USES OF ZINC
Metallic zinc, or spelter, as the commercial metal is often known in the trade, is chiefly used in the form of rolled sheets; in galvanizing; in alloys forming brass and bronze; and in the desilverization of lead bullion. Rolled sheets are used for roofs, tanks, conduits, and protective linings. Iron and steel objects are dipped into baths of molten spelter and coated with the metal or galvanized, being thereby protected from oxidizing agencies. Other methods of applying this protective coating are also in use.
Zinc and copper unite in all proportions, forming alloys known as brass which are of widespread industrial application. There is only one definite alloy; it corresponds approximately to CuZn2, contains 33 per cent. copper and 67 per cent. zinc, is hard and brittle and of little practical value. All other brasses may be considered as solid solutions of this definite alloy in an excess of one of its constituents. Brasses in use vary in zinc content from 20 to 85 per cent. and differ greatly in their properties according to the composition. Alloys of zinc and aluminum have valuable properties, especially those containing 25 to 35 per cent. zinc. Other alloys used contain, besides copper and zinc, either lead, tin or nickel.
The Parkes process of desilverizing lead bullion has superseded the older Pattinson and cupellation process, except where bismuth is present, owing to the avidity with which zinc robs the bullion of gold, silver, copper and tellurium. This purification may be made as perfect as desired or only to a commercially profitable point, generally being brought down to a content of one-half ounce of silver per ton of lead.
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.