Lond. Edin. Acidum sulphuricum venale. Dub. Sulphuric acid. (Specific gravity, 1.850. Lond. Dub. 1.845. Edin.)

Syn. Acide sulphurique (F.), Vitrioliil schwefelsaiire (G.), Acido solforico (7.), Vitriool oli.-Reines Zwavebzuur (Dutch), Vitriol olje (Dan.), Vitriolja, Swafwelsyra ( Swed.), Gundaica Atr. (H.), Gundudaek Travagum ( Tarn.), Arck-gowgird (Pers.), Rooch (Arab.).

This acid is said to be found, in a concrete state, in the cavities of some volcanic mountains, and dissolved in some mineral waters1; but, for the purpose of medicine and the arts, it is prepared artificially, either by decomposing sulphate of iron 2 by the process of distillation in close vessels, or by the combustion of sulphur. The first mode is the most ancient, and is still employed in several places on the Continent; but the second is that generally adopted by the manufacturers in Great Britain, and therefore requires particularly to be described.

Into a chamber lined with sheet-lead, having no opening but a small door placed a few inches from the floor, and made to shut very close, water is poured so as to cover the floor, and rise upon it to the height of one or two inches. A mixture of eight parts of refined Sicilian sulphur and one of nitre is burned on a furnace, in such a manner that the vapour is conducted into the leaden chamber.3 The nitric acid of the nitrate yields oxygen to the sulphur, and converts a portion of it into sulphuric acid, which combines with the potassa of the nitrate; but the greater part of the sulphur in vapour uniting with the oxygen of the air of the chamber is formed into sulphurous acid gas, whilst nitrous acid results from the decomposition of the nitric acid: these uniting, aided by humidity, lose their gaseous character, and form a white crystalline compound, which coming in contact with the water below, the sulphurous acid is changed into sulphuric acid at the expense of the nitrous acid, which, being thus robbed of its oxygen, escapes in the form of binoxide of nitrogen.

This gas, now rising to the roof of the chamber, towards the aperture, attracts a fresh supply of oxygen, and becomes again nitrous acid, which descending, owing to its density, among the sulphurous acid gas, once more converts it into sulphuric acid, and is again disengaged when it comes in contact with the water, to undergo fresh combinations and decompositions, which go on successively until the whole of the sulphurous acid is changed into sulphuric acid.1 When the water is sufficiently acidified it is drawn off through a leaden pipe, with a stop-cock, at the bottom of the chamber; and contains, besides sulphuric acid, some sulphurous acid, a portion of nitric oxide, and some sulphate of lead. The liquor is at first of a brownish colour; but after it is concentrated and purified, first by evaporation in leaden boilers and afterwards by boiling in large green glass retorts, it becomes a colourless, dense fluid, having, when perfectly pure, a specific gravity not exceeding 1.8485 : and is brought to market in large globular glass bottles, surrounded with wicker-work, and sold under the name of oil of vitriol.

1 Hence the old names, oil of vitriol and vitriolic acid, which are still the commercial names of this acid, from green vitriol, the old name of the sulphate of iron. This method is still practised at Nordhausen in Germany. The acid is disengaged from the oxide of iron by the heat; but, owing to the small quantity of water which it contains, it is of greater specific gravity and more fuming than the acid which is manufactured in this country. The specific gravity of the fuming acid of Nordhausen is 1896.

2 M. Baldassari stated that he had found it, in 1776, crystallized in a grotto of Mount Amiata: M. Pictet saw it dropping from the roof of a grotto near the town of Aix in Provence: M. Humboldt found it mixed with hydrochloric acid in the waters of the Rio-Vinaigre; and Vauquelin detected it in the water of a lake in the island of Java.

3 This process was first used by Dr. Roebuck in 1749. Edin. Phil. Trans. vol. iv.

Sulphuric acid thus prepared is not perfectly pure, but is united with about three or four per cent, of saline matter, which consists of two thirds of sulphate of potassa, and one third of sulphate of lead, derived from the chambers in which it is manufactured. Both these impurities are precipitated by adding three parts of distilled water to the acid, which can again be concentrated by distillation; thence the addition of water is a good test of the purity of this acid. The lead is thrown down in the form of a white insoluble powder; from which the pure acid can be decanted. The amount of these impurities may be readily ascertained by evaporating a definite weight of the acid in a platinum cup, placed on the red cinders of a common fire.2 It is sometimes adulterated with sulphate of potassa, for the purpose of increasing its specific gravity; in which case the best method of detection is to saturate the suspected acid with ammonia, and then to expel the sulphate of ammonia thus formed by a red heat: the sulphate of potassa with which the acid was adulterated will remain fixed.

According to Dr. Ure, the pure liquid acid, which is, accurately speaking, a hydroacid of sp. gr. 1.7245, consists of about 81.54 parts of real acid, and 18.40 of water; and the elements of the real acid, according to the estimate of Dr. Thomson1, which is probably the most accurate on this subject, are 40 of sulphur, and 60 of oxygen, in 100 parts of acid; or one atom of sulphur = 16.1, and three atoms of oxygen, 8 x 3 - 24; but with regard to these proportions chymists are not agreed.2 The equivalent of this acid is 40.1.

1 A white saline matter is often deposited on the sides of the leaden chambers. Dr. Thomas Thomson analyzed this, and found it to consist of sulphurous acid, sulphuric acid, nitric acid, sulphate of lead and water. Records of General

Science, vol. iv. p. 96.

2 Dr. Ure, who suggested this test, says, "If more than 5 grains of matter remain from 500 of acid, we may pronounce it sophisticated." Journal of Science the Arts, vol. iv. p. 115.

Qualities.-Liquid sulphuric acid, when pure, is as colourless and transparent as water 3, inodorous, corrosive, heavy; and has the consistence of oil: its specific gravity at a temperature of 60°; Fahr. is 1.845, and one fluid ounce weighs fourteen drachms. It has all the generic characters of an acid; reddening the vegetable blue colours when diluted with a sufficiency of water; but when undiluted, as it carbonizes all vegetable and animal matters, it turns vegetable colours brown. Even when largely diluted, it has an intensely acid taste. When rubbed between the fingers, it feels at first unctuous, owing to its attracting moisture, and dissolving the cuticle; but it afterwards excites a burning sensation. It freezes at 15° into six-sided prismatic crystals 4, bevelled at both extremities: when of the specific gravity of 1.845, it boils at 650°; and at a higher temperature, it is decomposed and converted into sulphurous acid and oxygen gas. It attracts water so rapidly from the atmosphere, as to increase its weight one third in twenty-four hours, and to double its weight in the course of a month (hence the necessity of keeping the air excluded from it), and at the moment it unites with water, the temperature of the mixture is much raised: this rises to 300°, when four parts by weight of the acid are suddenly mixed with one of water.

It acquires a brown colour when mixed with any vegetable matter5, and converts syrup into charcoal; therefore bottles in which it is kept must be stopped with glass stoppers. When brought to sp. gr. of 1.780, by being diluted with water, it boils at 435°, and freezes at 45°, or 13 degrees above the freezing point of water; a fact important to trading chymists, as in this state it is apt to burst the bottles in which it is kept, by its expansion in the act of freezing.6 It forms neutral salts termed sulphates, with the alkalies, earths, and metallic oxides; separates the acids of all other salts, and decomposes the alkaline and earthy sulphurets. The strength of this acid is readily determined by saturating it with dry carbonate of soda, 53.3 grains of which indicate 40.1 of real acid. An unerring test of the presence of this acid is a solution of chloride of barium. It precipitates all astringent infusions.

1 System of Chym. 5th ed. vol. i. p. 288.

2 Bucholz makes the proportions to be 57.5 of sulphur, and 42.5 of oxygen.

3 Sulphuric acid is so easily coloured by contact with either vegetable or animal matters, without being deteriorated, that we cannot regard the slight colour which it acquires from these circumstances as any indication of its impurity.

4 Macnab, Hudson's Bay.

5 This is owing to its strong affinity for water, breaking the affinities which exist between the vegetable components, so as to occasion the hydrogen and oxygen to unite and form water, while the carbon is precipitated.

6 See Parke's Chymical Essays, vol. ii.

Medical properties and uses.-This acid is a valuable tonic astringent; but, as it is employed internally in a diluted state only, its medicinal powers shall be explained under the article Acidum Sulphuricum Dilutum. Although it powerfully corrodes the skin, yet, on account of its fluidity, it cannot be used as an escharotic; but when united with sixteen times its weight of lard, it forms an ointment which has been successfully employed in the cure of scabies. It is a strong corrosive poison. When it has been taken into the stomach, either accidentally or as a poison, it produces the following symptoms : excruciating pain in the stomach and bowels, faintings, feeble pulse, frequent trismus, difficult deglutition, vomitings, convulsions, and death. The tongue, uvula, tonsils, insides of the cheeks, and fauces, appear of a yellowish white colour, and wrinkled, the teeth are surrounded by a black circle, and the lips are yellowish. What is vomited, effervesces with chalk and marble, and corrodes leather. It most frequently proves fatal without entering the stomach, by its corrosive action on the oesophagus.

The best antidote is magnesia and water.1

Officinal preparations.-Acidum sulphuricum purum, D. Acidum sulphuricum dilutum, L. E. D. Acid, sulphuricum aromaticum, E. D. Sulphas potassae, L. E. D. Potassae bisulplias, L. D. Sodae sulphas, L. E. D. Magnesiae sulphas, L. E. D. Ferri sulphas, L. E. D. Hydrargyri chloridum,L. Hydrargyri bichloridum, L. E. Hydrargyri murias corrosivus, D. Sub-sulphas hydrargyri flavus, E. Zinci sulphas, L. E. D. Unguentum acidi sulphurici, D. Aether sulphuricus, L. E. D.