ATOMIC WEIGHTS 173 



In the third series of experiments the salt K^uBr^ was taken, purified 

 bv five recrystallizations. The solution of this was weighed out into 

 nearly equal parts, the gold being measured as in the two preceding 

 series in one portion, and the bromine thrown down by a standard silver 

 solution as before. This gives the ratio 4Ag: Au : : 100 : x. 



Mean, 45.689, ± .0040 



Hence Ag: Au: : 100 : 182. 756, ±.0160, and Au = 197.16. 



The fifth series of determinations, which for present purposes naturally 

 precedes the fourth, was electrolytic in character, gold and silver being 

 simultaneously precipitated by the same current. The gold was in solu- 

 tion as potassium aurocyanide, and the silver in the form of potassium 

 silver cyanide. The equivalent weights of the two metals, thrown down 

 in the same time, were as follows, giving directly the ratio Ag : Au : : 



100: a:. 



Au. Ag. Ratio. 



5.2721 2.8849 182.748 



6.3088 3.4487 182.933 



4.2770 2.3393 182.832 



3.5123 1.9223 182.713 



3.6804 2.0132 182.814 



Mean, 182.808, ± .0256 



Hence Au = 197.22. 



This mean may he combined with the preceding means, and also with 

 the determination of the same ratio by Thorpe and Laurie, thus : 



Thorpe and Laurie 182.827, ± .0101 



Mallet, chloride series 182.730, ± .0102 



Mallet, bromide series 182.781, ± .0114 



Mallet, KAuBr, series 182.756, ± .0160 



Mallet, electrolytic 182.808, ± .0256 



General mean 182.778, ± .0055 



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

 methyl-ammonium aurichloride, NCCH.OgHAuCl^, was decomposed by 

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

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