40 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



In most experiments the residue of asbestos shreds was found, 

 after ignition, to contain a trace of silver. This was undoubtedly pro- 

 duced from the decomposition of silver chloride during ignition, the 

 latter salt having passed through the Gooch as exceedingly fine parti- 

 cles or having precipitated, in time, upon the asbestos shreds. The 

 amount of this silver, as well as the amount of asbestos shreds, varied 

 according to the efficiency of the Gooch mat and the fineness of the 

 holes of the Gooch filter the smaller those holes, the better. The 

 loss of chlorine upon ignition was determined in sixteen experiments, 

 chiefly in those upon the synthesis of silver chloride. This was done 

 by determining the trace of reduced silver by Volhard's process, using 

 j^ normal solutions. The average of determinations, which varied 

 from o.oo to 0.07 mg., amounted to only 0.02 mg. This correction 

 was applied. Although negligible, its magnitude had to be deter- 

 mined in order that one might be assured of safety in neglecting it. 



With the asbestos at our disposal, the prepared Gooch crucible was 

 not at all hygroscopic. An hour's standing in the balance case had no 

 effect upon its weight. Even upon ignition, the mat, weighing less than 

 0.03 gram, lost only a negligible amount and it was never heated 

 above 150 in the actual analyses. 



As has already been said, no chloride could be found by the neph- 

 elometer in any of the wash waters containing any considerable amount 

 of argentic nitrate. Hence, after filtration through the small filters, 

 these were cast aside and the small solubility correction of 0.03 mg. 

 per liter applied to them. 



The next two or three wash waters containing only small amounts 

 of nitrate were collected separately, because they contained traces of 

 chloride also. The subsequent wash waters, free from nitrate but 

 containing much chloride, were all united. The chloride in both 

 separate portions was carefully determined by means of the nephelo- 

 meter that is, by comparison of opalescence. The two portions, one 

 containing traces of argentic nitrate and one free from salt, must be 

 estimated separately, because if all the wash waters are mixed together 

 the opalescence usually occurs prematurely, a circumstance which 

 interferes with the accuracy of the nephelometric comparison. 



The amount of silver chloride thus found in the wash waters was 

 added to the weight of that collected on the Gooch crucible. 



Any accidentally included foreign substance for example, silica 

 from 'the glass-stoppered flasks, dust from the air, or occluded sodic 

 nitrate which would make the obtained weight of silver chloride too 

 great, would make the computed atomic weight of sodium too low. 

 Since our results were lower than Stas's, particular attention was paid 



