AND RATIO OV Tlll-:iH ATOMIC WEICiHTS. 09 



This tube took the form sliowii in Fig. 35. It was now not siife to assume 

 tliat there would be no cliange of volume on lieating to expel hydrogen. Ac- 

 cordingly, a mark was etched at e. After determining the volume of the wliole 

 tube l)y hydrostatic weighing, the volume below this mark was also determined. 

 After the expulsion of the gas, any change of volume was determined l)y immer- 

 sion to this mark. The stopcock was therefore not wet during the progress of 

 the experiment. The eflt'ect of the immersion of the stopcock during tlie pre- 

 lirainaiy woi-k of reconstructing the tube before the charging with hydi'ogeu was 

 eliminated by waiting a sufficient time before the weighing. 



One impoi'taut advantage was gained by the use of soft glass. It was now 

 possible, when the absorption was ended, to continue the current of hydrogen, by 

 breaking off the point //i of the tul)e, so as to expel any nitrogen which might 

 have accompanied the hydrogen and accumulated in the tube. After this was 

 accomplished by a current lasting three or four hours, the point was closed by 

 fusion, and the tube prepared for weighing in the same way as before. 



But a certain difficulty remained. The stopcock had to be immei'sed for at 

 least one hydrostatic weighing for each expei'iment, and this involved waiting a 

 day or two in ordei' to Ije sure that the lubrication had come again to a constant 

 state. A thii'd a|)paratus was therefore constructed, in which no stopcock was 

 used. This is the form always used aftei'wards. It has been shown in Figs. 25, 

 ■_'(■>, and 27, and its manipuhition has Ijeen sufficiently described. 



5. SYNTHESIS OF WATKi;. ArrAUATUS KOK I'liOTUK'fXfi AND WKKi IIINO AVATER. 



The apparatus in which the gases were combined and in which the water 

 produced was weighed is shown in Fig. 36. At a are two platinum jets from which 

 the gases issue into the combustion chamber. Two tubes filled with phosphorus 

 peutoxide, kept in place by rolls of asbestos, are shown at I, b. At c, e, ai-e joints 

 ground to fit corresponding joints by which the apparatus maybe connected to the 

 soui-ces of hydrogen and of oxygen. These tubes ai'e closed by fusion at d and e, 

 and notches are made whei'e they are afterwards to l)e broken oft". Wii'es /, /, 

 provide for the inflammation of the jet of hydrogen, or of oxygen, as the case 

 might be. The ends of the apparatus have hooks facilitating the hydrostatic 

 weighing which determines its volume. The whole apparatus was exhausted to a 

 ten-thousandth of an atmosphere and sealed oft from the pump at </. 



A counterpoise of suitable weight and volume was then made. Since the ap- 

 [)aratus had to be reconstructed for each experiment by providing it with new dry- 

 ing tubes, a new counterpoise had also to be made. To facilitate this, a sei-ies of 

 volumes of 50, 20, 20, 10, 5, 2, 2, and 1 cubic centimetres wei-e pi'epared and the vol- 



