This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Is found in the animal kingdom, in the gastric juice of mammals and fishes; in the vegetable kingdom (Isatis tinctoria); in the mineral kingdom combined with metals, earths, and alkalies (sodium chloride, etc.), and in the springs of volcanic regions. The hydrochloric or muriatic acid of the Pharmacopoeia is a solution of hydrochloric acid gas in water, to the extent of nearly 32 per cent. by weight.
Being a volatile acid, it can be prepared from any chloride by distillation with the less volatile sulphuric acid - common salt is usually employed, and hence the acid has been termed "spirit of salt," and "marine acid." When salt is mixed with dilute sulphuric acid, sulphate of sodium is formed, and free hydrochloric acid distils over into a receiver containing water, in which it is very soluble.
NaCl + H1SO4= NaHSO4 + HC1.
The pure acid is colorless, but the commercial acid yellowish, owing to the presence of some organic matter, as cork, or of ferric chloride, from the iron stills in which it is prepared. It has a very sour taste and a suffocating odor, giving off white fumes when exposed to the air, from escape of the acid gas, and its union with the moisture of the atmosphere. A rod dipped in liquor ammoniae and held over a bottle of the acid forms dense white fumes of sal ammoniac; nitrate of silver produces a curdy white precipitate of chloride of silver, insoluble in nitric acid, soluble in ammonia, and becoming dark on exposure to light. The sp. gr. of the acid varies with its strength, the strongest having a density of 1.21. The application of heat should dissipate it without residue, implying the absence of lead and solid impurities. It may contain sulphurous acid, which would be detected by action on lead-paper.
The mineral acids in moderately strong solution may be absorbed through the skin, as proved, for instance, by the physiological effects produced by the nitro-muriatic bath. Dilute hydrochloric acid, taken internally, is absorbed by the stomach, probably unchanged, but any that passes into the intestines would have time to combine in part with soda, and form chloride of sodium before entering the capillaries. It has been said that any acid introduced as such into the blood becomes so closely combined with the albumen as to reach the emunctories before being wholly combined with alkali, but if so, the acid is not traceable by test paper (F. Walter: "Die Wirkung der Sauren, etc.," Archiv. fur Exper. Pathol., April, 1877). According to this careful observer an acid reaction of the blood is incompatible with life. Elimination is effected mainly by the urine, the quantity and the acidity of this excretion being usually increased.
Strong hydrochloric, like other mineral acids, acts with energy on animal tissue, abstracting water, and combining with potash, soda, and lime bases: it does not penetrate so deeply as sulphuric or nitric acid, but produces a white stain, and this part afterward sloughs. On the digestive tract, strong doses have a similar action, and excite gastro-enteritis. Fermentation of any kind is arrested by this acid. Dr. John Dougall considers it, when diluted with twenty parts of water, "the cheapest, most easily used, and most effective non-aerial disinfectant," especially for typhoid excreta and the bed and body-clothes of persons with infectious disease (British Medical Journal, ii., 1879).