62 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



Although not giving the true amount of chloride to be obtained 

 from the purest silver, this table was highly instructive. It showed in 

 the first place that even silver of this grade of purity must be o.oi per 

 cent purer than that of Stas.* Again, it showed that at least a part of 

 the difference between the two new values for the atomic weight of 

 sodium is due to an error in the assumed atomic weight of chlorine 

 used in the calculations. It proved that the analytical method was 

 capable of yielding very constant results with a given sample of silver 

 (Exps. 72-76). It confirmed previous resultsf in showing that portions 

 fused in these various ways were not very different, but showed slight 

 variations according to the method of fusion employed. It furnished 

 a means of determining, by later comparison of one or the other of 

 these results with those from the purest silver, the exact grade of 

 purity of the various specimens of silver used in the previous work in 

 this laboratory, in particular that used in the earlier part of the present 

 research. Finally, it furnished sufficient clue to the precautions which 

 must be taken to secure yet purer silver. 



A careful study of this table led to the conclusion that a reducing 

 environment is necessary to eliminate traces of oxygen during fusion, 

 and that lime is better than carbon as a 'support during fusion. The 

 details of this matter have already been described (pp. 22, 23) under 

 the heading " Preparation of Pure Materials," and need not be further 

 detailed here. Suffice it to say that the silver used in the experiments 

 recorded in the table on page 65 was free from the sources of error thus 

 detected. 



The final series comprehends ten experiments, made with four 

 samples of silver prepared entirely independently by three different 



*There can be no doubt that this difference is due to the .fact that Stas fused 

 all the silver used in this part of his work in a porcelain crucible under borax 

 and nitre, thereby introducing both alkali and oxygen (Oeuvres, 1, 328). His 

 own subsequent experiments (Oeuvres, 1, 466) showed that this metal was at 

 least 0.005 P er cent less pure than his distilled granulated silver, which must, 

 in its turn, have contained some oxygen. His still later elaborate search for 

 oxygen in the silver is not satisfactory, because just before determining the 

 oxygen in it he ignited it in a reducing flame, and because he sought to deter- 

 mine the oxygen only by heating to redness in a vacuum, a process which may 

 have set free only the superficial oxygen. Dumas found 0.008 per cent of oxygen 

 in similar silver by fusion in vacuo (Ann. de ohim. phys., 14, 289, 1878), and 

 Mallet found that silver fused like Stas's purest in the oxyhydrogen blast con- 

 tained 0.005 per cent of oxygen. (Phil. Trans., 1 7 1, 1020 [1880]). 

 fRichards, Proc. Am. Acad. 29, 65 (1893). 



