54 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



was 23.032, the difference of 0.007 ma Y probably be ascribed to plati- 

 num, which had not been precipitated by thermal decomposition. 

 Presumably, therefore, traces of platinum were present also in Stas's 

 preparations. 



In the next place, the effect of the occlusion of sodic chloride by 

 argentic chloride was quantitatively studied. It will be remembered 

 that Stas a/ways dropped dry sodic chloride crystals into his silver nitrate 

 solution instead of adding the salt in the dissolved state. Such a pro- 

 cedure offered the maximum opportunity for the occlusion of sodic 

 chloride. In the following experiments, made with the purest mate- 

 rial (salt F and silver P) and executed with all the precautions 

 outlined above, this error alone was purposely committed. After 

 dropping in the solid salt, the mixture, having been shaken two hours, 

 was allowed to stand for a day, all according to the manner of Stas. In 

 three experiments (Nos. 42, 51, 48,) 5-37 8 53> 3-340i8, and 5-29539 

 grams of salt required, respectively, 9.92510, 6.16392, and 9.77122 

 grams of silver, thus giving three determinations of the atomic 

 weight of sodium, as follows: 23.033, 23.033, and 23,036, or, on the 

 average, 23,034. 



In the last experiment the gradual dissolving of this occluded 

 salt was shown in an indubitable manner. On continued shaking 

 throughout a week, more and more silver had to be added, until finally 

 the mixture came to complete constancy at a point corresponding to 

 9.77264 grams of total silver. This quantity gives 23.028 as the 

 atomic weight of the sodium, showing that within a week nearly if 

 not quite all the occluded sodic chloride had been disengaged. 



If, then, we sum up the effects which we have found for the three 

 chief errors probably imade by Stas in his later work, the following 

 result is obtained : 



Our value of the atomic weight of sodium from the ratio 



of sodic chloride to silver 23 .027 



Effect of too prompt reading of opalescence -f--005 



Presence of platinum in salt + .007 



Occlusion of salt in silver chloride +-007 



Result which we should have obtained by Stas's com- 

 plete method 23.046 



This result is so near that found by Stas's assistants in 1881 

 (23.050) as to make it seem probable that these errors really existed in 

 Stas's work, and that the present investigation avoided them. The 

 acknowledged presence of traces of gas in Stas's silver and silica in 

 in his salt may be neglected in this comparison as being errors of 



