Liquefaction of Hydrogen. 419 



passes into a vessel tilled with water and so acts as a safety- 

 valve ; there is also a stoneware cock at the bottom for 

 drawing off spent acid. When all the air has been expelled 

 from the cask the gas, after passing through a wash- bottle 

 tilled with a solution of potassium permanganate, is allowed 

 to enter the gasometer. The latter is thoroughly icashed out 

 with hydrogen before the main quantity is collected. The 

 preparation of the hydrogen occupies five hours. 



The general arrangement of the plant for the compression 

 of the hydrogen, which is carried through the pipe NN to the 

 cock and temporary communication made by means of a lead 

 pipe cr with two screw- anions, is shown in text-fig. 1. The 

 hydrogen, or air when the latter is to be liquefied, is first of 

 all taken into the low-pressure cylinder /3 of the compressor, 

 which is driven by a 5-horse-power motor, and passes thence 

 through the coil, kept cool by a current of water which 

 circulates through the tanks surrounding the cylinders and 

 coils, and enters the high-pressure cylinder through the 

 tube 8 under a pressure of about 16 atmospheres. A small 

 quantity of a mixture of glycerol and water containing 5 per 

 cent, of caustic soda is taken into the low-pressure cylinder 

 together with the gas. The mixture is contained in the 

 vessel 7], and the flow is controlled by the glass stopcock and 

 arrangement shown in the figure. In the second cylinder 

 the pressure is raised to about 200 atmospheres, and the gas, 

 after passing through the coil co, enters the cylinder /jl, in 

 which the water used in lubricating the cylinders is separated 

 and expelled through the cock k. This water, together with 

 a little gas, passes along the tube u and enters the cylinder P: 

 the water flows into the tank e, and the gas, during the com- 

 pression of the hydrogen, is allowed to return to the gasometer 

 through the cock i. The details of this apparatus have already 

 been given. 



The gas from /j, passes into the cylinder X, which contains 

 lumps of solid caustic potash to remove traces of moisture or 

 of other impurities. This cylinder is employed in compressing 

 both air and hydrogen, and can be connected by the tube t 

 either with a Hampson air-liquefier or, as in the figure, with 

 the coil A of the liquid-hydrogen apparatus. The tube Talso 

 communicates with a gauge and with a cock, through which, 

 if the pressure becomes too high, the excess of gas may be 

 allowed to escape into the pipe NN connecting the gasometer 

 and the compressor. The liquefier, of which the detail has 

 already been given, does not require further description. It 

 is sufficient to state that the gas, after passing through the 

 coils enclosed in Q and L, expands at a valve within L 



