ZINC. Zinc cast Mt° slabs as it comes from the furnace is commercially known as spelter, but zinc recast into forms such as are used in galvanic lotteries is known as battery zinc, and zinc rolled into sheets is known as sheet zinc. There is a growing movement, fostered by the American Zinc Institute, to avoid confusion by abandoning the use of the word spelter.
Properties.— Zinc is a bluish-white metal with a bright metallic lustre, an atomic weight of 65_37, a density of about seven, and a bard ness, when cast, of 38 in the Brinell scale, as compared to a hardness of 40 for copper and a for silver. Both density and hardness are slightly increased by rolling. It is so hard that it can be 6kd with difficulty, and in a large mass it can be broken only with considerable force. Its texture as shown on a.bsokeo sur face is prismatic crystalline, the crystals being six-sided and belonging to the hexagonal-i tem. At different temperatures zinc has thf ferent properties. At ordinary temperatures it is fairly brittle, but at l00'-150°C it can be rolled out into sheets or drawn into unre, though above 200° C. it becomes brittle again. It melts at 419.4° C and boils at 920' C. the vapor burning in air with a characteristic bril liant bluish-green flame to zinc oxide, formerly known as 'philosopher's wool' or flowers of zinc.' Zinc is not affected by dry air or by oxygen at ordinary temperatures, but under most atmosphenc conditions the surface be comes covered with a coating of grayish-whim basic carbonate of zinc, which protects the metal from further corrosion. The industrial value of zinc for use as a protective coating for iron and steel and for use in exposed positions is doe this property tux is used in metallic form in pl vanizing iron and steel, in making sheet zinc. and in making brass and some other alloys. Iron and steel may be galvanized in several ways — by dipping the articles in a bath of molten zinc; by heating them to 425'-450° C in a drum filled with zinc dust, a process known as *sherardixing," in which they are coated with zinc by the zinc vapor given off from the zinc dust; and by electroplating them with zinc. As only the last method employs the
galvanic current, the others are miscalled 'gal vanizing,' and an article protected by a coat of zinc would better be called 'zinc-coated.' In normal times about 60 per cent of the zinc out put of the country is used in zinc-coating iron and steel. Metallic zinc may be rolled in plates an inch or so thick —'boiler plates,' which. suspended in boilers, preserve than from the corrosion of sea water — or in thinner sheets for roofing, shingles, gutters, spouts, house hold utensils, zincographer's plates, dry bat teries, buttons, shoe-lace tips, etc. Much sheet zinc was used during the European War to line packing cases filled with munitions and machined parts which needed protection from the sea air. Metallic zinc is alloyed with cop per to form brass, some 'bronzes' and other alloys. In normal times only about 3) per cent of the total consumption is used in making brass, but during the European War the greater part of the metallic zinc produced in the country was used for that purpose_ A considerable quantity of metallic zinc is used annually in desilverizing lead by the Parkes process.
Zinc oxide is made under the French process by burning metallic zinc in an oxidizing atmosphere, and under the American process by burning oxidized or desulphurized zinc ores mixed with ground coal in an oxidizing atmos phere. The purity of the product depends on the parity of the metal and the ore. Omar calls- pure zinc oxide is used in pliannacratica: preparations. Zinc oxide of good grades free from lead is also used largely in making rut ber, to increase its tensile strength, It and increase its wear-resisting properties. Zinc oxide of both good and common grades is used as a pigment in making paints. American process oxide, in which there is a considerable percentage of lead, i.e., leaded zinc oxide, is also used for pigment, as a combination of lead and zinc is held to be desirable in a paint.