Zinc chat, which consists of minute droplets of metallic zinc coated with a film of zinc oxide, is formed in the distillation of zinc, or is specially prepared. It is a very active chemical agent and is used to discharge the color of the pat tern in calico printing. It is also used to precipitate gold in the cyanide process of gold recovery and to precipitate other metals and purify the solution in making lithopone and in the electrolytic deposition of zinc. Another use is in sherardizing as mentioned above. Litho pone, a chemical combination of zinc sulphide and barium sulphate, is a white pi t used for interior paints and forms the pigment of mostwhite enamels. Several salts of zinc are em ployed in medicine and the arts. Zinc acetate and zinc sulphate are used in medicine as an emetic, astringent and antiseptic. They arc used as a mordant in dyeing, and are also use ful in wood preservation, hut the chloride is generally employed for that purpose, as in the Burnett process. Zinc chloride is used as a caustic agent in the treatment of certain dis eases, as a general disinfectant and preserva tive, and as a flux in soldering. Zinc sulphate is used in bleaching paper and as a dryer in varnishes and in fireproofing paints.
The chief zinc minerals are zinc sulphide, sphalerite (zinc hlende or 'black jack') ; zinc carbonates, smithsonite (calamine in Europe) and hydrozincite; zinc silicates, calamine (smithsonite in Europe) and wille mite; zinc oxide, zincite ('red zinc ore*); and zinc-iron-manganese oxide, franklinite. The three minerals last named form the ore at Franklin Furnace mines, in New Jersey, where they occur more plentifully than anywhere else in the world. Zinc Mende is the most common ore of zinc. It usually occurs as a complex ore in association with galena and with pyrite and other metallic sulphides, but in the Mascot mines of eastern Tennessee it is unassociated with either lead or iron. The upper parts of sulphide deposits containing zinc have usually I eeti altered ht oxidation, and the zinc minerals Manliest to the silicate and carbonate. The principal zinc-producing region in the United States is the Joplin district, comprising south western Missouri, southeaqern Kansas and northeastern (/klationia. which in 1917 pro duced ores containing 23•,676 short tons of recoverable zinc, about 34 per cent of the total production of the country. The Franklin Furnace mines produced 119,736 tons of re cocerable zinc, or 17 per cent of the total, the Butte district of Montana produced 90,145 tons, or 13 per cent, and the upper Mississippi Val ley district of ‘1"isconsin, Illinois and Iowa pro duced 64,027 tons, or 9 per cent. Other im portant zinc districts are the (*trim d'Alene district of Idaho, the Leadc-ille district of Colorado the east Tennessee district and the Yellow Pine district of Nevada The total recoverable zinc content of zinc ores mined in the country in 1917 %%as 710,972 short buns, a large increase in response to the demands of the war, from an average of 400,000 tons in the years immediately before the war.
Canada and Mexico are well supplied with reserves of zinc ores and have exported large quantities into the United States in past years. During the early years of the European War large imports of zinc concentrates were brought to the United States from Australia, where the extensive deposits of lead-zinc ores of the Broken Hill lode of New South Wales have been for years the main foreign dependence of the zinc smelters of Belgium. Germany and France. The zinc deposits of Rhodesia Broken Hill in Africa are extensive, and there are many deposits in Algeria and Tunis. The Bawdwin deposits of India are reckoned the largest in the world, as are also those of the Riddcr and adjoining concessions in the Irtysh region of southwestern Siberia. The chief zinc-producing regions of Europe are the Upper Silesia district, formerly a part of Prussia; the Rhine district of Germany; the island of Sardinia in Italy, and the Santander and Cartagena districts of Spain.
Before the complex ores, sulphides of sine, lead, copper and other metals — the refractory ores of the metallurgist —are treated in the usual practice by smelting in the blast furnace, the zinc minerals must be separated from the others because zinc interferes so greatly with the reduction of the other minerals that a •fine' or 'penalty" is placed by the smelter on ores containing zinc above a fixed limit, de pending on circumstances. Moreover, the zinc is lost. Hence practically all zinc-bearing ores are subjected to milling, in which the zinc minerals arc separated from the others and all arc concentrated to workable richness. In the Joplin region ore of lower metallic content than anywhere else in the world is profitably mined. In one type of deposits, the 'sheet ground.' the ore mined in 1916-17 averaged 1.3 per cent of zinc and 0.3 per cent of lead, as metal content of the con centrates. e zinc concentrates average from 58 to 59 per cent of zinc. In the Broken Hill district of New South Wales in early years the zinc u as separated as middlings and accumu lated in huge stacks. By the flotation process, perfected in that region since 1903. the sulphide mineral., are floated off in a froth while the gangue minerals sink to the lottom. The stocks of :nicky middlings thus became avail able and have furnished the bulk of Broken Hill's large annual output of zinc concentrates in recent years. The flotation process has likewise made available large reserves of lead-zinc ores preciously unworkable in various parts of the world.