420 Dr. M. W. Travers on the 



controlled by the milled nut a, and finally returns by the tubes 

 ■G> w, and R and the stopcock i to the tube N. 



The loss of gas during each experiment amounts to about 

 10 per cent, of the whole; and since air and other gases of 

 higher boiling-point separate as solids in the vacuum-vessel H, 

 the gas becomes purer each time it is used. 



During the two or three days immediately preceding an 

 experiment, the compressor is employed in producing liquid 

 air. For this purpose we use a Sampson liquefier, which is 

 capable of yielding about 1*25 litres of the liquid per hour. 

 The liquid air is stored in vacuum-vessels capable of holding- 

 altogether about 8 litres; comparatively little loss occurs 

 through evaporation, and the vessels are usually filled up on 

 the last morning. After preparing the liquid air it is advis- 

 able to take the compressor to pieces and carefully inspect 

 the valves, springs, and fibre packings. In the meantime the 

 Hampson machine is removed, the connexions are made 

 between the potash cylinder and the hydrogen liquefier, and 

 the lead pipe connecting the supply-pipe NN with the intake 

 of the compressor is placed in position. 



The actual experiment requires four persons. One controls 

 the valves a and b ; the second attends to the compressor, 

 regulates the escape of the water from the cylinder //,, and 

 opens or closes the cock x as the pressure rises or falls; the 

 third sees that the vessel in which the coil A is immersed 

 contains sufficient solid carbon dioxide; the fourth hands the 

 vacuum- vessels of liquid air as they are required. 



The first step in the operation is to cool the liquefier to the 

 temperature of liquid air. Liquid air is first poured into the 

 chamber B, and thence flows into C by connecting it with 

 the exhaust-pump through the cock £ and turning the valve b; 

 when C is partially filled and the vacuum-gauge indicates that 

 the liquid air is not evaporating at a great rate, the valve b is 

 closed and the cock t is turned so as to cut off the exhaust and 

 leave the chamber open to the atmosphere (p. 414). 



The vacuum-vessel M and the tube L with the vacuum- 

 vessel it contains are removed by rolling up the rubber sleeve s 

 on to the tube h and lowering the cradle in which M is sus- 

 pended. The rubber cap carrying the tap v is then fitted to 

 the nozzle of H and connected with a rubber tube dipping 

 into a vacuum-vessel filled with liquid air. 



The escape-pipe G, from which the rubber tube has already 

 been removed and replaced by a rubber cork, is now connected 

 with the exhaust-pump through the cock v. Liquid air is 

 drawn into the vacuum-vessel H, and on closing the stopcock V 

 boils under reduced pressure, cooling the regenerator-coil to 



