while the silver remains as a residue. It was first introduced into Mexico by Bartholomé de Medina in the 16th century, as the smelting processes could not be carried out on account of a scarcity of fuel; the ores are treated in heaps without the application of a high temperature (American system of amalgamation in heaps).

In 1784, Born, an Austrian mining officer, brought this process into Europe, conducting the amalgamation in copper pans. Gellert afterwards employed stationary casks, and at Freiberg Ruprecht first performed this process in rotating casks (European system of amalgamation in casks). In order to facilitate the process, it is partly carried on with the application of a higher temperature.

In both methods the silver contained in the ores is first converted into chloride of silver (in the European system by roasting with common salt, and in the American by treating the ores at the common temperature with chlorides), the chloride of silver is decomposed in the European method by iron, and in the American method direct by mercury; the liberated silver is then seized upon by the mercury, the amalgam is heated, and the remaining silver refined.

The European system of amalgamation is preferable, as it extracts the silver quicker and more perfectly, causing from 8 to 12 times less loss of quicksilver; yet the American plan is still frequently carried out in America in places where quicksilver is cheap, fuel wanting, salt expensive, and machinery not easily obtainable; the climatic conditions of South America also assist the chemical reactions.

To lessen the loss of silver occasioned by roasting, the two processes have been so combined that the transformation into chloride may take place at the common temperature, and casks are employed for amalgamation.

If the silver ores contain much gold it is advisable to treat them in amalgamation mills or pans at a higher temperature without roasting, by adding decomposing agents (potash, acids, &c.)*

*B. u. h. Ztg., 1861, p. 207; 1862, p. 83. WINKLER, die Europäische Amalgamation der Silbererze. Freiberg: 1848.

European Process of Amalgamation in Casks.-This method of extracting silver consumes less time than fusion with lead, and allows a saving of fuel, a quicker and more complete extraction of the silver, a better control of the process, and is cheaper if the price of quicksilver is not very high. On the other hand, the process of amalgamation requires for treatment ores and products free from certain noxious substances, and copper and gold, if present in the ores, are partly lost in the process; this prevents its being as generally applied as the fusion process with lead. Lately, also, other processes have been substituted for it.

According to Röszner,* gold in auriferous and argentiferous ores forms a double salt, Au, Cl,, NaCl + NaCl, which combination is slightly soluble in a solution of common salt, somewhat more so if protochloride of iron be present, but not at all if basic chloride of iron is contained in the solution; it is also undecomposable by quicksilver. Winklert obtained from auriferous silver ore by the amalgamation process auriferous silver containing o'05 per cent of gold, whilst the same ore treated by the fusion process yielded silver containing o'14 per cent of gold.

Janikovits states that by roasting auriferous ores with common salt, chloride of gold is formed, which is reduced by an increased temperature (200° C.) to sub-chloride, and by a temperature of 240° C. to metallic gold.

The process of amalgamation is used for ores, matts, speiss, and black copper.

Amalgamation of Silver Ores.

The ores must be as free as possible from lead, bismuth, copper, gold, nickel, and cobalt, as the first three metals partly combine with the amalgam, and are therefore lost; they also form a tough amalgam which is separated from the residues with difficulty, but renders it richer. These metals chiefly remain in the residues, and can only be extracted by a smelting process.

* Oesterr. Ztschr., 1863, Nos. 25, 40. B. u. h. Ztg., 1863, p. 336.

+ WINKLER, die Amalgamation., i., p. 46. Freiberg: 1848. B. u. h. Ztg., 1861, P. 208.

Ibid., 1861, p. 325.

The presence of lead and bismuth renders the roasting difficult by an inclination to cake; a larger amount of antimony and arsenic increases the volatilisation of silver in the roasting process, and zinc blende has a similar action.* Quartz, heavy spar, and earthy silicates do not interfere at all; calc spar, brown and fluor spar are transformed by the roasting process into sulphates; siliceous and calcareous ores give better results combined, than by themselves; aluminous ores are more difficult to amalgamate.t Pyritic Dürr ores are best adapted for the process if they contain a sufficient amount of pyrites for decomposing the salt in the roasting process, otherwise such fluxes as pyrites, raw matt, or sulphate of iron must be added. If the ores contain too much pyrites, they have to be previously roasted until they contain no more than sufficient sulphide of iron; the residues of ores containing a larger amount of silver will be too rich. The amalgamation process requires the following manipulations :

1. Pounding the Ore.-The finer the ore is pounded the quicker and more perfect will be the transformation of its silver into chloride by the roasting process; the ore is therefore generally ground and passed through a fine sieve.

2. Mixing the Ores.-Siliceous, calcareous, and aluminous ores are mixed in such proportions that the mass contains the proper amount of silver and of sulphides; this is then thoroughly mixed with from 10 to 12 per cent of common salt. In Freiberg they use two different mixtures, a rich one and a poor one, the rich containing from 0'24 to 0.26 per cent of silver, and from 22 to 24 per cent of sulphides of iron, and the poor from o'09 to o'I per cent of silver, and from 24 to 26 per cent of sulphides.

3. Roasting the Ore. The ores are roasted in charges of about 5 cwts. in reverberatory furnaces with either one or two hearths, and provided with condensation chambers. They are spread out upon the hearth, and dried with repeated turnings over at a dull red heat till the decrepitation of the

salt ceases; the caked parts are then crushed with a hammer, and the fire is raised so as to burn the sulphur and keep the ore red hot for about two hours, during which time dense greyish-white vapours of arsenic, antimony, and water are exhaled.

A blue flame next shows the commencement of desulphuration or oxidation, by which the sulphides, the antimony, and arsenic are mostly transformed into salts, part of them also into free oxides. This continues for about two hours, during which time the ignition is kept up, and the mass is thoroughly turned over in order to present new surfaces, and prevent caking. When sulphurous acid ceases to be formed, the final calcination must be commenced with increased firing, the object now being to decompose the salt by means of the metallic sulphates which have been generated, and to convert them into chlorides, with the simultaneous production of sulphate of soda. The stirring is to be continued till the samples drawn from the hearth no longer smell of sulphur, but only of hydrochloric acid. The roasting mass will then have assumed a woolly appearance. This stage of the roasting commonly lasts of an hour.

The fuel (Freiberg) of the first firing is pit coal; of the final one, fir-wood. On an average 115 cubic feet of pit coal and 294 of fir-wood are consumed for every 5 tons of ore.

During the last roasting the ore increases in bulk by onefourth, and consequently becomes a lighter powder, and of a brown colour. When this process is completed the ore is raked out upon the stone pavement, allowed to cool, and then sifted in close boxes, in order to separate the finer powder from the lumps, which are to be broken up, mixed with salt, and subjected to another calcination; the finer powder alone being taken to the mill. (The stones at Freiberg are of granite, and make from 100 to 120 revolutions per minute). The roasted ore, after it has passed through the bolter of the mill, must be as impalpable as the finest flour.

4. The Amalgamation.-Fig. 94 shows the amalgamation machinery used in the works near Freiberg, which furnish. the best model of the European system of amalgamation.

a, is a cask in which the amalgamation is performed; it is 2 feet 10 inches long, 2 feet 8 inches wide, measured inside, and is provided with iron ends. The staves are 3 inches thick, and are bound together with iron hoops. It turns upon a shaft which passes through its axis, and can be made to revolve by the cog-wheel, b. It has a double bung-hole, one within the other, secured by an iron plug fastened with screws. It is filled by means of a hopper (e) in the second story of the building, which is provided with the proper quantity of ore, and by means of the hose (g) the powder falling through the pipe (f) is conveyed directly into the cask. The box (h) holds water, which can be readily carried by the tube (i) into the cask. k, is a tube connected with a reservoir by which the mercury is introduced. At the end of the process the cask is turned so as to have the bung downwards;