of Hydrogen and some other Gases. 337 



apparatus with the hydrogen, the stop-coek k is closed, and 

 the gas contained in the bulbs m, n, and o pumped out by the 

 Graede auxiliary pump, and then the cock q is closed and h 

 opened to introduce the hydrogen into the bulbs m, n, and o. 

 When they are filled with gas the evacuation is a^ain made, 

 and then the new gas introduced. After the same process 

 has been repeated several times the cock p is finally closed 

 and the reservoirs are filled with gas till the pressure of 

 the gas reaches about 2 cm. higher than the atmospheric 

 pressure. This pressure is attained when the surface of water 

 in the cylinder b of the decomposing cell reaches the lower 

 position, as shown in fig. 8. 



To fill the measuring tube and the compressing cylinder 

 with gas, the tapered end of the latter is brought in contact 

 with the end of the delivery tube, and then the air in them 

 is pumped out. When the cock q is closed and the cock p 

 opened, the gas stored in the reservoir rushes into the 

 evacuated cylinder, filling it almost instantaneously at a 

 pressure of about one atmosphere. Next the cock k is 

 opened and new gas supplied to the reservoir, till the former 

 pressure is again attained in about 15 minutes. Thus the 

 cylinder and the measuring tube are always filled with 

 hydrogen at about one atmospheric pressure ; they are in an 

 evacuated condition only for a moment, when the communi- 

 cation to the pump is stopped by the cock q and the cock p 

 opened to introduce the gas into the cylinder. Thus any 

 diffusion of air from outside through the packings and 

 connexions is completely prevented. The same process of 

 washing the interior of the measuring tube and the com- 

 pressing cylinder with pure hydrogen is usually repeated 

 live times and the gas finally introduced into the tube and 

 the cylinder is employed for the measurement. 



The method of measurement of the mass of the hydrogen 

 was to determine the mass by replacing water in a eudiometer 

 with the hydrogen stored up at high pressure in the 

 measuring tube. If the pressure and 'temperature at the 

 time of measurement of the volume are known, then by 

 taking the vapour pressure at that temperature into con- 

 sideration, we can calculate the volume of gas at standard 

 conditions. Multiplying the density at 0° C. into the volume 

 obtained above we obtain the mass of the gas. In some 

 cases the determination of the mass of hydrogen was also 

 made by weighing and comparing the weight with the results 

 of the volumetric measurement. 



Phil. Mag. S. 6. Vol. 39. No. 231. March 1920. Z 



