GOLD. 103 



In five of the foregoing experiments the reductions were effected with 

 sulphurous acid ; and in these, after filtering off the gold, the bromine 

 was thrown down and weighed as silver bromide. This, in comparison 

 with the gold, gives the ratio Au : 4AgBr : : 100 : x. 



Au. <j.AgBr> Ratio. 



i 3-77753 H.39542 381.080 



2 1.67330 6.37952 381.254 



5 3- 9448 ".78993 380.999 



6 2.71860 10.35902 381.042 



7 2.53695 9.66117 380.731 



Mean, 381.021, . .057 



Hence Au : AgBr : : 100 : 95.255, .0142. 



In the remaining experiments, Nos. 3, 4, 8, and 9, the KAuBr 4 was 

 reduced in a stream of hydrogen, the loss of weight, Br 3 , being noted. 

 In the residue the gold was determined, as noted above, and the KBr 

 was also collected and weighed. The weights were as follows : 



Au. Loss, Br z . KBr. 



3 2.50122 3-04422 1.51090 



4 1-59434 1-93937 -96243 



8 4-34997 5- 2 93 l6 2.62700 



9 2.51919 3-06534 L52I53 



From these data we obtain two more ratios, viz., Au : Br 3 : : 100 : SB, 

 and Au : KBr : : 100 : x, thus : 



Au : Br z . Au : KBr. 



3 121.710 60.405 



4 121.641 60.365 



8 121.683 60.391 



9 121.680 60.398 



Mean, 121.678, .0100 Mean, 60.390, .0059 



From all the ratios, taken together, Krtiss 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- 

 sarily from the author's methods as stated by himself. 



Thorpe and Laurie, * whose work appeared shortly after that of Kruss, 

 also made use of the salt KAuBr 4 , but, on account of difficulty in drying 

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

 stancy 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 160, 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 -f Au, was weighed, 

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



* Journ. Chein. Soc., 51, 565. 1887. 



