Chromic Acid

( Chem.) This acid occurs in nature in combination with lead as chrome-yellow, and with iron as chrome iron-ore. It is prepared by adding one measure of a warm saturated solution of bichromate of potash to one and a half of concentrated sulphuric acid. The acid is added in small portions at a time, the solution being allowed to cool between each addition. Chromic acid crystallizes out, and bisulphate of potash remains in solution. The crystals of chromic acid must be removed with a platinum knife, and set to drain in a funnel stopped with asbestos. They must not be heated or brought into contact with organic substances. As soon as the best part of the sulphuric acid has drained away, the crystals are di olved again and re-crystallized under the air-pump. Chromic acid crystallizes in fine red needles, which are very deliquescent, and soluble in water. Although chromic acid is one of the most powerful oxidizing agents known, it is easily decomposed by light and organic substances. When absolute alcohol is poured on crystals of chromic acid, the former is oxidized with sufficient energy to cause combustion, the chromic acid being reduced to sesquioxide of chromium. Sugar and other organic substances have the same power of decomposing chromic acid. Chromic acid bears great analogy to sulphuric acid. Both these acids are isomorphous; they are both monobasic, and they form an acid and a neutral salt. The most useful of these compounds of chromic acid is the bichromate of potash, which forms fine red tubular crystals, which are anhydrous, and remain unchanged by exposure to the air. Bichromate of potash di olves in ten parts of cold water, the solution having a fine red color and an acid reaction. The chromate is easily formed from the bi