

so DENSITIES OF OXYGEN AND HYDROGEN 



The voltameter was tilled with sodium hydroxide which had been made from 

 clean sodium ; it was freed from carbon dioxide with barium hydroxide. The sto[)- 

 cock d was never turned except once to open and once to close for each experiment, 

 anil was lul)ricated often ; it is thought that it ilid not leak, as tin- pressure t>n the 

 two sides of the kev was alwavs nearly the same durinir the times w hen leakaire 

 miglit cause crioi-. The legulation ot" the current required to maintain a [U'essure 

 ecpial to that of the atmosphere was obtained, not from this stopcock on the volta- 

 meter, but fiom the one mentioned before, which was innnersed in sulphuric aciil. 



For some experiments the stopcock of the voltameter was leplaced by a fusible 

 metal valve. The opening it by fusion is simple ; but when it is to be closed, the 

 metal has to be [)ushed into its place in the constricted part of the glass tube. 

 When this has to be done without opening the tube to the atmosphere, the manipu- 

 lation is accomplished by introducing into the tube an iron instrument wdiich is 

 moved by a current in a helix enclosing the tube. 



5. DKNsnY OF KLKCTKOLYTIC GAS. FILLING GLOBES Wllil IHi: Ml.\i:il GASKS. 



AN'heii a curient had been passed through the voltameter for a few days, it was 

 closed, wiped, and weighed against a counterpoise of etpnd volume and nearly 

 e(pial weight. When the weights retpiired had been learned, the tw^) volumes on 

 thi' opposite pans of the balance were made very nearly ecpial, exactly :is described 

 at page 48. 



After tile weighinir, the voltameter was set in a tank of water and ice. A 

 ground joint was fitted to that of the voltameter, shown in Fig. .'51 at c, and then 

 fused to the stopcock which was attached to the globes, as shown at e, Fi<4. "_".». 

 The tube /"was now connected to the air-pump and a three-Avay stopcock, and the 

 volume included between A, Fig. 29, and d. Fig. 31, was detei'mined, exactly as the 

 volume of the tubes connecting the arlobes to the barometer had been detei'mined 

 (page 67). This space was finally exhausted and sealed off. The stopcock d. Fig. 

 .'51, was then opened, and y. Fig. '29, was closed. The passage through //, Fig. i?9, 

 was now opened by fusion, a curi-ent was passed through the voltametei-, and the 

 passage of the gas into the globes was regulated by the stopcock till the globes 

 were filled. The pressui-e in the voltameter was kept very nearly constant. The 

 filling the globes took about thi'ee hours and thi-ee (juarters. 



<). DKNsnV OK KLKC'inoLYTIC GAS. .MEASUUKSIKNT Ol' rRESSUllK. 



The measurement of pressure of the gas was iiuide exactly as in the Ciuse of 

 hytb'ogeii, except that the tube for admitting the gas was not now closed by fusion, 

 and that therefore a different method of beiufj .safe amiinst leakaare was needed. 



