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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 copper; but in 1586, fifteen years after his process was introduced into Peru, Carlos Corso de Leca, a peruvian miner" discovered the beneftcio 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 (ausgliihen), 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, (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, in 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 (argentcorné) 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 Pachuca, 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 minerals 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 minerals 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 azoqueros see nothing in minerals, 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 according 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 mercury. The action of this last metal is ren

dered more energetic by the sulphates with which the mass is heated; and it is even probable that Medina only employed simultaneously, the sulphate of iron and copper, and the muriate of soda, because he discovered in these first attempts, that salt was only favourable to the process in the minerals which contained decomposed pyrites. Without having any clear idea of the action of the sulphates on the muriate of soda, he endeavoured to recompose (refaire) the minerals, that is to say to add magistral to those which the miner considers as not vitriolic. Since the practice of amalgamation of silver minerals was introduced into Europe, and since the learned of every nation met at the metallurgic congress of Schemnitz", the confused theory of Barba, and the Mexican azogueros, has been succeeded by sounder ideas, better adapted to the present state of chemistry. It is supposed that the practice of Freiberg, where a mass of roasted minerals is amalgamated in a very few hours, will be gradually introduced into the Mexican amalgamation, where the minerals are generally not roasted, and where they remain exposed in the open air to the sun and the rain for several months. It is believed that in the moistened mixture of silver minerals, mercury, salt,

* Properly Szkleno or Glashütte, near Schemnitz.

lime, and magistral, this last, which is an acid sulphate of iron and copper, decomposes the muriate of soda; that it is formed of sulphate of soda, and muriate of silver, and that the muriate of silver is decomposed by the mercury, which unites to the disoxidated silver. It is admitted that the lime or the potash, are added to prevent the superabundant sulphuric acid from acting on the mercury. According to this explanation, the silver which is found in its mineral in the metallic state, though united with sulphur, antimony, iron", copper, zinct, arsenici, and leadS, passes into the state of muriate before combining with the mercury. *M. Garces|| a Mexican author, whom we have frequently had occasion to quote, thinks on the other hand, that no muriate of silver is formed in the process of amalgamation. He supposes that muriatic acid only combines with metals which are found united with silver: that water carries off the soluble muriates of iron and copper, and that silver freed from these metallick substances, combines freely with the

* In prismatic black silver. Klaproth's Beiträge, T. i. p. 166. Bergbaukunde B. i. p. 239. -* + In fahlore, weissgiltigerz and graugiltigerz, Klaproth, * T. iv. p. 61. f In fahlore or argentiferous grey copper, § In weisgiotogorz.

| Teorica del Beneficio, p.112–116.

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