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have flowed from Europe to Asia, goes no farther back than the year 1557. It was invented in Mexico by a miner of Pachuca of the name of Bartholome de Medina. From the docu. ments preserved in the archives of the despacho general de Indias, and from the researches of Don Juan Diaz de la Calle *, there cannot remain a doubt as to the true author of the inven. tion, which has sometimes been atrributed + to the canon Henrique Garces, who, in 1566, began to work the mercury mines of Huancavelica, and sometimes to Fernandez de Velasco, who in 1571 introduced the Mexican amalgamation into Peru. It is not so certain however, that Medina, who was born in Europe, had not already made experiments in amalgamation before coming to Pachuca. Berrio de Montalvo, an alcalde de corte at Mexico f, and author of a Memoir on the metallurgical treatment of silver ores, affirms, “that Medina had heard in Spain that silver might be extracted by means of mer
* Memorial dirigido al Señor Don Felipe IV. (Madrid 1646) p. 49. Garces, del beneficio de los metales, p. 76–82.
+ Solorzano, Politica de las Indias, lib. vi. C. vi. n. 17. Garcilasso, P. i. p. 225. Acosta, lib. iv. c. ii. Lampadius Handbuch der Hüttenkunde, B. i. p. 401.
| Informe al Excellentiss Señor Conde de Salvatierra, virey de Mexico, sobre el beneficio descubierto por el Capitan Pedro Mendoza Melendez y Pedro Garcia de Tapia (Mexico 1643)
cury and common salt;" but this assertion is supported by no convincing proof. Cold amalgamation was found so profitable in Mexico, that in 1562, five years after the first discovery of the process of Medina, there were already 35 works at Zacatecas * in which minerals were treated with mercury, notwithstanding Zacatecas is three times further from Pachuca, than the old mines of Tasco, Zultipeque, and Tlapujahua.
The Mexican miners do not appear to follow any very fixed principle, in the selection of the ores submitted to smelting or amalgamation; for we see them smelt in one district of mines, the same mineral substances which, in another they believe can only be managed with mer. cury. The ores which contain muriate of silver, for example, are sometimes smelted with carbonate of soda (tequesquite), and sometimes destined to the processes of hot and cold amalgamation ; and it is frequently only the abundance of mercury, and the facility in procuring it, which determine the miner in the choice of his method. In general they find it necessary to smelt the very rich meagre ores, those which contain from ten to twelve marcs of silver per quintal, argentiferous sulphuret of lead, and the ores mixed of blende and vitreous cop
* Descripcion de la ciudad de Zacatecas, por el Conde de Santiago de Laguna, p. 42.
per.' On the other hand, they find it profitable to amalgamate the pacos or colorados *, destitute of metallic lustre; native, vitreous, red, black, and horn-silver ; fahlore rich in silver; and all the meagre ores which are disseminated in very small particles in the gangue.
The ores destined for amalgamation must be triturated, or reduced to a very fine powder, to present the greatest possible contact with the mercury. This trituration under the arastras or mills, of which we have already spoken, is of all the metallurgical operations that which is executed in the greatest perfection, in the most part of the Mexican works. In no part of Europe have I ever seen pulverized ores or pow. dered schlich so fine, and of so equal a grain, as in the great haciendas de plata of Guanaxuato, belonging to Count de la Valenciana, Colonel Rul, and Count Perez Galvez. When the ores are very pyritous, they are burnt (quemar) in the open air in heaps, on beds of wood, as at Sombrerete, or in schlich in . reverberating furnaces (comalillos).
The latter I found at Tehuilotepec: they are 12 metres † in length,
* Alvaro Alonzo Barba, el arte de beneficiar metales 1639, Lib. i. c. iv. Felipe de la Torre Barrio y Lima, minero de San Juan de Lucanas tratado de azogueria (Lima 1738.) Juan de Ordoñez, Cartilla sobre el beneficio de azogue (Merico 1758.) Francisco Xavier de Soria, Ensayo de metalurgia (Merico 1784.)
+ 38 feet. Trans.
without chimneys, but managed by two fires of which the flames traverse the laboratory, This chemical preparation of the ores is however very rare in general ; the size of the fragments of substances to be amalgamated, and the want of combustibles on the table land of New Spain, render the process equally difficult and expensive.
The dry braying is done by mazos, eight of which work together, kept in motion by hydraulical wheels or by mules. The brayed ore (granza) passes through a hide pierced with holes; and it is reduced to a very fine powder under the arastras or tahonas, which are called sencillas or de marco, according as they are furnished with two or four blocks of
porphyry or basalt (piedras voladoras), which revolve in a circle from 9 to 12 metres in cir. cumference.* From 12 to 15 of these arastras or mills, are generally ranged in a row under one shed; and they are moved by water, or mules which are relieved every eight hours. One of these machines brays in the space of 24 hours, from three to four hundred kilogrammest of ores.
The humid schlich (lama) which leaves the arastras, is sometimes washed again in ditches (estanques de deslamar) the construction of which in the district of mines of Zacatecas,
* From 29 to 38 feet. Trans.
† From 662 to 882 lb. avoird. Trans. VOL, III.
has been recently carried to perfection by M. Garcès. When the ores are very rich, as in the mine of Rayas at Guanaxuato, they are only reduced under the stones of the mills to the size of coarse sand (xalsonte), and they separate, by washing, the richest metallick grains (polvillos), which are destined for smelting. This very economical operation is called apartar polvillos.
I have been assured, that in destining for amalgamation silver ores which are very poor in gold, they pour mercury into the vessel or trough, on the bottom of which the stones of the arastras turn; when the auriferous amalgamation goes on in proportion as the ore is reduced to powder: the rotatory motion of the piedras voladeras being favourable to the combination of the metals. I had no opportunity of seeing this operation, which is not practised at Guanaxuato. In some great amalgamation works of New Spain, the arastras are still unknown; they are contented with the braying of the mazos; and the schlich which comes from under them is passed through sieves (cedazos and tolvas). This comminu. tion is very imperfect; a powder of an unequal and coarse grain amalgamates very ill ; and the health of the workmen suffers greatly, in a place where a cloud of metallick dust is
perpetually flying about.
The moistened schlich is carried from the