7.S DENSITIES OF OXYGEN AN)> lIVDKOfiEN 



mark aiid tlie gl(il)es were rovered with ice during tlie ineasiireiuent. The tube e 

 led tu the l)aronietei', and (/ was for the admission of hydrogen. 



The vahe between the globes and the pump consisted of a U-shaped tube, /" g, 

 w liith could be tilled witli, or em[)tied of, mercury by means of the tubes and 

 stopcock shown in conncctiini with it. Sn[)pose the globes to have been exhausted 

 .iiid the pump to be ready to shut oti", the stopcock I was opened, when mereurv in 

 /• was raised by atmosplieric pressure, passing first into the vacuum in h. where any- 

 air accompanying the mei'cury would be stopped. From heie, the meicuiy passed 

 into the U tube,/' g, and filled it to near the toji of the enlargement t'. If now 

 the globes are filled with gas, its pressure will force the mercuiy up the tube y 

 leading to the pump, but leaving the U tube filled above the bend. When pressure 

 was to be measured, the stopcock I was opened, and pressure applied to the surface 

 of the mercniy in the fiask h so as to force mercury up to the mark at /. 



When it was desired to exhaust the globes again, the mercury was brought to 

 stand in the lower part of the enlargement, and the ]ioint o was cut off and replaced 

 with a tube pre[)ared to Ite closed by fusion. A Bianchi pump was coimected to 

 this and the globes were exhausted to three or four millimetres, when the connec- 

 tion was closed by fusion, leaving ihe glass as shown in the figure. The aii-pump 

 was then ap[)lied to the fiask and the stopcock ? opened, when the mercury left the 

 bend of tlie U-shaped tube free. The Toepler pump then continued tlie e.vhaustion 

 of the globes. 



■_'".». IIVDKOGEN BY NEW METHOD. SECOND .VI*I'.\H.\TUS. «AI'.A«ITV Ol' 



CONNECTINi; TUBES. 



Before the valvey'y, Fig. "Js, was fused to the tube c /, it was sealed off a little 

 below the mark /, and filled with mercury to this mark. Then the capacity of the 

 tubes between this mercury and the fusible metal plugs near the globes was deter- 

 mined just as in the previous case ; the values ol)tained have already been given 

 on page (i8. After the determination was completed, the fusible valves were 

 opened, and/"^ connected by fusion, when the apparatus was ready foi- use. 



'M). — iivi)i:o(iE.\ in S'i;\v metuok. second Ari'AKATis. uemaindei: ok the 



PROCESS. 



The rest of the process was in every respect like that in the picceding series 

 of e.\i)eriments. The only ilifferences have l)eeu noted; the pleiusure of working 

 with an a[)])aratus which could leak only by fracture was great. Several verifica- 

 tions were made of the fact that there was no ap[)reciable leakage; it will suffice 

 to give one. The a[)[)aratus was e.xhausted, and the vacuum measured with the 



