Page:Pictures of life in Mexico Vol 1.djvu/252

224 earth, and lined with the hardest rock that can possibly be obtained. On the inside of these cisterns are suspended, by means of beams turning on a pivot, tiers of grinding stones, likewise of the very hardest quality. The pulverized ore is thrown into these receptacles, the beams are turned by mules, and an impalpable powder is the result. Water and a little salt are added during the operation; and the mass thus presents the appearance of a thick, paste-like substance. It is then time to separate the particles of silver from the rocky fragments to which they have adhered for ages.

To attain this desirable end, the mixture is spread thinly over some convenient open ground, and great quantities of mercury, together with salt, and some sulphates, muriates, and other chemical substances, are gradually added to it, forming an amalgam. It is allowed to remain in this state for several days, when it is worked about and pressed by horses; more water and chemical preparations are added to it; and when the different components are by these means sufficiently mingled, it is ready for the washing or purifying machine.

The last-mentioned contrivance is not very