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 t 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

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

2

* 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 me tallick 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.

We have described two processes of chemical preparation of minerals, salting (el ensalmorar) 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

de frialdad). They allow from one to seven pounds of magistral to each pound of mercury; and if the mercury assumes a lead colour (color aplomado,) it is a mark that the paste is working, or that the chemical action has begun. To favour this action, and to augment the contact of the substances, they stir the mass (se da repasso) either by causing about twenty horses or mules to run round for several hours, or by setting workmen to tread the schlich, who for whole days go about barefooted in this metallick mud. Every day the azoguero examines the state of the powder; and he makes the trial (la tentadura) in a small wooden trough (xicara) that is to say, he washes a portion of schlich with water, and judges from the appearance of the mercury and the amalgam, if the mass is too cold or too warm. When the mercury takes an ash colour (en lis cenicienta); when a very fine grey powder is separated from it which sticks to the fingers, they say the paste is too hot; and they cool it by the addition of lime. But if, on the other hand, the mercury preserves a metallick lustre; if it remains white, and covered with a reddish or gilt pellicle (telilla roxiza o de tornasol morado or en lis dorada); if it does not appear to act upon the mass, the amalgamation is then considered to be too cold, and they endeavour to heat it (calentar) by a mixture of magistral.