the vacuum vessel H, and the liquid air 

 was allowed to drain out of it. The collecting vessel K was now 

 placed inside the tube L (figs. 4 or 6), and the latter was placed in 

 position as shown in the figure. The connection between the tube L 

 and the brass tube h, which formed part of the gland p, was made by 

 means of a rubber sleeve s, secured to both by means of a tube of 

 copper wire. When the sleeve was in position gas could only escape 

 from the space within the tube L through the cock r, so that when the 

 latter was closed the liquid which formed in H could not flow into K. 

 When, however, the cock r was opened, liquid and gas could flow 

 from H into K, the gas passing through the cock r and the tube 5" 



