GOLD. 107 



Iii Mallet's fourth series a radically new method was employed. Tri- 

 m ethyl-ammonium aurichloride, N(CH 3 ) 3 HAuCl 4 , was decomposed ly 

 heat, and the residual gold was determined. In order to avoid loss by 

 spattering, the salt was heated in a crucible under a layer of fine siliceous 

 sand of known weight. Several crops of crystals of the salt were studied, 

 as a check against impurities, but all gave concordant values. 



Salt. Residual Au. Percent. A u. 



14-9072 7-3754 49-475 



15.5263 7.6831 49-484 



10.4523 5-1712 49-474 



6.5912 3.2603 49.464 



5-5744 2.7579 49-474 



Mean, 49.474, .0021 



In his sixth and seventh series Mallet seeks to establish, by direct 

 measurement, the ratio between hydrogen and gold. In their experi- 

 mental details his methods are somewhat elaborate, and only the pro- 

 cesses, in the most general way, can be indicated here. First, gold was 

 precipitated electrolytically from a solution of potassium aurocyanide, 

 and its weight was compared with that of the amount of hydrogen simul- 

 taneously liberated in a voltameter by the same current in the same 

 time. The hydrogen was measured, and its weight was then computed 

 from its density. The volumes are given, of course, at and 760 mm. 



Wt. Au. Vol. H, cc. Wt. H. 



4.0472 228.64 . 2 5483 



4.0226 227.03 .0204046 



4.0955 231.55 , .0208103 



These data, with the weight of one litre of hydrogen taken as 0.89872 

 gramme, give the subjoined values in the ratio H : Au : : 1 : x. 



196.960 



197-151 

 196.805 



Mean, 196.972, =b .0675 



In the-last series of experiments a known quantity of metallic zinc was 

 dissolved in dilute sulphuric acid, and the amount of hydrogen evolved 

 was measured. Then a solution of pure auric chloride or'bromide was 

 treated with a definite weight of the same zinc, and the quantity of gold 

 thrown down was determined. The zinc itself was purified by practical 

 distillation in a Sprengel vacuum. From these data the ratio H 3 : Au 

 was computed by direct comparison of the weight of gold and that of the 

 liberated hydrogen. The results were as follows : 



