458 SULPHURETTED HYDROGEN SULPHURIC ACID barrels, and in the rural districts sulphur is often burned in old cider barrels to purify them. Sulphurous acid is extensively used in bleaching straw, woollen, and silken goods, and also isinglass and other articles which would be injured by chlorine. (See BLEACH- ING.) It is a powerful antiseptic, and is now employed to preserve meats. (See PRESERVA- TION OF FOOD, vol. xiii., p. 824.) For its most important use, see SULPHURIC ACID. Sulphu- rous acid is dibasic, forming normal, neutral, and double salts. (See SULPHITES.) The bi- nary compounds of sulphur with the metals, or the sulphides, are, when important, men- tioned in the articles on the respective metals, or under SULPHIDES. One of the principal uses of sulphur is in making gunpowder. (See GUNPOWDER.) Medical Properties and Uses. Sulphur is termed in therapeutics a laxative, diaphoretic, and alterative. It is supposed to be carried into the circulation by the fatty matters in the alimentary canal. That it is discharged by the skin is shown by the fact that silver worn about those who are taking it becomes blackened with a coating of sul- phide. It is used in cutaneous and other dis- eases, both internally and externally, some- times artificially prepared, and sometimes as it exists in " natural springs. (See MINERAL SPRINGS.) It has been successfully employed in diphtheritic croup, given suspended in water, and in sciatica and chronic articular rheuma- tism, applied externally upon dry flannel and bandaged to the limb for several days. The officinal preparations embrace confections, plas- ters, and ointments, and precipitated sulphur or lac sulphuris. This latter preparation is made by boiling sulphur with milk of lime, which forms bisulphide of calcium and hypo- sulphite of lime, from the solutions of both of which the sulphur is precipitated by the action of hydrochloric acid. It has the gen- eral properties of ordinary sublimed sulphur, but is in a state of finer division. SULPHURETTED HYDROGEN. See HYDROSUL- PHURIO ACID. SULPHURIC ACID, the hydrate of sulphuric anhydride, or teroxide of sulphur, SO 3 + H 2 O= H a S0 4 . It may also be regarded as a salt of hydrogen, this element holding the place of a basyle to the radical sulphion, S0 4 . (See SALTS, vol. xiv., pp. 582, 583.) The discovery of sulphuric acid is ascribed to Basil Valentine, a monk of Erfurt in Saxony, about 1440. He obtained it by distilling green vitriol or the sulphate of iron, and as the liquid product had an oily appearance when poured out, it was called oil of vitriol. He also obtained it by burning sulphur under a bell glass containing moisture, calling the product oleum sulpTiu- ris per campanum, or oil of sulphur by the bell. This was the germ of the present pro- cess of manufacture, which consists in pro- ducing sulphurous acid and carrying it to a higher state of oxidation by nitrous and hy- ponitrous acids. The old process of distilla- tion from green vitriol is still employed in some parts of Germany, particularly in the neighborhood of Nordhausen in Prussian Sax- ony, and near Prague in Bohemia. Sulphate of iron, chiefly produced by the oxidation of iron pyrites, first has its water of crystalliza- tion expelled, when it is subjected to a high FIG. 1. Distillation of Nordhausen Acid. red heat in earthen retorts placed in galleries in a furnace, as shown in fig. 1. As soon as the acid begins to distil over, the necks of the retorts are passed into receivers. The product is. a brown oily liquid having a density of about 1-9, and fumes in the air, for which reason it is also called fuming sulphuric acid. Its com- position may be expressed by the formula H 2 S04,S0 3 . When gently heated it breaks up into sulphuric anhydride, SO 3 , and sulphuric acid, H 2 S04. If fuming Nordhausen acid is distilled into a receiver cooled by ice, white fumes will solidify on its sides into white silky needles. This product was formerly called anhydrous sulphuric acid. It does not how- ever possess acid properties like the residue in the retort, but requires to be united with wa- ter to enable it to combine with bases. It is tough and ductile, and can be moulded in the fingers for a short time if they are dry. It has a specific gravity of 1-946 at 55 '4, fumes in the air, and when thrown into water hisses like red-hot iron, and forms sulphuric acid. It melts at 65 and boils at about 95, forming a colorless vapor, which is decomposed in high- ly heated porcelain tubes into two volumes of sulphurous anhydride and oxygen. The com- mon way of preparing sulphuric acid at pres- ent, known as the English process, is to oxi- dize sulphurous acid. It is said to have been introduced by Dr. Roebuck about the middle of the 18th century, but the invention is also
