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Rh authority on this subject. In his Treatise on the Art of refining Metals, Don Alonzo Barba, rector of San Bernardo in Potosi, makes the following observations: "It may be asserted without exaggeration, that many thousands of piastres have been, lost, as well in the extraction of the metallic substance from the ores, the qualities and differences of which have not been well understood; as in the disproportionate expenditure of quicksilver, of which upwards of two hundred and thirty-four thousand seven hundred quintals have been consumed, in the space of sixty-three years, in the imperial city of Potosi. Those who have been engaged in this pursuit, have, in the management of the ores, proceeded at random, and without any fundamental rules, or certain information relative to the silver they contained, and might be made to yield."

Notwithstanding the ignorance of mineralogy was attended by such prejudicial consequences, it would be difficult to believe, that it reached the unfortunate extreme which is described in an ancient and authentic document by Don Francisco Texada, intendant of the mine of Guadalcanal, dated in 1607. Speaking of the productiveness of many of the ores dug from the silver mines of Europe, each quintal of which yielded fifteen, thirty, and even sixty marks of the pure metallic substance, he adds as follows: "In the celebrated mountain of Potosi, which is now working, there is not a greater produce than one ounce and a half of pure and limpid silver, from each quintal of metallic earth, or stone, which is extracted; or, in other words, one thousand six hundred ounces