Prep. Made by burning sulphur with a little nitre in leaden chambers, the sulphurous acid fumes coining in contact with nitrous acid and watery vapour, cause the higher oxidation of the sulphur, and the formation of sulphuric acid; if sulphur is burnt without nitre, sulphurous acid is produced. The sulphuric acid of commerce, when free from arsenic, is directed in the Pharmacopoeia to be purified by distilling it with a small quantity of sulphate of ammonia, by which means any nitrous acid is decomposed and got rid of.
Prop. & Comp. Sulphuric acid is an oily-looking colourless liquid; sp. gr. 1.846; [1.843. U. S.] having no odour, but an intensely burning acid taste, chars most vegetable substances and becomes darkened, absorbs water rapidly, and when mixed with it evolves great heat. Composition (HO, So3). An anhydrous acid (So3) can be made. Diluted with an equal measure of water it generally gives a slight white precipitate of sulphate of lead (derived from the leaden chambers), which is held in solution by the strong acid; when diluted with water it gives a copious precipitate with chloride of barium. Diluted with 12 parts of water, it should give no yellow precipitate with sulphuretted hydrogen, indicating the absence of arsenic, etc. One fluid drachm requires for neutralization 206 measures of the volumetric solution of soda. It leaves no residue when evaporated in a platinum crucible. When a solution of sulphate of iron is poured upon oil of vitriol, no purple ring is formed at the surface of the two solutions; this shows the absence of nitrous acid.
Off. Prep. Acidum Sulphuricum Aromaticum. Aromatic Sulphuric Acid. (Sulphuric acid, three fluid ounces; rectified spirit, a sufficiency to make forty fluid ounces; cinnamon, in coarse powder, two ounces; ginger, in coarse powder, one ounce and a quarter. Prepared by maceration and digestion.) Sp. gr. 0.935. Six fluid drachms require for neutralization 84.75 measures of the volumetric solution of soda. [U. S. Sulphuric acid, six troy ounces; ginger, in coarse powder, a troy ounce; cinnamon, in coarse powder, a troy ounce and a half; alcohol, a sufficient quantity; add the acid gradually to a pint of alcohol and allow the liquid to cool; mix the ginger and cinnamon, and, having put them into a percolator, pour alcohol gradually upon them until a pint of tincture is obtained; lastly, mix the diluted acid and the tincture.]