56 



ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



in a vacuum before weighing. It is true that Stas has shown that 

 amnionic chloride sublimed in a vacuum gave the same equivalent 

 referred to the silver as preparations sublimed in air ; but this choice 

 of ammonic chloride had the disadvantage that its two dissociation 

 products possess different rates of diffusion, and moreover his silver had 

 not been fused in a vacuum as ours had been. The data and results 

 are given below. 



The ratio of sodic chloride to silver ; doth substances fused in a vacuum. 



These experiments show that probably not enough gas is absorbed 

 during fusion of the salt in air sensibly to alter the apparent combining 

 weight. It is true that gases easily remain in supersaturated solution 

 in liquids, and that long-continued relief from pressure is necessary to 

 remove them ; but fused sodic chloride is so mobile and possesses so low 

 a density as to make the retention of much gas very unlikely. That air 

 may be adsorbed by the cold salt is of course highly probable, but the 

 surface of a fused lump is so small that the weight of this adsorbed 

 air must be negligible. One would here expect a lower result from 

 the salt fused in a vacuum, if gas were dissolved in the other ex- 

 periments, but the results were in fact slightly higher, although not 

 beyond the probable limit of experimental error. It appeared from 

 tests with indicators that the salt remained strictly neutral after fusion 

 in a vacuum, as it did in the air. 



Being unable to conceive of any other sensible inaccuracies which 

 could affect the analyses of the chloride of sodium, we turned our 

 attention next to the composition of the chloride of silver, because of 

 the before- mentioned suspicion that Stas was here also in error. An 

 additional reason for this revision is found in the fact that this atomic 

 weight of iodine, found at about the same time, has been found to be 

 about 0.1 per cent too low.* 



*Ladenburg, Berichte d. d. chem. Gesell., 35, 2275. Scott, Proc. Chem. Soc, 

 18, 112. Kothner and Aeur, Ber. d. d. chem Gesell., 37, 2536 (1904). Also, 

 Liebig's Ann., 337, 123 and 362 (1904). Baxter, Pro. Am. Acad.,40, 419 (1904)- 



