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minished in proportion to the increase of the works in depth. In this point of view, and in many others besides, the Cerro de Potosi bears a great analogy to the mines of Gualgayoc. At the surface of the earth, the veins of Rica, Centeno and Mendieta, which traverse primitive slate, were full, throughout the whole of their width, of a mixture of sulphuretted, red, and native silver. These metallic masses rose in the form of crests (crestones), the rocks of the wall and roof having been destroyed either by the action of water, or by some other causé which has changed the surface of the globe. The Veta del Estaño, on the other hand, contained at its surface, only sulphuret of tin, and the horn silver ores only began to appear at great depths. This mixture of two formations in one vein, exists also on the Old Continent, for example, in several mines of Freiberg in Saxony. t In 1545 ores containing from 80 to 90 marcs per quintal were very common ; but we cannot admit with Ulloa that the whole bulk of ores extracted from the mine, amounted to this degree of wealth. Acosta says expressly, that in 1574 the mean produce was from 8 to 9 marcs, and that the ores which yielded 50
marcs per quintal were considered extremely rich. Moreover, according to the report of Don Francisco Texada on the mines of Guadalcanal in Spain, in 1607, the mean produce of the ores of Potosi was not above an ounce and a half. Since the commencement of the 18th century, they reckon only from 3 to 4 marcs per caxon of 5000 pounds, or from 7am to mato per quintal. The ores of Potosi are consequently extremely poor, and it is on account of their abundance alone, that the works are still in such a flourishing state. It is surprising to see that from 1574 to 1789, the mean richness of the ores has diminished in the proportion of 170 to 1, while the quantity of silver extracted from the mines of Potosi, has only diminished in the proportion of 4 to 1.
From 1515 till 1571 the silver ores of Potosi were all smelted. The knowledge of the con. quistadores being confined to military affairs, they were unacquainted with the carrying on of metallurgical processes. When their attempts to smelt the ores by means of bellows proved unsuccessful, they adopted the whimsical method employed by the Indians in the neighbouring mines of Potosi, which had been wrought on account of the Inca, long before the conquest; they established on the mountains which surround the town of Potosi, wherever the wind
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blew with impetuosity, portable furnaces, called huayres or guayras in the Quichua language. These furnaces were cylindrical tubes of clay, very broad, and pierced with a great number of holes. The Indians threw in layers on layers of silver ore, galena, and charcoal ; and the current of air which entered at the holes into the interior of the huayre quickened the flame, and
gave it a great intensity. When they perceived that the wind blew too strong, and that too much fuel was consumed, they carried their furnaces to a lower situation. The first travel. lers who visited the Cordilleras, all speak with enthusiasm of the impression made on them by the first
appearance of more than 6000 fires, which illuminated the summits of the mountains round the town of Potosi. The Indians extracted the galena necessary for their smelting, from a smaller mountain, in the vicinity of the Cerro de Hatun-Potocsi called the child, or Huayna Potocsi. * The argentiferous masses which came out of the huayres established in the mountains,
* Properly the Father-mountain and the Son-mountain. The different summits of the Volcan de Pichincha, bear analogous denominations ; and it is because the French academicians have not distinguished in their works the old RucuPichincha from the young, or Guagua-Pichincha, that it is so difficult to find the place of the academical station of Bouguer, La Çondamine, and Ulloa. (See my Recueil d'Observations Astronomiques, vol. i. p. 308.)
were resmelted in the cottages of the Indians, by means of the old process of blowing the fire by ten or twelve persons at once, through tubes of copper, of one or two metres in length, and pierced at the lower extremity with a very small hole. It is easy to conceive what an enormous quantity of silver must have remained in the scoriæ without combining with the lead.
Pedro Fernandez de Velasco, who, it is ex. pressly said by the jesuit Acosta *, “ had seen in Mexico how the silver was extracted from the ore by means of mercury,” proposed to Francisco de Toledo, viceroy of Peru, to introduce the process of amalgamation into Potosi. He succeeded in his attempts in 1571 ; and of the eight or ten thousand quintals of mercury produced by the mine of Huancavelica towards the end of the 16th century, more than from six to seven thousand were consumed in the works of Potosi. The ores which during the first years had been considered too poor to be smelted in the huayres, were now wrought to advantage.
The abundance of rock salt wrought on the table land of the Cordilleras near Cuchuara, Carangas, and Yocalla, facilitates very much
the amalgamation of Potosi. According to the calculation of Alonzo Barba*, there was consumed between 1545 and 1637 the enormous quantity of 234,700 quintals of mercury. From 1759 to 1763, the consumption was between sixteen and seventeen thousand quintals annually. t Towards the end of the 16th century, 15,000 Indians were compelled to work in the mines and amalgamation works of Potosi, and more than 1500 quintals of salt of Yocalla were daily brought to the town. At present there are not more than 2,000 miners, who are paid at the rate of 50 sous # per day. Fifteen thousand llamas, and an equal number of asses are employed in carrying the ore from the mountain of Hatun-Potocsi to the amalgamation works. In 1790 there were coined at the mint of Potosi 4,222,000 piastres ll, viz. 299,246
piastres, or 2204 marçs in gold, and 3,293,173 - piastres, or 462,609 marcs in silver.
When we reflect on the history of the precious metals, and the interest taken in them by those who engage in investigations of political economy, it will not be deemed surprising that we have so minutely explained those facts, which
* Barba, p. 12 and 65.