ATOMIC WEIGHTS 



171 



Mean, 182.827, ± .0101 



Hence Au = 197.24. 



Finally, in eight of these experiments, the silver bromide formed 

 during titration was collected and weighed, giving values for the ratio 

 Au : iVgBr : : 100 : a-, as follows : 



General mean, 95.222, 



.0056 



From Thorpe and Laurie's mean, Au=: 197.25. 



From the second and third of the ratios measured by Thorpe and 

 Laurie an independent value for the ratio Ag : Br may be computed. It 

 becomes 100 : 74.072, which agrees fairly with the direct determinations 

 made by other chemists. Similarly, the ratios Ag : KBr and AgBr : KBr 

 may be calculated, giving additional checks upon the accuracy of the 

 manipulation, though not upon the purity of the original material 

 studied. 



Thorpe and Laurie suggest objections to the work done by Kriiss, on 

 the ground that the salt KAuBr^ cannot be completely dried without 

 loss of bromine. This suggestion led to a controversy between them and 

 Kriiss, which in effect was briefly as follows : 



First, Kriiss ^ urges that the potassium auribromide ordinarily contains 

 traces of free gold, not belonging to the salt, produced by the reducing 

 action of dust particles taken up from the air. He applies a correction 



1 Ber. Deutsch. chem. Gesell., 20, 2365. 18S7. 



