Dark Red Silver Ore, 3AgS+ SbS, containing 59 per cent of silver; part of the SbS, is sometimes replaced by AsS,. Mixtures of both occurring at Freiberg, contained from 60*75 to 62.50 per cent of silver.

Dark White Silver Ore, 4(Cu2S, FeS, ZnS, AgS) + SbS, with 18 to 31.8 per cent of silver and 15 to 26 per cent of copper.

Light White Silver Ore, 4(FeS, ZnS, PbS, AgS) + SbS ̧, occurring at Freiberg with 38 per cent of lead, 5'7 per cent of silver, and traces of copper.

Silver Copper Glance, Cu,S+AgS, containing 53 per cent of silver and 31 per cent of copper.

Chloride of Silver, AgCl, containing 75°2 per cent of silver. Megabromite, an isomorphous mixture of chloride and bromide of silver, 4AgCl + 5AgBr, containing 64°2 per cent of silver.

Microbromite, AgBr + 3AgCl, containing 69.8 per cent of

silver.

Embolite, 2AgBr + 3AgCl, containing 66'9 per cent of silver.

Bromite, Bromargyrite, bromide of silver, AgBr, containing 58 per cent of silver.

Iodide of Silver, AgI, containing 46 per cent of silver.

Silver in combination with chlorine, bromine, and iodine forms a class of ores which was once considered rare, but has since been found to constitute a valuable portion of many veins. They are generally found disseminated in a different part of the deposit from that in which the sulphides are found, and are associated with clay, quartz, calc spar, and baryta.

At Huëlgoet, in Brittany, they constitute the ore known. as terres rouges; they contain an average of 0.05 per cent of silver, and are subjected to amalgamation. In Spain, the chloride appears to have existed in considerable quantities at the mines of Guadalcanal. Large quantities of this class of ores are worked in Chili, Peru, and Mexico; the veins in which they are found usually contain in their lower portions sulphides, arsenides, and compounds of antimony; they are also also found in the mines of Norway, Saxony,

Siberia, the Hartz, and Cornwall. Iodide of silver occurs in various parts of the New World*; at Abarradon, in Zacatecas, it is found in thin veins in steatite. Bromide of silver is so abundant in the district of Plateros, Mexico, near Zacatecas, that the ores have received the name of plata verde, from the colour it causes them to assume.

2. ORES CONTAINING SILVER IN A VARIABLE PROPORTION, AND NOT AS AN ESSENTIAL CONSTITUENT.

Sulphuretted ores are always richer in silver than oxidised ores; the ferruginous sulphides are usually the poorest, and next come the sulphides containing zinc, lead, and copper. Of these ores the following may be mentioned :a. Argentiferous Lead Ores.

Galena, PbS, containing between o'01 and 0'03 per cent of silver, often, also, o ̊5 per cent, but seldom as much as I per cent. According to Malaguti and Durocher, some of the galena of Rhenish Prussia contains upwards of 7 per cent of silver (Schemnitz). The ores of Joachimsthal, which average among the highest in Europe, generally contain about 2. or 3, and seldom exceed 10, per cent of silver. The average of the region about Clausthal is o'098 per cent, and that of Andreasberg is 0.36 per cent. The Saxon galena averages between 0'025 and 0.809 per cent of silver.

White Lead Ores, containing traces up to o'002 per cent of silver.

b. Argentiferous Copper Ores.

Fallow Orest containing from traces up to 31 per cent of silver.

Copper Pyrites, Variegated Copper Ore, and Copper Glance, are generally poor in silver. Bournonite is somewhat richer.

Oxidised Copper Ores mostly contain mere traces of silver; sometimes they are richer, for instance, malachite ores at Bouc, in France, contain o ̊525 oz. of silver and 0'0035 oz. of gold per cwt.

* B. u. h. Ztg., 1859, p. 452; 1860, p. 187; 1861, p. 308.

+ KARSTEN'S Archiv., 2 R., iv., 289. ERDMANN'S J. f. k., öu. techn. Ch., x. 219.

c. Argentiferous Zinc Ores.

Zinc Blende contains sometimes as much as o'88 per cent of silver. Blende at Poullaouen contains o'019; at Huëlgoet, o'008; at Przibram, from o'0027 to 0'0067; at Fahlun, o'005; at Sala, 0'0033; and at Tunaberg, o'oor per cent of silver. Blende in Hungary, Saxony, and Kongsberg contains mere traces. If zinc blende occurs with galena, sometimes the former, and sometimes the latter, will contain most silver; for instance, at Poullaouen the blende contains 0'004 and the galena o'025; at Huëlgoet, the galena o*125, and the blende from o'002 to 0'004 per cent. The pure blende of Lautenthal contains o'o008, and that of Freiberg 0'0006 per cent. Sometimes blende occurs richer in silver; for instance, the blende of Pontpéan* (Bretagne), contains from 350 to 52'5 ozs. of silver per ton, from 5 to 8 times as much as the galena associated with blende contains. This blende is worked at Swansea.

Calamine from Altenberg contains o'ooo1 per cent of silver.

d. Argentiferous Iron Pyrites.

They contain from traces up to 0.00150 per cent of silver, and are poorer than other sulphides if they happen to be associated with them.

e. Argentiferous, Arsenical, and Antimonial Ores.

Native Arsenic from Markirch (Upper Rhine) contains 0'00092, and that from Adreasberg (Hartz) o'005 per cent of silver.

Mispickel sometimes contains o'0038 per cent of silver. Native Antimony from Andreasberg contains 1 per cent of silver, and that from Allemont o'0004.

Dressing the Silver Ores.

Ores of the first class seldom occur in large quantities, and are mostly disseminated in the gangue (Dürr ores), requiring a most careful preparation; and it depends on local circumstances whether it is advantageous to concentrate the

* Revue Univers., 1863, 2 livr., page 294. Bulletin de la Société de l'Industrie minérale, tom. viii., livr. 4. 1863.

amount of metal so as to cause loss of silver but saving of fuel in the smelting process, or to work a larger and poorer quantity with a larger consumption of fuel. Ores containing much baryta have lately been prepared by heating them with coal and washing out with water the sulphide of barium formed.*

Ores of the second class are usually first sorted as perfectly as possible by hand, partly to facilitate the dressing of the ores and partly to prepare them for a suitable metallurgical process, as, in most cases, it is not possible to smelt the ores in the proportions in which they occur in nature. How far hand separation is to be carried on, as well as the farther dressing of the separated ores, depend on the requirements of the metallurgical process, which will in some cases aim at the production of the accompanying metals (lead, copper), or the extraction of silver from those metals (for instance, zinc, arsenic, antimony, bismuth). And as the value of the silver is in many cases much the highest, its extraction is effected at the expense of the copper which is present.

SYNOPSIS OF PROCESSES FOR THE EXTRACTION OF SILVER FROM ITS ORES.

The great variety of ores in which silver occurs usually makes it necessary to employ complicated processes for its extraction.t

A. EXTRACTION OF SILVER, IN THE DRY WAY, BY MEANS OF LEAD.

By fusing argentiferous substances with metallic lead, or by smelting such substances together with lead, lead products or lead ores (when the silver ore does not already contain a sufficient amount of lead), an argentiferous raw lead is produced; this lead is either cupelled or, if containing but little silver, is previously treated by Pattinson's process. The silver resulting from the cupellation process is refined by another process, which produces fine silver. It depends on

* Oesterr. Ztsch., 1862, No. 464; 1863, No. 1. B. u. h. Ztg., 1863, p. 114, 269. + KARSTEN'S Archiv. 2 R., xxv.; 174. B. u. h. Ztg., 1852, p. 73, 815.

the amount of silver present, on the price of materials, &c., whether it is advisable to desilverise the ores at once or the intermediate products (matt, raw copper, &c.)

These processes are very old, and applicable to argentiferous substances of every kind; but they are mostly imperfect on account of their complications, producing more or less intermediate argentiferous products, whose farther treatment requires much time and a great consumption of fuel, and causes a great loss of metal.

Many of these processes have, therefore, lately been replaced by more perfect processes in the wet way. The choice of a process is chiefly influenced by the nature of the ores and local circumstances, such as whether lead ores are cheap or totally absent. Lead, for instance, is most valuable for treating auriferous silver ores and products, as it extracts silver and gold at the same time, which can only be very imperfectly effected by other means. Only lately, Patera and Roessner have discovered how to extract gold and silver in the wet way, by means of a solution of chloride of soda saturated with chlorine.

The following ores are submitted to treatment with lead :1. Argentiferous Galena, from which the greater part of our silver is obtained. The processes adopted are described in Chapter I. (Lead). They are the oldest,* and generally the simplest, for which the amalgamation process may be advantageously substituted in rare cases only, as, for instance, if fuel is not easily procurable, as in Nicaragua.f The less copper the ores contain the more easily and perfectly the silver may be extracted.

2. Silver Dürr Ores, mixtures of real silver ores with earthy, sulphuretted substances, &c. (Dürr ores containing earths, pyrites, blende, copper).

Rich earthy Dürr ores, if they contain chiefly native silver, are sometimes smelted together with lead products in crucibles (formerly at Kongsberg), or they are refined at once with an addition of litharge (now at Kongsberg); and if they consist of other ores, with from 50 to 90 per cent of silver, it is

Bgwkfd., xii., 590.

+ B. u. h. Ztg., 1862, p. 268.