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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 Frciberg, 1800, p. 36.
The earthy and oxidated parts are carried away by the water, while the amalgam and the mer. cury remain in the bottom of the vat. As the force of the current carries away at the same time some globules of mercury, in the great works, poor Indian women are to be seen employed in gathering this metal from the water used in washing. They separate the amalgam collected at the bottom of the tinas del lavadero from the mercury, by pressing it through sacks; and they mould it into pyramids which they cover with a reversed crucible in the shape of a bell. The silver is separated from the mercury by means of distillation. In the process which I have been describing, they lose in general from eleven and twelve to fourteen ounces of mercury for each marc of silver which they extract, that is to say, from 14 to lip kilogrammes of mercury, for a kilogramme of silver. In the process of amalgamation introduced into Saxony, by M. M. Gellert and Charpentier, the consumption of mercury is \o of a kilogramme per kilogramme of silver, or eight times less than the proportion used in Mexico*.
* In an ordinary year they amalgamate at the work of Halsbrücke, near Freiberg, from 58 to 60 thousand quintals of meagre minerals, which contain from seven to eight lots of silver per quintal (two lots are equal to one ounce). The waste of mercury in amalgamation properly so called (im an-.' We have described the cold amalgamation (por crudo y de patio), without roasting the minerals, and by exposing them in a court to the open air. Medina was only acquainted with the use of salt, and sulphates of iron and cofper ; but in 1586, fifteen years after his process was introduced into Peru, Carlos Corso de Leca, a peruvian miner* discovered the beneficio de hierro. He advised the mixture of small plates of iron with the metallick flour, affirming that by this mixture more than nine tenths of the mercury would be saved. This process, as we shall afterwards see, is founded on the decomposition of the muriate of silver by the iron, and on the attraction of this metal for the sulphur. It is now but very little followed by the Mexican azogueros. In 1590, Alonzo Barba proposed the hot amalgamation in copper vats. This process is called the beneficio de cazo y cocimiento; and it is that which was
quicken), and in washing the remains, is three quarters of an ounce (or a lot and a quarter) per quintal of mineral. In the evaporation of the mercury (ausglühen), they waste a quarter of a lot of mercury, for a quantity of silver corresponding to a quintal of mineral. Hence according to M. Heron de Villefosse, for every 60,000 quintals of minerals, they consume or destroy 25£ quintals of mercury, (Lam. padius, B. ii. p. 178.)
* Carta de Don Juan Carbajal y Sandi presidente de la real audiencia de la Plata, al excellentis, Señor Conde de. Chinchon, virey del Peru, 1736.