other products obtained from smelting cupriferous galena will be also cupriferous; and as in most cases they also contain silver, these metals must be extracted by separate processes.

Iron Pyrites is also somewhat difficult to separate, but it very rarely acts perniciously; sometimes it has a disadvantageous influence upon the melting mixture by augmenting its amount of sulphur (precipitation process); but, in most cases, a certain amount of iron pyrites in galena is advantageous (roasting reduction process). If iron pyrites is disseminated through galena, some part of it may be separated by hand sorting, but this cannot be effected by the ordinary dressing process.

Grey Copper Ore and Bournonite render the resulting lead impure, and facilitate its volatilisation, but they admit of an advantageous extraction of copper; the firstnamed mineral also assists in the extraction of silver. The greater the amount of silver the less the dressing is to be carried on, on account of the small specific gravity of the fallow copper ores. In the melting process antimonial and arsenical products are formed, which are difficult to roast, owing to their easy fusibility; and the metals contained in them can be extracted only with great loss.

Blende, under all circumstances, has an injurious influence upon the melting process, and can be only partly separated from galena, on account of its great specific gravity. This is also the reason that the dressing of galena, when associated with blende, and poor in silver, may be carried on further than when the galena is rich in silver. Galena containing 15 per cent of blende may still be worked advantageously in reverberatory furnaces. If galena contains more than this amount of blende, it should be smelted in cupola furnaces, though in this process also, blende occasions loss of lead and silver by volatilisation, by a formation of fume in the furnace, and by rendering the slags, &c., more difficult to fuse.

Sulphide of Antimony is often found so finely disseminated through galena that its separation by a mechanical process is impossible, and it occasions loss of lead and silver in the melting process on account of its volatility; it also renders the

working of the resulting intermediate products difficult (for instance, the cupelling of the raw lead), and it renders the pig lead impure. Antimony is equally injurious whether the ores are smelted in reverberatory or in cupola furnaces. Arsenical Pyrites behaves in a similar manner.

Of the earthy associates of galena, Calc Spar and Fluor Spar are the most important; these are seldom much disseminated in it, and, in most cases, can be separated mechanically without loss of metal; they also frequently exert a very favourable influence upon the melting process: indeed, in some cases, when galena does not already contain them, they should be added.

Quartz is often found accompanying galena; and this mineral, as well as aluminous substances, causes the more loss of metal the finer the ore has to be pulverised for its preparation, and in many cases they cannot be separated sufficiently to become innocuous in the reverberatory process.

Heavy Spar is very difficult to separate from galena on account of its great specific gravity, and it is not possible to prepare ores containing it sufficiently pure for the reverberatory process without great loss of metal. The economical working of these ores can therefore, in most cases, be only effected when the sorting is done by hand. An amount of 15 per cent of heavy spar in galena renders the reverberatory process difficult. If such ores are worked in cupola furnaces, the heavy spar acts disadvantageously, by augmenting the mass, and thus occasioning the use of an increased amount of fuel.

Oxidised Lead Ores, in association with earthy substances, can be dressed without difficulty, but they occasion great loss if they are associated with galena. In rare instances only are they so rich in silver that any considerable mechanical loss of it may take place in the preparation. This may happen if clays containing silver occur together with lead ores.*

* Bulletin de la Société de l'Industrie Minérale, iii. 287.

The chief modes of extracting lead from its ores, at present adopted, may be classified under the two following divisions:

I. SMELTING OF SULPHURETTED LEAD ores.

a. The Reverberatory Process is used, in general, for ores rich in lead, and poor in foreign sulphides and earthy matters, and especially silica; it is not often employed, and only for the treatment of ores containing much silica, when fuel is cheap (French precipitating process). It may be subdivided into-1. Roasting reaction processes, which consist in the removal of the sulphur, partly by roasting and partly by the reaction of the oxidised substances in the mass upon the sulphuretted ones; the following are modifications:-The Carinthian Process, used for very pure ores, free from silica. These ores are treated in small quantities, in reverberatory furnaces with inclined hearths, from the bottom of which the reduced lead (as chief product) continually runs off, whilst a smaller quantity of lead is obtained by mixing coal with the residues, which are rich in oxide. This process is adopted at Bleiberg in Carinthia, Holzappel, Graubündten, and in Spain. The English Process is employed for calcareous ores rich in lead; upon treatment of the larger bulks in reverberatory furnaces furnished with a sump, metallic lead, subsulphide and oxysulphide of lead will be formed; the two latter are decomposed by lime and coal. This process is in use in England, Spain, and was tried in the Hartz. The French Process is adopted for ores containing pyrites and some silica; upon treatment in reverberatory furnaces with a sump, little lead and a great deal of oxide of lead are formed, the latter being reduced by coal. This process is employed at Poullaouen, Pezey, Corfali, Stolberg, and Tuscany, and the smelting works on the Rhone. It is also tried on the Upper Hartz. 2. French Precipitation Process. In this the siliceous galena is decomposed by iron. It is employed at Vienne, Poullaouen, Corfali, and Tuscany, and the smelting works at Marseilles.

b. The Hearth Furnace Process is used for very pure galena, when fuel is expensive, or of inferior quality; the reactions are similar to those in the English reverberatory process.

There are two modifications of this process. The first is, smelting in North American hearth furnaces with hot blast; in this only the very purest galena is used. It is generally adopted in North America, and it has been tried at Bleiberg, and Przibram. The second is, smelting in Scotch hearth furnaces with cold blast; the galena used need not be pure, but should be free from silica, and previously roasted in reverberatory furnaces. This process is in operation in Cumberland, Northumberland, Durham, and Pezey.

c. The Cupola Furnace Process is used for galena containing a larger amount of foreign sulphides and earths, or silica, and which is suited neither for the reverberatory process nor for that in hearth furnaces. Pure galena is seldom used. This process is subdivided into-1. Precipitation Process. In this the unroasted earthy galena is decomposed by metallic iron; the galena must be as free as possible from foreign sulphides (Upper Hartz, Victor-Friedrichs-hütte, Joachimsthal); the decomposition is effected by ferruginous fluxes: -by iron ore (Ruszkyberg); by iron cinders produced in the refining process (Kinzig-thal); by roasted raw matt (Sala); by ferruginous lead matt slags (Clausthaler, trials with the reverberatory furnace); and by such fluxes in combination with metallic iron (Tarnowitz, Przibram, Münsterthal, Ems). 2. Common Lead Process. Used for smelting galena containing a larger amount of foreign sulphides, and more or less earthy matter; it is seldom employed for melting purer and only earthy lead ores (Commern, Stolberg). The opera tions are:-Roasting in heaps (Lower Hartz, Müsen, Rothenbach); in mounds (Fahlun, Rhone smelting works); or in reverberatory furnaces (Przibram, Freiberg, Commern, Stolberg, Lower Hungary, Holzappel, Pontgibaud, Vialas, Rhone smelting works, Tuscany, Spain); reducing and purifying smelting of the roasted ore in cupola furnaces, with or without ferruginous fluxes, or with such fluxes in combination with metallic iron; the details depend on the quality of the ores, and the price of the smelting materials. There are the three following subdivisions of the common lead process : the first is adapted for the working of ores poor in lead and very siliceous, by roasting and reducing without ferruginous

fluxes (Lower Hartz, Fahlun). The second is employed for the working of siliceous and earthy ores richer in silver, by smelting them, after roasting, with ferruginous fluxes; with ores containing crude matt (Lower Hungary); with roasted raw matt (Freiberg); with iron ore (Vialas); with refinery cinders (Tuscany, Spain, Rhone smelting works); or with such fluxes in combination with metallic iron (Przibram, Holzappel, Musen, Rothenbach, Pontgibaud). The third modification is employed for working earthy ores richer in lead, by roasting and smelting with iron ore (Commern), or with refinery cinders (Stolberg).

2.-TREATMENT OF OXIDISED ORES AND PRODUCTS.

a. White Lead Ores.-Reduction smelting of rich ores in reverberatory furnaces, and of poor ores in cupola furnaces (Altai, Münsterbuch, near Stolberg, Southern Spain), or in air furnaces (Southern Spain).

b. Sulphate of Lead.-Working in reverberatory furnaces (Poullaouen, processes of Rivot and Phillips, and Völckel), and in cupola furnaces (Southern France).

c. Litharge.-Reduction in reverberatory furnaces (England, Holzappel, Ems, Poullaouen); in cupola furnaces (Upper Hartz, Lower Hartz, Freiberg, Przibram, Tarnowitz); in Siberian hearth furnaces (Barnaul, Freiberg, Fernezeley); in Scotch hearth furnaces (Tuscany, Pontgibaud, Pezey).

d. Dross.-Melting the dross in reverberatory furnaces, and producing hard lead in cupola furnaces (Upper Hartz, Lower Hartz, Przibram, Freiberg, Holzappel, Müsen, &c.)

e. Bottoms of Lead Furnaces.-Melting in reverberatory furnaces (Siberia), and in cupola furnaces (Tarnowitz.)

f. Lead Slags.-Melting in reverberatory furnaces for producing raw matt (Freiberg), and in cupola furnaces for producing lead (Tarnowitz, Hettstadt, Sardinia, Spain).

The raw lead produced from any of these ores or products is refined by various processes. The following are those generally adopted :-Skimming off the dross (Upper Hartz, Lower Hartz); stirring with wood shavings (reverberatory process in England, France, &c.); stirring with wooden poles (Altenau Lead Works, Ramsbeck); Pattinson's process