CHROMIUM (Gr. %$pa "color," in al lusion to the colors exhibited by its compounds), a metallic element discovered in 1797 by Vau quelin, in the native chromate of lead of Si beria, and afterward found combined with iron. The metal itself has never been prepared in large quantities, but it can be obtained by the reduction of the oxide by carbon in the electric furnace. It is also obtained by heating the anhydrous sesquichloride of chromium with zinc, potassium or sodium. In nature it occurs most abundantly as the mineral chromite (FeO.Cr,O,), which is often found as a segre gation in ultrabasic rocks such as peridotite.
Most of the world's supply has come from New Caledonia, Rhodesia, Turkey and Greece. In the United States California leads, though there has been a small output from Wyoming and from Maryland. Chromium is extremely hard, of a grayish-white color and less fusible than platinum. Its chemical symbol is Cr, and its atomic weight is 52.1 if 0=16, and 51.7 if H 1. Its specific gravity is from 6.5 to 6.8 and its specific heat is about 0.1, though the latter constant has not been determined with precision. Once separated from oxygen, it does not readily combine with it again. It oxidizes superficially, however, upon being heated in air, and it decomposes steam at a red heat.
Chromium forms four different oxides, whose formula are respectively Cr0 (chro mium monoxide) • Cr,O, (chromium sesqui oxide) • (chromo-chromic oxide); and Obi, (chromium trioxide). Of these the first two act as bases, each yielding a series of salts with various acids. Those salts that are derived from the monoxide, CrO, are called "chromous° compounds; while those that are derived from the sesquioxide, Cr,O,, are called "chromic' compounds. Chromium sulphate, Cr.(SO4),, forms a series of alums with the sulphates of potassium and ammonium, the ele ment behaving in this respect like aluminum. (See ALUM). Chromo-chromic oxide is not chemically active. Chromium trioxide, CrO.,
dissolves in water with the formation of an acid, _HiCr0., which is called "chromic acid,' and is of great Interest to the chemist. Chromic acid forms a series of definite salts that are known as achromates.* One of the best known of these is chromate of lead, PbCrO,, which is used as a pikcment under the name of °chrome yellow,* and is formed hy precipitating chro mate of potassium by a soluble salt of lead. Potassium bichromate, K,Cr,O,, or KsCrO,Cr0,,, is another extremely important salt of chro mic acid; it is used as a depolarizer in electric batteries, as a bleaching and oxidizing agent and as a convenient starting-point in the manu facture of many of the chromium compounds. It possesses the peculiar property of rendering gelatine insoluble upon exposure to light, and for this reason it is used in various photo graphic processes.
Chromium is used to some extent in the manufacture of steel, as it is found that the addition of less than 1 per cent of chromium materially increases the strength, hardness and elasticity of the product.
In medicine chromic acid and potassium bichromate are used. The acid is employed as a caustic; the bichromate is now rarely em ployed because of its irritant propertiel.
Poisoning by chromium compounds is simi lar to that caused by other metallic poisons. The drinking of battery fluid is the usual mode. There is severe gastro-enteritis, nausea, vomit ing of yellowish bloody matter, diarrhoea, pain, colic, tenesmus, great prostration, muscular cramps, rapid and feeble pulse, bloody urine (perhaps suppression of this secretion), feeble and irregular breathing, with coma or convul sions preceding death. A fatal ending may occur in from 4 to 15 hours. At times this result may be delayed and symptoms referable to degenerative processes in the liver and kid neys appear. Treatment is by prompt and con tinued washing of the stomach. Bismuth sub nitrate is indicated in the after treatment, which is symptomatic.