GOLD. 107 



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

 methyl-ammonium aurichloride, N(CH3)3HAuCl^, was decomposed by 

 heat, and the residual gold was determined. In order to avoid loss b}^ 

 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 All. Per cent. Au. 



14-9072 7-3754 49-475 



15.5263 7-6831 49484 



10.4523 5-1712 49-474 



6.5912 3-2603 49-464 



5-5744 2.7579 49-474 



Mean, 49.474, i .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 onl}^ 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- 

 taneousl}' liberated in a voltameter by the same current in the same 

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

 from its densit3^ The volumes are given, of course, at 0° and 760 mm. 



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 : a;. 



196.960 



197-151 

 196.805 



Mean, 196.972, ± .0675 



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

 dissolvegl 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 II3 : Au 

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

 liberated hydrogen. The results were as follows : 



