all sold to the amalgation 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 pyritous copper, (kupferkies) and sulphuretted salt, roasted for some hours in a reverberating oven, and slowly cooled. If it is roasted longer, it produces an acid sulphate of iron and copper, mixed with iron oxidated to the highest degree. 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, pyrites of copper 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 extinguishing it with water;

*Garces, p. 90.

and very rarely alkaline ashes are substituted to calcinated lime.

By the contact of these different substances, namely; moistened metallick flour, 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 flour, and they stir (repassa) 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) to repose 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, with muriate of silver, he adds lime to cool the mass; and this operation is called curtir los metales con cal. But they use magistral, if the schlich appears too cold (frios), for example, if they

proceed from minerals 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 combines with it in getting free from the 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 some days of repose, they begin to incorporate, (incorporar) that is to say to mix the mercury with the metallick flour. 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 rather, to use only 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 repass (se da repasso) or stir the mass, 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 flour; 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.

In this manner, during the space of two, three, and even five months, the paste is balanced between the magistral and the lime; for the effects are very different according to the temperature of the atmosphere, the nature of the minerals, and the motion given to the schlich. Do they imagine that the action is too strong, and that the mass is working too much? They allow it to repose: and in doing so do they wish to accelerate the amalgamation, and increase the heat? They repeat oftener the repassos, sometimes employing men, and sometimes mules. If the amalgamation is formed too quickly, and appears in the form of small globules, called pasillas or copos, they feed the paste (si ceba la torta), by again adding mercury with a little magistral, and sometimes with salt. When from the exterior characters, the azoguero judges that the mercury has united with the whole silver contained in the minerals, and that the paste has yielded (ha rendido), the metallick muds are thrown into vats of wood or stone. Small mills provided with sails placed perpendicularly, turn round in these vats. These machines (tinas de cal y canto) which are particularly well executed at Guanaxuato, have a resemblance to those established at Freiberg, to wash the remains of the amalgamation*.

* Fragoso de Sequeira, Description de l'amalgamation de Freiberg, 1800, p. 36.