STAS'S SILVER. 



It is not impossible, however, that yet other impurities might 

 have volatilized with the sodic chloride. In volatilizing his salts, Stas 

 used a boat of pure platinum.* It is possible that pure platinum 

 would itself have volatilized appreciably at the temperature required 

 to drive off 10 grams of salt in half an hour.f For either of the two 

 reasons just given, Stas's correction for impurity in his salt would 

 not have been large enough. 



These impurities must, however, have been almost equally pres- 

 ent in the early and later samples, and could not explain the serious 

 discrepancy between them. At most, 'however, as we shall show, 

 they could hardly have exceeded o.oi per cent, an amount much 

 smaller than the discrepancy in question. Our own experience shows 

 that common salt is a substance very easy to prepare in a pure state. 

 Clearly the cause of the discrepancy must be sought elsewhere. 



The other essential substance, to be prepared in a pure state, was 

 silver. This Stas prepared in a variety of ways, as is well known ; 

 but for all this work the silver was either cast in ingots from under an 

 oxidizing flux, or else ' ' granulated ' ' by dropping into water. His cri- 

 terion of pure silver was the melting of the surface of a button without 

 any apparent irregular expansion as it liquefied, or any flame-color, 

 and the absence of all specks and spots from the completely melted 

 globule. In all experiments it was reddened in a silver crucible before 

 weighing. 



After Dumas had recommended the fusion of silver in a vacuum, 

 Stas made many experiments upon the occlusion of gases by silver. 

 He carefully investigated the samples of silver used in his atomic 

 weight researches, and also new preparations. He found that fusion 

 in a flux of sodic nitrate introduced a quantity of oxygen, and that 

 bars and blocks were slightly purer than ' ' granulated ' ' silver. In no 

 case was the amount of retained gas found by Stas enough to affect 

 seriously even a very accurate analysis ; but, as will be shown later, 

 it is probable that he did not find all the oxygen present. An error 

 in Stas's silver would not account for the discrepancy between his results 

 on sodium and ours ; for an impurity in the silver would cause his 

 atomic weight of sodium to appear too low, and not too high. On 

 the other hand, the impurity in Stas's silver is undoubtedly the cause of 

 the difference between his atomic weight of chlorine and ours. 



*Oeuvres, 1 , 681. 



tSee Hall, J. Am. Chem. Soc, 22, 494 (1900) ; Richards and Archibald, 

 Proc. Am. Acad., 38, 460 (1903); Hulet and Berger, J. Am. Chem. Soc, 26, 

 1512 (1904). There seems to be no doubt that platinum is slightly volatile at 

 1,000 in the presence of air. Probably it is not in pure nitrogen. 



