l8 ATOMIC WEIGHTS OF SODIUM AND CHLORINE. 



collected separately by placing the anode button in a watch glass or 

 low dish, wholly submerged in the electrolyte. In order to exclude 

 every chance of contamination, no metal but silver may be allowed 

 to come in contact with the electrolyte, although the danger from an 

 immersed platinum wire, either at cathode or anode, is obviously 

 slight. Three samples of silver were thus prepared, called respectively 

 M, N, and P. This silver must have been free from every conceivable 

 impurity, except about 0.02 to 0.05 per cent of the mother liquor from 

 which it was deposited.* This important impurity, consisting wholly 

 of water and argentic nitrate, can be eliminated only by fusing the 

 silver, a matter which will soon be discussed. 



Besides this very pure material used in the work on sodium, 

 several new samples of at least equal purity were made for the even 

 more critical work on chlorine. Three of these new preparations 

 were made from thrice crystallized pure argentic nitrate. A portion 

 of this nitrate was converted into argentic chloride and reduced by 

 pure invert sugar and purified sodic hydroxide. A second portion 

 was reduced by the invert sugar and sodic hydroxide. A third por- 

 tion was reduced by ammonic formiate and amnionic acetate as 

 recommended by Stas. f Some of each of these lots was deposited by 

 electrolysis in a concentrated silver nitrate bath in the usual way 

 (S, T, U, respectively). 



Not content with these preparations although all appeared to 

 be equally pure and anxious to leave no stone unturned whose lift- 

 ing might disclose some new source of error, we made yet two more 

 preparations with new precautions. For one of these, through the 

 great kindness of Mr. Richard Pearce, of the Boston and Colorado 

 Smelting Works at Argo, Colorado, a specimen of metal was secured 

 whose source and history were known as far back as possible. Below 

 is given Mr. Pearce's statement concerning it : 



This specimen is the product of the treatment of ores mainly from Colorado, 

 in which it occurs associated with quartz, barite, calcite, pyrite, sphalerite, with 

 more or less copper in the form of chalcopyrite, together with small quantities 

 of arsenic, antimony, lead, bismuth, and tellurium. The silver minerals are 

 chiefly argentite, polybasite, pyrargyrite, proustite, tetrahedrite, stephanite, and 

 occasionally cerargyrite. A small percentage of the silver comes in copper mattes 

 purchased in other districts, more particularly Montana, where the silver ores 

 are much the same in character, and are smelted with copper ores, forming a 

 matte containing about 200 ounces of silver per ton. 



The roasted ore is mixed with others, principally siliceous, and the mixture 

 is so arranged that, when smelted, it shall yield a slag containing as near as 



*Riohards and Heimrod, Proc. Am. Acad., 37,415 (1902); Richards, Proc. 

 Am. Philos. Soc, 42, 28 (1903); Zeitsch. phys. Chem., 46, 189 (1903). 

 t Stas, Oeuvres, 3, 40. 



