66 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



gives no clue as to possible constant errors involved. A better idea of 

 the chemical trustworthiness of the result is got by comparing the 

 data furnished by the two different methods of synthesis. The averages 

 of the seven determinations by the method of filtration is 132.8666, 

 while that of the three by the method which involves no transference 

 of material (83, 84, 85) is 132.8673. These are both within the range 

 from the mean 132.8668 indicated by the " probable errors" of the 

 respective averages, and hence may be considered as identical. 



If the comparison be made according to the environment of the 

 silver during fusion, a similar result is obtained. The silver fused in 

 hydrogen gives an average of 132.8668, while that fused in a vacuum 

 gives 132.8668. Again this is essential identity. 



In view of these facts, the fact that all probable errors tend to 

 lower the result, and the multitude of precautions which eliminated 

 error from these figures, it is not unsafe to conclude that 100.000 parts 

 of the purest silver really yields as much as 132.867 parts of argentic 

 chloride. This conclusion confirms the comparison of the silver and 

 argentic chloride indicated by the work on sodium, and shows that no 

 great occlusion of sodic nitrate could have taken place there. It 

 furnishes, moreover, a means of determining by comparison the purity 

 of any other specimen which has been used in the quantitative synthesis 

 of argentic chloride by either of the foregoing methods. For example, 

 it shows that the silver used in the work on sodium silver which 

 yielded 132.862* parts of chloride must have contained j^ = 27000 = 

 0.0037 P er cen t of impurity. 



*See Syntheses 65, 66, and 70 given in the table on page 61. The silver used 

 in these syntheses was exactly similar to some of that used in the work on 

 sodium. In the same way, if Stas's method of synthesis is considered as com- 

 parable with ours, his silver must have contained (132867 132848) -s- 132867 = 

 0.015 per cent of impurity. It is doubtful, however, if the methods of synthesis 

 are strictly comparable. 



