170 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 54 



From all the ratios, taken together, Kriiss deduces a final value of 

 Au= 197.13, if = 16. It is obviously possible to derive still other 

 ratios from the results given, but to do so would be to depart unneces- 

 saril}' from the author's methods as stated by himself. 



Thorpe and Laurie,' whose work appeared shortly after that of Kriiss, 

 also made use of the salt KAuBr^, but, on account of difficulty in drying 

 it without change, they did not weigh it directly. After proving the 

 constancy in it of the ratio Au : KBr, even after repeated crystallizations, 

 they adopted the following method: The unweighed salt was heated 

 with gradual increase of temperature, up to about 1G0°, for several hours, 

 and afterwards more strongly over a small Bunsen flame. This was done 

 in a porcelain crucible, tared by another in weighing, which latter was 

 treated in precisely the same way. The residue, KBr + Au, was weighed, 

 the KBr dissolved out, and the gold then weighed separately. The 

 weight of KBr was taken by difference. The ratio Au : KBr : : 100 : x 

 appears in a third column : 



Mean, 60.331, ± ,0016 

 Hence Au = 197.28. 



This mean combines with Kriiss' thus : 



Kriiss 60.390, ± .0059 



Thorpe and Laurie 60.331, ± .0016 



General mean 60.338, ± .0015 



The potassium bromide of the previous experiments was next titrated 

 with a solution of pure silver by Stas' method, the operation being 

 performed in red light. Thus we get the following data for the ratio 

 Ag: Au:: 100 : x, using the weights of gold already obtained: 



1 .Tourn. Clicm. Sue, 51, 565. 1887. 



