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preparation, viz. at the place of trial, where women work, under bocards, and under the tahonas or arastras.

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These tahonas are mametalliferous gangue is triturated under very hard stones, which have a giratory motion, and which weigh more than seven or eight quintals. They are not yet acquainted with washing with the tub (setz wäsche) nor washing on sleeping tables (tables dormantes) (liegende heerde) or percussion (stossheerde). The preparation under the bocards (mazos) or in the tahonas, to which I shall give the name of mills, on account of their resemblance to some oil and snuff mills, differs according as the mineral is destined to be smelted or amalgamated. The mills properly belong only to this last process; however, very rich metallic grains called polvillos, which have passed through the trituration of the tahona are also smelted.

The quantity of silver extracted from the minerals by means of mercury, is in the proportion of 3 to 1 of that produced by smelting. This proportion is taken from the general table formed by the provincial treasuries, from the different districts of mines of New Spain. There are however, some of those districts for example, those of Sombrerete and Zimapan in which the produce from smelting exceeds that of amalgamation.

Silver (plata quintada) extracted from the mines of New Spain, from the 1st January, 1785, to the 31st December, 1789.

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I believe we must augment the quantities stated in the preceding table one fifth to come at the real state of the mines. In times of peace, amalgamation gains a gradual ascendancy over smelting, which is generally badly managed. As wood is becoming yearly more scarce on the ridge of the Cordilleras, which is

the most populous part, the diminution of the produce of smelting is very advantageous to the manufactories which require a great consumption of combustibles. In times of war the want of mercury arrests the progress of amalgamation and compels the miner to endeavour to improve the process of smelting. M. Velasquez, the director general of the mines, supposed even in 1797, before the discovery of the rich mines of Catorce, where there is nearly no smelting, that of all the minerals of New Spain were smelted, and the other amalgamated.

The limits prescribed by us in the execution of this work, do not permit us to enter into any detail of the processes of amalgamation used in Mexico. It may be sufficient to give a general idea of them, to examine the chemical phenomena which are exhibited in the greatest part of these processes, and to show the difficulties which in the New Continent oppose the introduction of the method invented in Germany in 1786, by Born, Ruprecht, and Gellert. Those who may desire to know thoroughly the practice of American amalgamation, will find the most satisfactory information in a work which M. Sonneschmidt proposes to publish. This worthy mineralogist resided in New Spain for the space of twelve years; he had occasion to submit a great number of minerals to amalgamation; and he had it in his power

to discover by his own experience, the advantages and disadvantages of the different methods which have been followed since the sixteenth century in the mines of America.

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The antients knew the property which mercury possessed of combining with gold; and they made use of amalgamation in gilding copper, and collecting the gold contained in their worn out dresses, by reducing them to ashes in clay vessels *. It appears even certain that, before the discovery of America, the German miners used mercury not only in washing auriferous earths, but also in extracting the gold disseminated in veins †, both in its native state, and mixed with pyrites of iron, and with the ore of grey copper. But the amalgamation of silver minerals, and the ingenious process now used in the New World, to which we owe the greater part of the valuable metals existing in Europe, or which have flowed from

* Plin. XXXIII, 6. Vetruv. VII. 8. Beckmann's Gesch. der Erfindungen, B. I. p. 44; B. III. p. 307; B.IV. p. 578.

For example, at Goldcronach, in the Fichtelgebirge, where they still shew the situation of the old amalgamation mills (quickmühlen) for the braying of the auriferous minerals. Valuable documents, have been found in the archives of Plassenbourg, which I had occasion to study during a long residence in the mountains of Steeben and Wunsiedel, that prove the antiquity of the amalgamation works at Goldcronach.

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 documents 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 invention, which has sometimes been attributed † 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 †, and author of a Memoir on the metallurgical treatment of silver minerals, affirms, "that Medina had heard in Spain that silver might be extracted by means of mercury and common salt;" but this assertion is sup

*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 Sen or Conde de Salvatierra, virey de Mexico, sobre el beneficio descubierto por el Capitan Pedro Mendoza Melendez y Pedro Garcia de Tapia (Mexico 1643) p. 19.

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