Among the miscellaneous uses of zinc are these: ornamental castings; in galvanic batteries; in photo-engraving; in plates hung in boilers to prevent formation of scale; precipitation of gold in the cyanide process; in the form of powder, as a reducing agent in organic chemistry, especially in the reduction of indigo-blue and in a paint for structural steel. Zinc is also used in the form of numerous salts, such as the chloride as a wood preservative, and the sulphate, employed in medicine, dyeing and glue manufacture.
Zinc oxide, produced both from the metal and from ores, is used as a pigment both in combination with white lead and barytes, and as a competitor of them. Considerable amounts of oxide are also used in the rubber manufacturing industry. Lithopone (an intimate mixture, obtained by chemical precipitation of zinc sulphide and barium sulphate) is of growing importance as a pigment.
All the chief uses of zinc, comprising galvanizing, rolled sheets, brass-making and the desilverization of lead bullion, may be considered essential. Brass belongs with steel in the category of indispensable materials of modern industry. No satisfactory substitute as regards both physical qualities and cost is available for many important parts of machinery and for manufacturing purposes. Its wide use depends on a number of qualities. The excellent sharp castings made from certain brasses are readily machined or otherwise finished and electro-plated if desired. The electrical conductivity of brass is good. Certain brasses are easily rolled into sheets and cut and stamped in desired shapes. Lubricated surfaces of steel on brass make satisfactory and durable bearings.
The other large uses of zinc depend on its resistance to oxidation and on the possibility of rolling it into fairly thin sheets. In both these qualities, however, it is surpassed by other metals, notably nickel and tin. Alloyed with lead it may be rolled into a substitute for tin-foil. It is in some cases a fairly satisfactory, cheap substitute for metals of higher quality. In times of scarcity or high prices, substitution of metals of inferior quality is feasible, and in many cases zinc may be temporarily dispensed with altogether. Its field is therefore largely fixed by commercial conditions of supply and price, which determine broadly the total consumption and especially the percentages devoted to the various uses. It may be assumed, however, that the percentages for the domestic consumption in the United States in 1910 represent approximately those of normal peace times. In that year, of the total consumption, 60 per cent. was used in galvanizing; 20 per cent. in brass-making; 11 per cent. in rolled sheets; and 1 per cent. in lead desilverization; leaving 8 per cent. for miscellaneous uses. During the war the percentage used in galvanizing was greatly reduced and that used for brass-making much increased. The use of rolled sheets will increase.
A large part of the European production in normal times is rolled into sheets used chiefly for roofing.
CHANGES IN PRACTICE
In the extraction of zinc from its ores the most important changes in practice during recent years have been adaptations of retort smelting for the purpose of utilizing zinc concentrates from complex ores, the increased production of zinc oxide and lithopone through the application of volatilization methods to the re-treatment of retort residues and base ores, and the electrolytic and electro-thermic processes of extraction of the metal.
The most revolutionary advance has been the development of the oil flotation, the electro-magnetic, and electro-static processes for the concentration of ores. These processes are being widely introduced and in connection with electrolytic reduction are particularly adapted to the production of spelter of the highest quality from complex ores. As the electrolytic and electro-thermic processes find their field only where power is relatively cheap, the tendency is to put installations where hydro-electric power is available, effecting a redistribution of zinc-smelting centers.
GEOLOGICAL DISTRIBUTION
Zinc and lead are commonly associated in mineral deposits, sometimes intimately mixed, sometimes so segregated that one metal predominates, but ores of one are seldom free entirely from the other. The geological and geographical distribution of the two metals is therefore nearly identical.