162 THE ATOMIC WEIGHTS. 



If = 16, Al = 27.075. Taking Mallet's work alone, 

 Al =: 27.0089, ± .0028. 



Evidently all the data except Mallet's might be rejected 

 without affecting sensibly the final result. Dumas' work is 

 clearly vitiated by constant errors, but the determinations 

 by Isnard, Tissier, and Terrell may be regarded as having 

 some confirmative value. 



GOLD. 



The onl}^ determinations of the atomic weight of gold 

 which are worthy of consideration are those of Berzelius 

 and of Levol. 



The earliest method adopted by Berzelius* was that of 

 precipitating a solution of gold chloride by means of a 

 weighed quantity of metallic mercury. The weight of gold 

 thus thrown down gave the ratio between the atomic weights 

 of the two metals. In the single experiment which Ber- 

 zelius publishes, 142.9 parts of Hg precipitated 93.55 of Au. 

 Hence, using the value for mercury given in a preceding 

 chapter, 199.712, Au = 196.113. 



In a later investigationf Berzelius resorted to the analj'sis 

 of potassio-auric chloride, 2KCI.AUCI3. Weighed quanti- 

 ties of this salt were ignited in hydrogen ; the resulting gold 

 and potassium chloride were separated by means of water, 

 and both were collected and estimated. The loss of weight 

 upon ignition was, of course, chlorine. As the salt could 

 not be perfectly dried without loss of chlorine, the atomic 

 weight under investigation must be determined by the 

 ratio between the KCl and the Au. If we reduce to a com- 

 mon standard, and compare with 100 parts of KCl, the 

 equivalent amounts of gold will be those which I give in 

 the last of the subjoined columns : 



* Poggend. y\nnal.,8, 177. 

 f Lehrbuch, 5 Aull., 3, 1212. 



