110 THE ATOMIC WEIGHTS. 



A fourth combustion of the oxalate is omitted from the 

 above series, having been rejected by Favre himself. In this 

 the oxide formed was contaminated by traces of sulphide. 



The four values for zinc now before us are so discordant 

 that a combination of them after the usual method can have 

 only a trifling significance. The following is the result thus 

 obtained : 



From Jacquelain's figures Zn = 66.072, ± .028 



From P'avre's water series " := 65.803, h= .020 



From Favre's oxalate series__ " == 65.8395, ± .022 

 From Erdmann's figures " =; 64.9045, d= .019 



General mean " -- 65.557, rt .011 



It will be seen that three of these values agree tolerably 

 well, placing the atomic weight of zinc in the neighborhood 

 of 66, while the other is, in round numbers, about a unit 

 lower. This lower figure, however, has the smallest proba- 

 ble error, and it will be found also, upon careful considera- 

 tion, that it is less likely than the others to be vitiated by 

 experimental inaccuracies. Both chemically and mathe- 

 matically it is the best. 



Upon comparing Erdmann's results with those of Jacque- 

 lain two points are worth noticing: first, Erdmann worked 

 with purer material than Jacquelain, although the latter 

 applied corrections for the impurities which he knew were 

 present; secondly, Erdmann calcined his zinc nitrate in a 

 porcelain crucible, while Jacquelain used platinum. In the 

 latter case it has been shown that portions of zinc may be- 

 come reduced and alloy themselves with the platinum of 

 the crucible. Hence a lower weight of oxide from a given 

 quantity of zinc, a higher percentage of metal, and an in- 

 creased atomic weight. This source of constant error has 

 undoubtedly aff'ected Jacquelain's experiments, and vitiated 

 his results. In Erdmann's work no such errors seem to be 

 present. 



Over Favre's experiments Erdmann's have the important 

 merit of simplicity. In the latter it is difiicult to detect 

 sources of error ; in the former it is eas}'. In Favre's water 



