184/.] On the Refinaye of understandard Silver. 561 



terious. These objections might be obviated by the erection of suita- 

 ble screens and hoods, but the refinage never proceeds so successfully 

 as when the native operator is left to his own fashion. Superintendence 

 and the prevention of pilfering become exceedingly difficult also when 

 a large quantity of bullion has to be operated on, from the great num- 

 ber of people employed, the large space occupied by each gang, and the 

 dense smoke and fumes which fill the refinery. 



In the new mint there are three cupellation furnaces by Maudslay, 

 constructed on the most approved plan, and in which the operation 

 could be carried on very effectively and economically were it practica- 

 ble to work the furnaces continuously, night and day ; but as all work 

 must terminate in the mint and the fires be extinguished daily at 4 

 p.m., the furnaces are quite useless. At best no more than 3000 tola 

 weight of silver can be refined in each daily, but with such wasteful 

 expenditure of fuel as to render the operation much more costly than 

 the charge of the native refiners. 



The cursory description above given suffices to explain the object I 

 had in view in attempting, towards the close of 1845, to effect the refi- 

 nage of silver in large, indeed, I may say immense quantities, and to 

 conduct the operation so that the mass of bullion acted upon should 

 be brought into a malleable state, and safely stored, within a period of 

 six *or seven hours. How effectually this has been accomplished is 

 shown in the sequel of this paper. 



My process is based on the old French system of the poussee or salt- 

 petre refinage. This I witnessed in the Laboratory of my friends, Messrs. 

 Johnson and Cock, the eminent refiners in London, and it is minutely 

 described in the works of Dumas and Berthier. The silver to be refin- 

 ed is granulated, the granules mixed with one-tenth their weight of fine 

 saltpetre, and projected gradually into a redhot earthen crucible. The 

 nitre oxydizes the base metals, having but little effect on the silver — 

 when the mass has become red hot the fire is urged till the silver is 

 melted ; the whole is then poured into ingot moulds ; and the scoriae, 

 consisting of potash, oxides of copper, lead and other base metals, with 

 granules of silver and oxide of silver in* considerable quantity, are reserv- 

 ed for subsequent treatment by methods varying according to circum- 

 stances afterwards explained. 



The practical drawback to this system as it existed previous to my 

 experiments, was the supposed necessity of using earthen crucibles. 



4 d -1 



