FUSION OF SODIC CHLORIDE IN VACUUM. 55 



mutually opposing tendency and almost equal effect. The rectifying 

 of previous work by means of a later correction is always a doubtful 

 process, and the above table is given only to show that Stas's small 

 mistakes have all been traced. 



It not so easy to give the numerical magnitude of the correction 

 to be applied to Stas's eaiiicr work, which, as has been said, is incon- 

 sistent with the later work, because it gives the same result, although 

 a wholly false end-point was used. It is probable, however, that in the 

 early work, carried out by Stas himself, the precipitated argentic 

 chloride was much more thoroughly shaken with its mother liquor 

 than the later work executed by MM. Nyst and Cabilliauw under Stas's 

 direction. Continued shaking would diminish the solubility of the 

 argentic chloride, as well as disengage the occluded salt. Thus the 

 decrease of the latter error might have balanced the effect of a greater 

 error in the end-point, although this in its turn would be less marked 

 than it would have been had the mixture been less thoroughly shaken. 



All these considerations tend to support the present determination 

 as against the verdict of the older ones, but no explanation is yet 

 afforded as to the reason for the difference between the values 23.017 

 and 23.027 found by different processes in the present work. Long 

 consideration of the matter led finally to the conclusion that the 

 accepted value of the atomic weight of chlorine, 35.455, upon which 

 the calculation depends, must be in error. Accordingly this problem 

 also was attacked experimentally. But before these lengthy experi- 

 ments are recounted brief mention must be made of the successful 

 attack upon another doubtful point, which concerns the sodic chloride. 



THE FUSION OF SODIC CHLORIDE IN VACUUM. 



This matter has been given an especial heading because it is one 

 which has never before received adequate treatment in an investigation 

 of this kind. It is well known that many substances, when fused in 

 the air, dissolve either oxygen or nitrogen, or both, thereby increas- 

 ing sensibly their weight. While it was hardly to be expected that 

 this would be the case with sodic chloride, the point should not pass 

 unchallenged in a research striving to attain the highest possible 

 accuracy. 



Hence two analyses were made of sodic chloride fused for some 

 time in a platinum boat inclosed in a completely evacuated porcelain 

 tube, and subsequently bottled in dry air in the often described " bot- 

 tling apparatus." So far as we know these are the only quantitative 

 experiments ever made in which all the weighed substances were fused 



