ore is brought in sacks from the neighboring mines by pack-mules, and it is worked by the cold amalgamation or patio process, which was invented in 1557 by Bartolomé Medina, a Mexican miner. A description of it may be of interest:
The ore is first put in the mill (molino), which is a circular depression in the ground, and crushed by a revolving stone wheel covered with a thick cast-iron tire, and having a horizontal axis. The wheel is moved by two mules attached to a long shaft. There is a coarse iron sieve in the center of the mill, at the base of the vertical post in which the axle of the wheel is fastened. As the ore is crushed, a peon shovels it against the sieve, and the smaller pieces pass through an opening in the ground surrounding the post, and are collected in a vault below. The small particles of ore are now carried in litters to the arrastras, which are flat stones of porphyry, or some other hard rock, about three feet long, which revolve in a large tub.
The tub is half full of water, and the arrastras grind the fragments of silver-ore into a fine powder in about twenty-four hours. Mules are used to give a rotary motion to the arrastras, each animal working six hours. The machinery is run day and night. The next step is the conveyance of the pulverized ore, called lama, in a trough (batea) to the patio or court-yard. The patio is paved with large flat stones, and the soft lama is allowed to accumulate to a depth of about two feet. This muddy mass is then mixed with magistral,[1] or blue vitriol, salt, and quicksilver, by scattering these substances with the hand, and employing mules to walk about in the torta, as it is now termed. A laborer rolls up his breeches and stands in the torta, holding the reins of three mules harnessed together, and drives the animals around him, changing his position every few minutes, in order to impregnate the powdered ore thoroughly with the several chemicals.
The mules tramp through the torta for seven hours daily, and the time required to mix the mass properly varies from two to four weeks, according to the quality of the ore.
The torta is then carried in litters to the lavaderos, or large cisterns, where it is washed and stirred by means of revolving sticks. The silvery mass being heavy, of course, settles at the bottom, and in two or three days the muddy water is drawn off. The amalgam, or pella, which has been formed, is now taken from the lavaderos to a sort of oven or depression in the ground, covered with a huge metallic hood termed a capellina. A fire is built around the capellina, and the mercury is separated by distillation in about four days. The block of silver which remains is transported to the nearest mint, and worked into coin or sold. The law of Mexico com-
- ↑ Native sulphide of iron and copper.
