increase in size, appear wherever the particles of lime have touched the mixture; and it is from this peculiar action of the lime, that the azogueros assert it cools the mercury, or prevents the paste from working.

The muriatic acid, disengaged from the muriate of soda by the sulphate of iron, attacks the silver, although the latter is found in its ore in the metallick state. On treating vitreous silver with muriatic acid, we obtain muriate of silver in abundance; and on pouring the same acid on native sulphuret of silver, sulphuretted hydrogen is disengaged. M. Proust observed that the piastres which fell to the bottom of the sea, at the time of the memorable shipwreck of the San Pedro Alcantara, were covered in a short space of time with a crust of muriate of silver of half a millimetre in thickness; and I made the same observation during my stay in Perú at the time of the shipwreck of the frigate Santa Leocadia on the South Sea coast near Cape Saint Helen. M. Pallas affirms † that on the banks of the Jaik in Siberia, old Tartar coins have been found converted into muriate of silver by the contact of an earth which is impregnated with muriate of soda. All these facts tend to prove that in many circumstances, muriatick acid acts upon metallick silver.

* .0196 of an inch. Trans.

† Nordische Beiträge, b. iii. p. 64.

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 cold state, native sulphuret of silver, salt, magistral, lime and mercury, the amalgam formed 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 quantity of silver amalgam. If we pour muriatic acid on the mixture, infinitely more sulphuretted hydrogen is disengaged than we obtain on treating with the same 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 ores mixed with decomposed pyrites, acts in a manner analogous to the filings of iron.

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 were 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 47. 6; for this ratio 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 the moistened powder (schlich); and this division of the metal is so great, that the most careful washing is not sufficient to unite the particles concealed in the residue. 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 air 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 play of chemical affinities.

It results from these researches, that the use of fire will sensibly improve the process of amalgamation. If the minerals to be treated are only vitreous silver, iron filings alone would be perhaps sufficient to lay the silver bare, and

separate it from the sulphur which retards its union with the mercury. But as in all the other silver ores 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 dis, solved; and the muriate of silver which is next to insoluble is decomposed by contact with the mercury.

It has been long proposed to cover the surface on which the torta is prepared 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 Cornejo 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

nois*, a very moderate sum when we consider that the expenses 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 the triturated ores.

The amalgamation, such as we have described it, serves to extract all the silver from the ores 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, ores 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 the residue of amalgamation proceeding from ores, of which the quintal † contained from five to six marcs of silver. In the works of Regla, on the other hand, the schlich frequently undergoes washing before the 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 refuse an enormous mass of silver into the river.

* 12,000l. Sterling. Trans.

+ Sonneschmidt, Miner. Beschreibung der Bergwerks-Reviere, p. 103.