b. In floors. In the mountain limestone of the Western United States. This limestone belongs to the Upper Silurian formation; and in its lower part is siliceous, in its upper part dolomitic.

D. IN DEVONIAN SLATES.

a. In veins. In the lower slates (in the mountains of the Rhine near Trier, Coblentz, and Aix-la-Chapelle, in Nassau, on the right bank of the Rhine, Grand Duchy of Hessia, Andreasberg on the Hartz); in floors (Rammelsberg near Goslar).

b. In the intermediate slates. In veins, in Lenneslate and Eifel limestone (Cologne and Arnsberg); in beds (Meshede, Brilon, and Aix-la-Chapelle); in nests (district of Aix-laChapelle and Brilon, Iberg near Grund on the Hartz); in irregular masses (Breinig near Stolberg).

c. In the upper slates. In veins (Stolberg near Aix-laChapelle).

E. In COAL FIELDS.

a. In carboniferous limestone. In veins (Stolberg near Aixla-Chapelle, district of Dusseldorf and Elberfeld); in lodes (Derbyshire and Cumberland); in irregular masses (district of Dusseldorf and Elberfeld).

b. In bituminous shale. In veins, (Upper Hartz, district of Arnesberg, Province Upper Hessia, Vosges, Poullaouen and Huelgoet in Bretagne, Culera in Catalonia); in contact groups (Christiania).

c. In carboniferous formations without coal. In veins (Gablau, in the district of Landshut; Esshoff, in the district of Brilon).

d. In the carboniferous formations containing coal. In veins (Horst on the Ruhr, district of Waldenburg); in Silesian coal fields; in porphyry.

F. In the Permian formation. In some copper-slate; in the cupriferous shale near Gelnhausen in Prussia; in bituminous dolomite near Frankenburg; in the ash near Lauterberg; in the Hartz.

G. In the TRIASSIC FORMATION.

a. In Vosges sandstone. In veins (Katzenthal near Lembach in the Vosges).

b. In new red sandstone. In veins (Bavarian Pfalz, Baden

weiler in the Black Forest); in bunches, and in nests (Commern, Maubacher, Bleiberg near Düren).

c. In shell limestone. In beds (Reifelfingen and Bruchsal in Baden); as impregnations (Tarnowitz); in floors (Wiesloch, Tarnowitz, Olkusz in Polonia).

d. In Keuper. In nests, or impregnated in sandstone (Freiberg in Bavaria).

H. In the JURASSIC FORMATION. In veins (near Blankerode, in the district of Büren near Minden); impregnated, in beds, and in floors, in dolomitic limestone, and in ferruginous clay (Santander in Spain).

K. IN TERTIARY ROCKS. In nests and in clay (Tarnowitz, Beuthen).

Galena occurring in veins is associated with either earthy minerals (quartz, calc spar, fluor spar, heavy spar), or with metalliferous minerals (blende, iron pyrites, sparry iron ore, arsenical and antimonial substances, &c.); sometimes it is associated with copper, zinc, silver, cobalt, and nickel ores. Malaguti and Durocher found silver in blende occurring in lead veins, from traces up to o'88 per cent, and also traces in all the iron, copper, and arsenical pyrites which they submitted to examination. They also found that pure sulphuretted ores were always richer in silver than oxidised ores. Iron pyrites associated with galena sometimes contains gold (Hungary, Freiberg, Rammelsberg, Lautenthal on the Hartz). The commoner metals-iron, lead, zinc, and copper-are very frequently found together.*

Lead ores occurring in beds, nests, floors, &c., are usually poorer in silver, but they contain a less proportion of other earthy and metallic minerals than those in veins. The deposits in the Rammelsberg form an exception to this.

2. White Lead Ore (carbonate of lead), PbO, CO2, containing 77'52 per cent Pb. If in admixture with clay, oxide of iron, &c., it is called bleierde (oxidised lead), and if mixed with coal, black lead ore. Of the oxidised lead ores the carbonate is the one which most frequently occurs; it is mostly found on the head of lead ore lodes, and is a secondary forma

BREITHAUPT, Paragenesis der Mineralien, Freiberg, 1849. ELIE DE BEAUMONT, Vertheilung der Elemente in der Natur. LIEBIG'S Jahresber, 1849, p. 785.

tion derived from galena by atmospheric influence. In case the galena contains silver, a small amount of the latter (seldom more than o'r per cent) will pass over into the white This ore sometimes occurs together with copper and iron pyrites, and also with various oxidised and sulphuretted metals. It is seldom found in large masses, and is mostly worked and smelted with galena. The most important localities where it occurs are at Diepelinchen near Aixla-Chapelle, where the ore is found in nests in the Devonian rocks, and, together with bitumen, quartz, clay, and carbonate of zinc, in coal formations; in the Eifel mountains, where the ore occurs above the head of the new red sandstone, or as disseminated grains (Commern, Düren), or in layers and masses mixed up with clay; in the clay schists of the new red sandstone (Scheiden); it is furthermore found in different parts of Spain, as, for instance, in the province of Santander, mixed with calamine, clay, limestone, and dolomite; lead ores containing silver are found in quartz on the Altai mountains, associated with white lead ore, iron ochre, and other minerals; great quantities of this ore are also found in the Mississippi valley.

3. Sulphate of Lead, PbO,SO,, containing 68.3 per cent Pb, is very rarely found in masses worth working. It occurs at Pallières near Alois, above galena lodes, but is poor in silver; also at St. Martin near Vega de Ribaddeo in Spain, together with phosphate of lead; and in the mines. of Australia, where it contains, on an average, 35 per cent of lead and 35 ounces of silver to the ton, besides a small amount of gold. Sulphate of lead contains more silver than galena does.

4. Pyromorphite, PbCl +3PbO (PO, As O), containing 69.5 to 76.2 per cent Pb, and never more than traces of silver. Some large deposits of this ore occur at Stolberg near Aixla-Chapelle; at Ems; and at St. Martin in Spain, where it assumes the form of grapes.

5. Yellow Lead Ore (molybdate of lead), PыO, MoO3, containing 57 per cent Pb. It is only found in association with other sulphuretted and oxidised lead ores; as at Bleiberg in Kärnthen, in some parts of Bavaria, &c.

SYNOPSIS OF PROCESSES FOR THE EXTRACTION OF LEAD FROM ITS ORES.*

THE extraction is done in hearth and cupola furnaces, and in reverberatory furnaces, either by a combined smelting process of oxidation and reduction, or by reduction and precipitation, the latter being always combined with some kind of purifying process. The particular process which should be adopted in any case, depends greatly on the price and quality of the smelting ingredients, such as the fuel, and also in a great measure on the quality of the ores, -whether they are in a sulphuretted or in an oxidised state; whether they are free from foreign sulphates and earthy substances; whether or not they are rich in silver, &c. In many cases, metallurgical traditions, and the industrial and commercial habits of different countries, are considered sufficient reasons for not introducing a more rational mode of operation than that which happens to be in use.

Influence of Foreign Substances contained in Lead Ores.

Foreign substances (sulphides and metalliferous minerals) occasion;

a. Loss of lead; by facilitating the formation of metallic fume in the furnace (sulphides of zinc, arsenic, and antimony); by rendering the ores more difficult of fusion (zinc blende); by forming sulphurous slags which are capable of retaining valuable metals, such as silver, copper, &c. (zinc blende); or by causing the ores to cake during roasting (sulphide of antimony in the reverberatory process) &c.

b. Deterioration of the lead (antimony, arsenic, and copper).

c. Deterioration, and a loss of lead at the same time by volatilisation (antimonial and arsenical compounds).

* Du Plomb, de son Etat dans la Nature, de son Exploitation, de sa Métallurgie et de son Emploi dans les Arts, par LANDRIN. Paris, 1857. (B. u. h. Ztg., 1867, p. 332.) Métallurgie du Plomb et de l'Argent, par Rivor. Paris, 1860. Rudimentary Treatise on the Metallurgy of Silver and Lead, by LAMLondon, 1861.

BORN.

d. A favourable influence may be exerted by the presence of silver in galena, also of sparry iron ore and iron pyrites, after roasting, during the reduction pro

The latter mineral exerts an unfavourable influence in the precipitation process. As most lead ores contain enough silver to make its extraction profitable, the process to be selected for the reduction of lead depends upon the method adopted for the extraction of the silver. These processes will be more fully explained in a subsequent chapter.

Earthy substances may exert a different influence, depending solely on their nature, such as whether they are basic or otherwise. Sometimes they are necessary for the formation of slags; in other cases they act very favourably (as lime does, in the reverberatory process); and in some particular cases their influence is positively deleterious (as, for instance, silica in the reverberatory process).

In the Preparation of the Ore it is of importance to take into consideration the influence of foreign substances, and accordingly to carry out the dressing, i.e., mechanical purification, to a greater or less extent. The richer the ores are concentrated, the less cost and loss of lead will be occasioned in smelting; but this preparation can only be effected with a great sacrifice of ore, especially if it contains much silver, and if the latter is derived, not from isomorphous sulphide of silver, but from disseminated silver ores, which are mostly of less specific gravity than lead ores. It is therefore advisable to separate galena poor in silver, more completely from its earthy and metallic impurities than galena rich in silver. The economical limit of the concentration of ores is to be ascertained only by extensive, exact, and tedious trials; and such limit depends in each case on the quality of the ore, as well as on local circumstances. Rivot* has given suggestions for such experiments. Of the metallic impurities in galena, the Copper Pyrites is separated with difficulty, and with considerable loss of lead and silver; in consequence of this, the lead and Traité de Métallurgie, tom. ii. Métallurgie du Plomb et de l'Argent, 1860, p. 4.