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has been recently carried to perfection by M. Garcès. When the ores are very rich, as in the mine of Rayas at Guanaxuato, they are only reduced under the stones of the mills to the size of coarse sand (xalsonte), and they separate, by washing, the richest metallick grains (polvil los), which are destined for smelting. This very economical operation is called apartar polvillos.

I have been assured, that in destining for amalgamation silver ores which are very poor in gold, they pour mercury into the vessel or trough, on the bottom of which the stones of the arastras turn; when the auriferous amalgamation goes on in proportion as the ore is reduced to powder: the rotatory motion of the piedras voladeras being favourable to the combination of the metals. I had no opportunity of seeing this operation, which is not practised at Guanaxuato. In some great amalgamation works of New Spain, the arastras are still unknown; they are contented with the braying of the mazos; and the schlich which comes from under them is passed through Sieve sieves (cedazos and tolvas). This comminution is very imperfect; a powder of an unequal and coarse grain amalgamates very ill; and the health of the workmen suffers greatly, in a place where a cloud of metallick dust is perpetually flying about.

The moistened schlich is carried from the

mills or arastras, into the court of amalgamation, (patio or galera) which is generally paved with flags. The flour is ranged in piles (montones) which contain from 15 to 35 quintals. Forty or fifty of these montones form a torta, by which name they call a heap of humid schlich, which they leave exposed to the open air, and which is frequently from 20 to 30 metres in breadth*, by five or six decimetres+ in thickness. They use for amalgamation in a paved court, (en patio) which is the most generally used process in America, the following msterials; muriate of soda, (sal blanca) sulphate of iron and copper, (magistral), lime, and vegetable ashes.

The salt used in New Spain is of very unequal purity, according as it comes from the salt marshes which 'surround the port of Colima on the shores of the South Sea, or the famous laguna del peñon blanco, between San Luis Potosi and Zacatecas. This lake was visited by M. Sonneschmidt. It is situated at the foot of a granite rock, on the slope of the Cordilleras; and it dries up every year in the month of December. It furnishes annually to the revenue nearly 250 thousand fanegas of impure or earthy salt (sal tierra), which is

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all sold to the amalgamation works. On the spot even the price of a fanega is half a piastre. The districts of mines of the intendancy of Mexico, receive salt from the coast of Vera Cruz, and the springs of Chautla; and at Tasco the muriate of soda of Vera Cruz, sells for four piastres the quintal.

The magistral is a mixture of copper pyrites, (kupferkies) and sulphuret of iron, roasted for some hours in a reverberating furnace, and slowly cooled. If it is roasted longer, it produces an acid sulphate of iron and copper, mixed with iron oxidated to the maximum. Sometimes*, though seldom, the azogueros (the name given to the persons charged with the amalgamation) add to the pyrites, during their roasting muriate of soda; so that there is formed sulphate of soda, and muriate of copper and iron. I have also seen vitriolic earths, or copperas, (tierras de tinta o de alcaparosa), which are ochreous earths containing iron oxidated to the maximum, and sulphate of iron, mixed with the magistral. In the district of mines of Real de Moran, they employ in the preparation of the magistral, copper pyrites of San Juan Sitacora, the carga of which is paid for at the rate of ten piastres. The lime is obtained by calcinating very pure limestone, and slaking it with water; and

* Garces, p. 90.

very rarely alkaline ashes are substituted for calcined lime.

It is by the contact of these different substances, namely, moistened metallick powder, mercury, muriate of soda, sulphates of iron and copper, and lime, that the amalgamation of silver, in the process of cold amalgamation, (de patio y por cruto) takes place. They begin at first by mixing salt with the metallick powder, and they stir (repassar) the paste (torta). According to the purity of the salt used, they give each quintal of schlich, a quantity which varies from two and a half to twenty four pounds. If the muriate of soda is of moderate purity, they take from three to four per cent. They call metales salineros, those which are believed to require a great deal of salt, and in which the silver mineral is found in grains of considerable volume. They leave the mineral mixed with salt (metal ensalmorado) for several days, in order that the latter may dissolve and be equally distributed. If the azoguero judges the metals to be warm, (calientes), that is to say in a state of oxidation, and naturally charged either with sulphates of iron and copper which rapidly decompose in the air, or with muriate of silver, he adds lime to cool the mass; and this operation is called curtir los metales con cal. But the use magistral, if the schlich appears too cold (frios); for example, if they

*

proceed from ores which display great metallick lustre; if they contain sulphate of lead (negrillos agalenados), or pyrites difficult to decompose in the humid air; and this operation is called curtir con magistral. They attribute to the sulphate of iron and copper, the property of heating the mass; and they only consider it as well prepared, when, moistened and held in the hand, it causes a sensation of heat. In this case, the sulphuric acid which is concentrated in the acid sulphate, attracts the water and combining with it gives out caloric.

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We have described two processes of chemical preparation of minerals, salting (el ensal morar) and the manner of tanning (curtir) with lime or magistral. After the interval of some days they begin to incorporate (incorporar) the mercury with the metallick powder. The quantity of mercury is determined by the quantity of silver which they think will be drawn from the minerals; and they generally employ in the incorporation, (en el incorporo) six times the quantity of mercury which the paste contains of silver. They allow from three to four pounds of mercury for a marc of silver; and with the mercury or shortly afterwards, they add to the mass, magistral, according to the nature, or (to use the barbarous language of the azogueros) according to the temperature of the minerals (segun los grados

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