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facts tend to prove that in many circumstances, muriatic acid acts upon metallic silver.

M. Gay-Lussac and myself succeeded completely in imitating on a small scale the beneficio de hierro, an ingenious process known in Peru since the end of the sixteenth century, and introduced by M. Gellert into Saxony. We perceived that on mixing in a in a cold state, sulphur of natural silver, salt, magistral, lime and mercury, the amalgam forms in greater abundance when we added to the paste filings of iron. In this case the iron not only serves to decompose the muriate of silver, as in the process of amalgamation of Freiberg, but also to separate the sulphur from the mineralised silver. Leaving in contact for 24 hours sulphuretted silver and filings of iron, the silver was put into such a naked state that we obtained in a few minutes a considerable quan tity of silver amalgam. If we pour muriatic acid on the mixture, infinitely more sulphuretted hydrogen is disengaged than we obtain on treating acid sulphuretted silver alone. It is probable that the oxide of iron at the maximum, which is found in the colorados or pacos, and in mineral mixed with decomposed pyrites, acis in a manner analogous to the filings of iron.

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The enormous waste of mercury which we observe in the American process of amalgamation proceeds from several causes which act

simultaneously. If in the process por patio all the silver extracted was owing to a decomposition of muriate of silver by mercury, there would be lost a quantity of mercury which would be to that of the silver in the muriate nearly as 4: 7. 6; for this proportion is that of the respective oxidations of the two metals. Another and perhaps the most considerable part of the mercury is lost, because it remains disseminated in an immense mass of moistened schlich, and because this division of the metal is so great, that the most careful washing is not sufficient to unite the molecules concealed in the remains. A third cause of the loss of the mercury must be sought for in its contact with the salt water, in its exposure to the open and the rays of the sun for the space of three, four and even five months. These masses of mercury and schlich which contain a great number of heterogeneous metallic substances, moistened by saline solutions, are composed of an infinite number of small galvanic piles, of which the slow but prolonged action is favourable to the oxidation of the mercury, and the action of chemical affinities.

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The result of the whole of these researches that the use of fire would sensibly improve the process of amalgamation. If the minerals treated, were only vitreous silver, filings of iron alone would be perhaps sufficient to render the

silver naked, and separate it from the sulphur which retards the union of the silver with the mercury. But as in all the other silver minerals there are besides

sulphur different metals combined with the silver, the simultaneous employment of muriate of soda and sulphates of copper and iron, becomes necessary to favour the disengagement of the muriatic acid which combines with the copper, iron, antimony, lead, and silver. The muriates of iron, copper, zinc, and arsenic, and even that of lead remain dissolved; and the muriate of silver which is completely insoluble is decomposed by contact with the mercury.

It has been long proposed to cover the surface on which the pastes repose with plates of iron and copper instead of flags; and it has been endeavoured to stir (repassar) the mass by working it with ploughs of which the share and coulter should be made of the metals which we have been mentioning; but the mules suffered too much from this work, the schlich forming a thick and by no means ductile paste. The custom of treading the schlich by mules instead of men was only introduced into Mexico in the year 1783. Don Juan Comejo brought from Peru the idea of this process; and the government granted him a privilege for it, which he did not long enjoy, and which only brought him in the sum of 300,000 livres tour

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nois*, a very moderate sum when we consider that the expences of amalgamation have been more than a fourth diminished since it has been no longer necessary to employ the great number of workmen who trod barefooted on heaps of metallic flour.

The amalgamation such as we have described it, serves to extract all the silver from the minerals which have been treated by mercury, provided the azoguero be experienced, and thoroughly know the aspect or exterior characters of the mercury, by which to judge if the paste is in want of lime or sulphate of iron. At Guanaxuato where this operation is best managed, minerals are successfully amalgamated which contain only three fourths of an ounce of silver per quintal. M. Sonneschmidt found only, of an ounce of silver in remains of amalgamation proceeding from minerals, of which the quintalt contained from five to six mares of silver, In the works of Regla the schlich frequently undergo washing before mercury has extracted all the silver in the paste; and it is believed at Mexico that the father of the present proprietor of the famous mine of Biscaina threw with the remains an enormous mass of silver 'into the river.

* £12,000 Sterling. Trans.

+ Sonneschmidt, Miner. Beschreibung der BergwerksReviere, p. 103.

The process discovered by Medina possesses the great advantage of simplicity: it requires no construction of edifices, no combustibles, no machines, and almost no impelling force. With mercury and a few mules to move the arastras, we may by means of amalgamation por patio extract the silver from all the meagre minerals near the pit from which they are taken in the midst of a desert, provided, the surface be sufficiently smooth to admit of the establishment of the tortas; but this same process has also the great disadvantage of being slow and causing an enormous waste of mercury. As the mercury is divided in an extreme degree, and thousands of quintals of minerals are wrought at a time, it is impossible to collect the oxide and muriate of mercury which are carried away by the water in washing. In the method of amalgamation followed in Europe which we owe to the learned researches of M. M. Born, Ruprecht, Gellert, and Charpentier, the silver is extracted in the space of 24 hours. They employ from sixty to one hundred and fifty times less time than in the Spanish colonies, and consume as we have already said eight times less mercury. But how is there a possibility of introducing into Mexico or Peru, the process of Freiberg, which is founded on the roasting of the minerals, and the giratory motion of the tubs? At Freiberg sixty thousand quintals

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