48 Transactions. 



A j)iece o£ stout silver wire was ignited with this salt for one quarter of 

 an hour, the fused mass allowed to cool, and then examined, when an abun- 

 dance of chromate of silver Avas discovered to have been formed, while the 

 wire had been greatly corroded and reduced to half its bulk. 



A second piece of silver wire was completely dissolved in a subsequent 

 fusion with the chromate for an equal time. 



Gold (and platinum) treated in like manner refused to dissolve, at least 

 to any perceptible extent. 



It is therefore certain that in bichromate of potash we have a means 

 of separating silver from native gold, at least to some extent, but to what 

 extent could not well be determined in the Laboratory. In any case, 

 the method is well worth a trial by assayists and bank managers. 



The manner of application is simply to place the salt upon the surface 

 of the molten metal. I should not consider it at all necessary to attempt their 

 mechanical admixture, as the silver being taken up from the top, currents 

 would be produced in the metallic mass, and kept up with gradually 

 decreasing force until the whole of the silver was removed. Possibly an 

 intermittent agitation of the saline portion might be found advantageous. 



To prevent loss of silver by volatihzation, it is indispensable that the 

 bichromate should be free from chlorides. 



Besides the separation of silver from auriferous alloys, this method is 

 equally effective in removing copper and iron when present. To insure, 

 however, the continuous fluidity of the saline stratum, the application of 

 borax might be continued, but nitrates or caustic alkalies must be rigorously 

 excluded. 



The silver is easily recoverable, as the chromate, being soluble in water, 

 may be dissolved therein, the silver precipitated by hydrochloric acid, and 

 the resulting chloride of silver finally decomposed by soda. 



The quantity of bichromate theoretically required to oxidize the silver 

 and form with it this salt, is 5 eqiiivalents to every 3 equivalents of silver, 

 or, weight for weight, one pound of silver would require two and thirty -four- 

 hundredths of a pound of the bichromate ; but in practice the quantity re^ 

 quired would no doubt be more, as some of the oxygen would be liberated 

 out of contact with the alloy. For this reason it would be best to add the 

 salt in successive portions, and for the same reason it is probable that the 

 process would be found more adapted to the separation of silver when pre-i 

 sent in proportionally small quantities. 



Allowing, however, an equal Aveight of the salt for loss of this kind, and 

 taking its retail price at Is. 6d. per pound, — as per Jachson and Townson's 

 Price List, — every pound of the silver Avould incur a cost, on this head, of 

 7s. for its removal. 



