226 Principal Silver Mines of Mexico and South America. 



amalgam be hard, more mercury is added, and the mass again knead- 

 ed. If, on pressing the amalgam under the thumb, globules of mer- 

 cury separate, the materials have not been sufficiently incorporated, 

 and the mass is again kneaded and left to ferment. i 



If the amalgam be dark colored, more salt and dung are added, 

 and the mass being then well worked over, is allowed to ferment again. 



If the amalgam, on being pressed under the thumb, form a plastic 

 mass, adhering to the skin, the amalgamation is judged to be com- 

 plete. The amalgamation mass is then washed as in the Mexican or 

 Saxon operations, or sometimes without the aid of machinery, the 

 mud being kneaded in a hide, water being allowed to run into it in a 

 small stream. . The earthy and vegetable substances are carried off 

 in suspension, and to prevent a loss of mercury, the water runs off 

 in a small gutter, connected with small successive reservoirs, in which 

 the metallic particles subside, while the others flow off.* 



In Chili, silver is obtained from its ores only by amalgamation. 

 Even galena, containing silver, is amalgamated, and this appears to 

 be more economical than by smelting and cupellation.f 



Supplementary Notice of the principal Silver Mines of Mexico 

 and South America. 



There are, in Mexico, about five hundred towns, or principal pla- 

 ces, celebrated for the explorations of silver that surround them. 

 These five hundred places of exploration, comprehend, together, 

 about three thousand mines, and there are between four and five 

 thousand veins and masses of silver in exploration. The ore is gen- 

 erally in veins, rarely in beds and masses. 



The vein of Guanaxuato is the greatest and most extensive one 

 known. It is from one hundred and twenty to one hundred and fifty 

 feet thick, and is explored in different places, over a length of about 

 nine miles. 



The silver veins of Mexico are, generally, in primitive and tran- 

 sition rocks, rarely in secondary. The veins of Zimapan are in 

 a greenstone porphyry. Among the transition rocks, limestone 

 abounds most in silver ores. Grauwacke is also very rich in them, 

 and in this rock are found the rich mines of Zacatecas. In the sec- 

 ondary rocks, are found a few rich mines. The mines of Real Ca- 



^ Mier's Travels, ii, p. 393, et seq. t Mier's Travels, ii, p. 406. 



