60 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



A fourth correction which we sought to determine was for the pos- 

 sible volatility of the argentic chloride during fusion. The constancy 

 of weight on repeated fusion, already mentioned, seems to be sufficient 

 proof for considering this correction as negligible. The conclusion is 

 strengthened by the results of Biltz and Victor Meyer, who found 

 argentic chloride to be but slightly volatile at much higher tempera- 

 ture.* It is not, of course, contended that argentic chloride has no 

 vapor tension at 500 , but only that the loss occasioned by its evapo- 

 ration is too small to receive consideration. 



During fusion, however, there is sometimes a slight spurting, or 

 projection upward of minute drops of fused material. Hence the 

 crucible must always be covered with an accurately weighed lid a 

 precaution which was always taken in the final experiments. 



The phenomenon of spurting suggested that weighable quantities 

 of air may be absorbed during fusion in air, and led to our effort to 

 discover a fifth correction. Carefully conducted experiments showed, 

 however, that there was no loss in weight of 3 grams of ordinarily 

 fused argentic chloride when fused again in a vacuum. The fusions 

 were conducted in a porcelain boat, covered with another inverted to 

 serve as a lid. Slight traces of inclosed gas were noticed by Stas in 

 many substances, but our quantitative experiments showed that they 

 do not amount to a weighable quantity either in common salt or silver 

 chloride. Thus, all the final experiments in this paper refer to sub- 

 stances fused in vacuo, and hence presumably as free as possible from 

 inclosed air. 



There were thus seven possible corrections, besides the correction 

 of the weights to the vacuum standard, which might be applied to the 

 results. Two of these, that for the possible volatility of argentic 

 chloride and that for weight of dissolved air, were so small as to be 

 entirely negligible. The chlorine lost from the traces of argentic chlo- 

 ride clinging to the displaced asbestos shreds was added to the weight 

 of these shreds, and is included therein in the tables below. The 

 three other corrections are recorded in detail in the following tables, 

 which contain the original weight of the precipitate dried at 150 as 

 well as the final corrected values. The almost negligible correction 

 for the solubility of argentic chloride in dilute hydrochloric acid was 

 computed, in the preliminary series, from the volume of the washings. 



*Berichte der d. Chem. Gel., 22, 727 (1889). Kothner and Aeur found a 

 volatilization of only 0.0002 in a case where several liters of gas had heen passed 

 over argentic chloride during several hours. This agrees essentially with our 

 result, for the likelihood of distillation in our case was much less (loc. cit, 

 p. 128). 



