1834.] Gold, by the dry process. 625 



*' The gold to be refined, is beaten out into very thin leaves of 5^ inches square, 

 each weighing about 100 grains. From 100 to 200 of these leaves are piled over one 

 another, being first dipped in a mixture of oil and water, and then smeared over with 

 a composition of three parts of fine old brick-dust, and one part of common salt. 



" A fire of cow-dung is made on tbe ground, upon which the pile of gold leaves 

 is placed, and it is farther sprinkled with some more of the composition. Around 

 the whole, a dome of cow-dung is raised, (see PI. XXXV, fig. 5,) to which fire is 

 applied, and the operator fans it with precaution, that the fire may not become 

 too fierce, and melt the gold. The firing is repeated three times, after which 

 the plates are separated and thoroughly washed. If the purification is to be 

 carried further, another charge of the composition is interstratified with the 

 leaves, and three more fires applied. Sometimes even the whole process is re- 

 peated three times. Bullion of 22 carats pure, is refined to 23 carats, by the first 

 three heats. After six fires, it become 23 carats, 2i grains pure. The expence 

 of the process is very trifling, and every part of the residue is saleable to the 

 under refiners, who extract the silver and copper. 



" The heat employed, measured by a pyrometric alloy cupel, was below the 

 melting point of silver." 



In publishing Dr. Campbell's account, I have with permission omit- 

 ted his reasoning on the rationale of the Nepal process, to make way 

 for a brief notice of some recent observations by the celebrated French 

 chemist Boussingault*, whose experiments have led to a more accu- 

 rate knowledge of the subject than was before to be met with even in 

 the best works. This chemist had an opportunity of witnessing the 

 art, now so completely exploded and obsolete among Europeans, in 

 the mint of New Granada : " Certes c'etait," he writes, " une circon- 

 stance des plus piquantes, que de me trouver au milieu de cette me- 

 tallurgie du ]6eme siecle, non-seulement d'observer ces fourneaux 

 compliques qui rappelaient la philosophic hermetique, mais encore de 

 me rencontrer, scientifiquement parlant, avec des hommes de cette 

 epoque. On croyait voir des chimistes qui venaient de se reveiller 

 apres avoir dormi pendant trois siecles." 



Instead of beating the gold into fine leaves, as in India, the prac- 

 tice at Santa Fe is to granulate it, and dispose the grains in porous 

 earthen vessels, in alternate layers with a cement made of two parts 

 of brick and one part of sea salt. The layers of cement are an inch 

 thick; each pot holds 10 or 15 lbs. of gold ; and the cementation 

 continues from 24 to 36 hours at a cherry-red heat. 



To decompose or reduce the silver, which is retained as a chloride 

 in the bi'ick-dust, the cement is triturated with mercury and one-tenth 

 of fresh common salt, in a humid state. The muriate of mercury is 

 washed off and an amalgam of silver and mercury left behind, which 

 yields a very pure silver, (known in the Calcutta market as plat a pina.J 

 * In the Annales de Chiiuie et de Physique, vol. liv. 1833, page 253. 

 3 L 



