SULPHOCYANIC ACID, or THIOCTANIC ACID, HONS. A powerful organic acid analogous in its composition to the well-known cyanic acid (q.v.), HCNO, from which it differs in contain ing sulphur instead of oxygen. Sulphoeyanutes, i.e. salts of sulphoeyanie acid, may be obtained by the direct action of sulphur on cyanides (i.e. salts of hydrocyanic acid). Thus, potassium sulphoeyanate may be obtained by boiling a solution of potassium cyanide with sulphur. Free sulphoeyanie acid may be prepared by decom posing barium sulphoeyanate with sulphuric acid, and distilling the aqueous acid thus ob tained over warm anhydrous chloride of calcium. The acid is thus obtained in the form of a vola tile liquid with a characteristic pungent odor. Pure sulphocyanic acid may he preserved for sonic time if kept in the cold. At ordinary tem peratures it rapidly polymerizes, forming an amorphous yellow substance. Several of the sulphoeyanates are extensively used as mordants in certain dyeing processes. The principal com mercial source of the salts is found in the manu facture of coal gas. The products formed during the destructive distillation of coal include am monia, cyanogen, a certain amount of ammonium cyanide, and certain compounds of sulphur. In course of the purification of the gas, these by products are brought into contact with moist ferric oxide for the purpose of freeing the gas from deleterious sulphur compounds. The sul phur is thus retained partly in the free state, partly as iron sulphide, and by combination with the ammonium cyanide present yields ammo nium salphoryanate, which may be dissolved out of the reacting mixture with water. Ammonium
sulphocyanate itself may be used for the prepara tion of hydrazine. Usually it is transformed into the sulphoeyanate of copper, from which, in turn, the useful sulphocgunate of barium is obtained by the action of baryta. The sulpho eganate of aluminum, another useful salt of sulphoeyanie acid, may be obtained by the action of aluminum sulphate on the sulphocyanate of barium. Itost of the sulphocyanates are soluble in water. Salphocyanate of mercury may be obtained by the action of mercuric nitrate on the sulphocyanate of ammonium. It decomposes on moderate heating, the resulting mass, ex ternally yellow, but black within, assuming a large size and often a most fantastic shape. This sulphocyanate is the principal ingredient of the well-known toy known as 'Pharaoh's ser pents.' Each serpent consists of a little cone of tinfoil, filled with the salt. On lighting the cone at the apex, there begins to issue from it a thick serpent-like coil, which continues twisting and increasing in length to an extraordinary degree.
Like cyanic acid snlphoeyanie acid nishes a simple example of the phenomenon known as tautomerism. The two constitutional formulas corresponding to the acid, as deduced from a study of its two different series of deriva tives, are as follows: