Besides the alloys in which zinc forms an essential ingredient (pp. 13-17,20-1,29-30,34-5,42), there is an immense consumption for coating iron plates to produce what is known as "galvanized" iron. Zinc is used by engineers chiefly as roof covering, the sheets being made 7 ft. or 8 ft. lung and 3 ft. wide. The sheets are stiffened and jointed by lapping over wooden rolls,and are sometimes laid on boarding. The thickness of the sheets is designated by a special gauge, which does not coincide with the B.W.G., and it is best to specify the thickness by the weight per sq. ft. Light sheets of No. 13 gauge, weighing about 16 oz per ft., are sometimes used, but for good work Nos. 14 and 15, weighing 19 oz. to 22 oz. per ft., are generally preferred. The durability of zinc depends mainly on the purity of the spelter from which it is rolled, and the cost is about 3/. per ton above the price current for spelter. The wooden rolls used with the sheets cost about 10s. per square of roofing surface, and packing for shipment costs about 30s. per ton.

Zinc Ores Part 3 300199

Fig. 183.

Zinc Ores Part 3 300200

Production

The total production of zinc in Europe attained 203,330 tons in 1880, of which Germany produced 99,405 tons, or nearly half, about two-thirds of which were extracted from Upper Silesia. After Germany comes Belgium with 65,010 tons, then England with 22,000 tons, France 13,715, and Austro-Hungary 3200.

Decorating

A beautiful and permanent dark or light green coating, resembling enamel, can be applied to all kinds of zinc articles, especially those made of sheet zinc, in the following manner:-5 oz. soda hyposulphite are dissolved in 50 oz. boiling water, and the solution is poured at once, in a fine stream, into 2 1/2 oz. strong sulphuric acid. The milk of sulphur that separates will soon ball together in lumps and settle. The hot liquid containing soda sulphate and sulphuric acid is decanted, and the cleansed zinc is put into it. In a short time it will acquire a very brilliant light-green coating of sulphide, and only needs to be washed and dried. By exposing it repeatedly and for a longer time to this hot bath, the coating grows thicker and the colour darker and more brilliant. The temperature must not fall below 145° F. (63° C); when it does, the solution should be heated up to 190° F. (88° C), to obtain a fine and brilliant deposit. By dipping these articles in dilute hydrochloric acid, 1 of acid to 3 of water, sulphuretted hydrogen is evolved, and this enamel-like coating loses its lustre and gets lighter in colour. Aqueous solutions of aniline colours have little effect upon this dull surface, and none on the grey brilliant coating.

The effect of marbling can be obtained by moistening the grey zinc and applying hydrochloric acid in spots with a sponge, then rinsing it off, and while still wet flowing over it an acidified solution of copper sulphate, which produces the appearance of black marble. As the zinc has generally a dull surface, it must receive a coat of copal varnish. If-1 1/2 oz. chrome alum and 1 1/2 oz. more soda hyposulphite be added to the solution, the article will have a brownish colour. - C. Puscher, Ding, Pol. Jl.