Therapeutics. Externally the strong acid is a most powerful caustic, rapidly destroying all the tissues with which it comes in contact; internally, when much diluted it acts as a refrigerant, tonic, and astringent. It is used to allay thirst in fever, especially when of a hectic character, to check excessive sweating in phthisis, to diminish passive mucous discharges, and haemorrhages, to improve digestion, and brace up the system in debility. Given for some time it increases the acidity of the urine, and may be employed in phosphatic deposits. It has likewise been found serviceable in some chronic skin diseases connected with a low state of system, as in pompholyx diutinus, etc. Recently it has been much extolled for checking diarrhoea. Externally, oil of vitriol rubbed up with lard is sometimes used as an ointment in very obstinate skin diseases, as in porrigo.
Dose. Of acidum sulphuricum dilutum, 5 min. to 25 min., freely diluted; of acidum sulphuricum aromaticum, 5 min. to 30 min.
Adulteration. Water, indicated by a lower specific gravity. Lead, detected on dilution; arsenic, from the use of impure sulphur in the manufacture; and hydrochloric acid, from impurities in the nitre made use of, are sometimes present. Oil of vitriol often becomes much discoloured from a trace of organic matter, such as wood, cork, etc.
The following tests are given in the British Pharmacopoeia for ascertaining the quality of Sulphuric Acid of Commerce, contained in Appendix (A). Sp. gr. 1.84 to 1.85. When the acid mixed with six times its volume of distilled water is placed in contact with pure zinc, and the hydrogen evolved is ignited as it escapes from the capillary extremity of a glass tube, if a dark stain is formed on a piece of porcelain held low down on the flame, the acid contains arsenic, and is to be rejected. When a solution of sulphate of iron is poured cautiously on the surface of the undiluted acid, if a red tint appears at the surface of contact, the acid contains nitrous acid; and if the acid diluted with water as above becomes turbid, it contains other impurities, and in either case requires purification.