ATOMIC WEIGHTS 167 



GOLD. 



Among the early estimates of the atomic weight of gold the only ones 

 worthy of consideration are those of Berzelius and Levol. 



The earliest method adopted by Berzelins ^ 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 

 Berzelius publishes, 142.9 parts of Hg precipitated 93.55 of Au. Hence 

 if Hg=300, Au = 196.397. 



In a later investigation ' Berzelius resorted to the analysis of potassio- 

 auric chloride, KCl.AuCla. Weighed quantities 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 inves- 

 tigation must be determined by the ratio between the KCl and the Au. 

 If we reduce to a common 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 : 



4.1445 grm. KAuCl, gave .8185 grm. KCl and 2.159 grm. An. 2G3.775 



2.2495 



5.1300 



3.4130 



4.19975 



Mean, 2C3.730, ± .026 



Hence Au= 196.69. 



Still a third series of experiments by Berzelius^ may be included 

 here. In order to establish the atomic weight of phosphorus he em- 

 ployed that substance to precipitate gold from a solution of gold chloride 

 in excess. Between the weight of phosphorus taken and the weight of 

 gold obtained it was easy to fix a ratio. Since the atomic weight of 

 phosphorus has been better established by other methods, we may prop- 

 erly reverse this ratio and apply it to our discussion of gold. One hun- 

 dred parts of P precipitate the quantities of Au given in the third 

 column : 



1 Poggend. Annalen, S, 177. 

 ^Lehrbuch, 5 Aufl., 3, 1212. 

 SLehrbuch, 5 Aufl., 3, 1188. 



