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In this manner, during the space of two, three and even five months, the paste is balanced between the magistral and the line; for the effects are very different according to the temperature of the atmosphere, the nature of the ores, and the motion given to the schlich. If they imagine that the action is too strong, and that the mass is working too much, they allow it to repose :
or if they wish to accelerate the amalgamation, and increase the heat, they · repeat
oftener the stirring, 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 ores, 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 for washing the remains of the amalgamation.*
* Fragoso de Sequeira, Description de l'amalgamation de Freiberg, 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 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 174 to 10% 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 io 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 quintal 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 ores, 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 copper ; 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 powder, affirming that by this mixture more then 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 copvats. This
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 ore. Hence according to M. Heron de Villefosse, for every 60,000 quintals of ores, they consume or destroy 254 quintals of mercury, (Lampadius, 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.
proposed by M. Born, 1786. The loss of mercury is much less by it than in the beneficio por patio, because the copper of the vessels serves to decompose the muriate of silver, while at the same time the heat favours the operation, either in rendering the action of the affinities more energetic, or in giving motion to the liquid mass which enters into ebullition. This hot amalgamation is used in several of the mines of Mexico, which abound in horn-silver and colorados. Juan de Ordoñez, whose work has been already quoted, even advised amalgamation by means of stoves. In 1676, Juan de Corrosegarra, discovered a process which is very much in use at present, called the beneficio de la pella de plata ; and in which silver already formed is added to the mercury of the amalgam. It is said, that this amalgam (pella) favours the extraction of the silver, and that the loss of mercury is so much less, as the amalgam disseminates itself with greater difficulty into the mass. A fifth method is the beneficio de la colpa, in which, instead of an artificial magistral, which contains much more of the sulphate of copper than the sulphate of iron, they use colpa, which is a natural mixture of acid sulphate of iron and iron oxidated to the maximum. This beneficio de la colpa, extolled by Don Lorenzo de la Torre, offers part of the advantages which we have just
pointed out in speaking of the amalgamation by iron.
The process invented by the miner of Pa. chuca, is one of those chemical operations, which for centuries have been practised with a certain degree of success, notwithstanding the persons who extract silver from ores by means of mercury, have not the smallest acquaintance either of the nature of the substances employed, or the particular mode of their action. The azogueros speak of a mass of ores as of an organized body, of which they augment or diminish the natural heat. Like physicians who in ages of barbarism, divided all aliments and all remedies into two classes, hot and cold, the azogueros see nothing in ores, but substances which must be heated by sulphates if they are too cold, or cooled by alcalies if too warm. The custom which was already introduced in the time of Pliny, of rubbing metals with salt, before applying the amalgam of gold, has undoubtedly given rise to the use of muriate of soda in the process of Mexican amalgamation. This salt, accord . ing to the accounts of the azogueros, serves to clean (limpiar, castrar) and to unskin (desenzurronar) the silver, which is enveloped with sulphur, arsenic, and antimony, as with a skin (telilla or capuz), whose presence prevents the immediate contact of the silver with the mer