58 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



was dissolved with all the precautions used in previous work and pre- 

 cipitated as chloride by hydrochloric acid at concentrations of about 

 fifth normal. Hydrochloric acid was added in excess and the pre- 

 cipitate was washed three times with dilute hydrochloric acid, in order 

 to diminish as much as possible the solubility of the silver salt. After 

 collection on a Gooch crucible, drying at 150 , and washing, the bulk 

 of precipitate was fused in a porcelain or quartz crucible and the loss 

 in weight by fusion determined. 



It would appear at first as if the result of this process could furnish 

 nothing not directly calculable from a comparison of the two sodium 

 series, in one of which common salt was compared with silver and in 

 the other with argentic chloride. This is not true, however, for in 

 this previous work the precipitate formed in the presence of sodic 

 nitrate and excess of argentic nitrate, while in the present case an 

 occluded alkaline salt could not be carried down, because none was 

 present, and all the silver could be converted into chloride. For this 

 reason the synthesis of argentic chloride in the presence of nothing 

 but volatile substances is an important step in the work. 



As usual, in this case also, improvement was effected as the work 

 progressed, and here as before the less perfect tentative work is included 

 in the preliminary table. The synthesis of argentic chloride is a pro- 

 cess of greater certainty than a metathetical reaction, for the reasons 

 just stated, and hence finer corrections could be discovered and applied. 



These corrections, in addition to the two already heeded, namely, 

 that for the asbestos shreds carried away during filtration and that for 

 the inclosed wash water set free on fusion of the chloride, were five in 

 number. 



The first of these was a correction for the presence of a trace of 

 argentic chloride clinging to the collected asbestos shreds. This silver 

 salt lost chlorine on ignition a quantity which was determined by 



N 



dissolving the residual silver and titrating with sulphocyanate. 



The amount of chlorine thus lost on the average was 0.02 milligram 

 in each synthesis an amount which was added to the weight of the 

 asbestos shreds. This correction might in most cases have been 

 omitted, but it was determined for the sake of certainty. 



The second of these corrections was for the slight solubility of 

 argentic chloride even in dilute hydrochloric acid. This solubility may 

 have been only apparent, the trace found being due to the imperfec- 

 tion of even the double filtration through asbestos and filter paper 

 but in any case it needed determination and correction. The aver- 

 age solubility, from five determinations (page 30), was one part in 



