GOLD. 103 



In five of the foregoing experiments the redactions 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. 



An. 4AgBr. Ratio. 



I 3-77753 14-39542 381. oSo 



2 1-67330 6.37952 3S1.254 



5 3.0944S 11.78993 380.999 



6 2.71860 10.35902 381.042 



7 2.53695 9.66117 380.73' 



Mean, 3S1.021, i .057 



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



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

 reduced in a stream of hydrogen, the loss of weight, Br,, 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, Bi-y KBr. 



3 2.50122 3.04422 1.51090 



4 1-59434 1-93937 -96243 



8 4-34997 5-293i6 2.62700 



9 2.51919 3-06534 I-52153 



From these data we obtain two more ratios, viz., Au : Brg : : 100 : x, 

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



An : Br.^. 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, d= .0100 Mean, 60.390, ± .0059 



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- 

 sarily 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 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 + Au, was weighed, 

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



=5 Journ. Chem. Soc, 51, 565. 1887. 



