RICHARDS. — ATOMIC WEIGHT OF BARIUM. 65 



The three samples of beautiful crystals of silver thus obtained by- 

 electrolysis naturally contained a minute amount of imprisoned mother 

 liquor, which is best expelled by fusion. Many precautions were 

 taken to prevent the absorption of an impurity during this process. 



In the first trials pure hard-wood charcoal was used to support the 

 metal during its fusion in the flame of the ordinary blast lamp (Ex- 

 periments 30, 31, and 32). Afterwards a cupel of sugar charcoal was 

 substituted for the wood charcoal. Such cupels are readily made by 

 mixino- finely powdered pure sugar charcoal with about a third of its 

 weight of pure powdered sugar, and igniting in closed moulds. The 

 silver used in Analyses 35, 36, 38, 42, and 43 was fused in this way. 



A possible absorption of sulphur from illuminating gas being feared, 

 a number of buttons of silver were fused upon the sugar charcoal 

 cupels by the use of a blast lamp in which only pure alcohol, vapor- 

 ized in a steam bath, was burnt. Such silver was used in Experi- 

 ments 33, 34, 37, 39, and 40. All of these specimens of silver had 

 been cooled with care in the centre of a strongly reducing flame, to 

 prevent the absorption of oxygen ; and any button which showed a 

 trace of such absorption was of course discarded. Proof has already 

 been given * that no oxygen is held after such treatment ; but in order 

 to '■ make assurance doubly sure " three grams and a half of the 

 purest crystals were placed upon a boat made of sugar charcoal, 

 enclosed in a stout porcelain tube, and fused in a vacuum (Experi- 

 ment 41). 



The results obtained from these different varieties of silver may 

 well be recorded here, although the details must be reserved until 

 nearly the end of the present paper. The first specimen of silver 

 fused upon wood charcoal was used in experiments which were vitiated 

 by other serious errors, so that the results from it need not be given. 

 The figures given below represent the amount of silver required 

 exactly to precipitate 100.000 parts of baric chloride.f 



* These Proceedings, XXV. 198. 



t The results obtained from Stas's second method, described later, are 

 omitted from this series. 



vol. xxix. (n. s. xxi.) 5 



