SOAP, Medical Uses of. In pharmacy and medicine the term soap is applied to combinations not only of oily and fatty matters with, the alkalies soda or potash, but also with the volatile alkali (ammonia), lime (an alkaline earth), and metallic oxides, especially oxide of lead ; like wise to solutions of resins in liquid potash, such as guaiacin [GLAIA c:rir], called therefore Sapo guaiacintis. The combinations of oils with ammonia or lime, being very thin, are generally termed liniments; the common one of hartshorn with oil is an example of the former, while oil and lime-water constitute the common application to burns termed Carron oil, from its frequent employment in the great iron-works at that place. The combination of oil with oxide of lead is generally termed a plaster. Some combinations of a volatile or fixed oil with an acid are sometimes called soaps, such as that of oil of turpentine with hydro chloric acid (artificial camphor), or of almond oil with sulphuric acid (Sapo aeidus) : but these are scarcely entitled to be so regarded. Among continental pharmaceutists, many cerates and mixtures of metallic salts with common soap are termed soaps, but they are more correctly called plasters.
Of hard soaps, the fine kinds are made with soda and the purer vegetable oils, and the inferior kinds with animal oils or the coarser vegetable oils or resins. White soda soap is prepared with caustic soda and olive oil (in Spain) or with almond oil (in France). In its purest state it is called medicinal soap ; in a lees pure state, it is called Alicant, Venice, or Spanish soap. The Castile or marbled soap has this appearance communicated to it by sulphate of iron and red oxide of iron being added and stirred through it when the soap is nearly made. , These are impurities which render it less fit for medical use in many cases ' than the white soap. When properly prepared, white soap should neither make an oily mark on paper nor have a burning alkaline taste. It
should be perfectly soluble in pure water and in alcohol. [Soes-Tesr.] When an alcoholic solution is evaporated, the residuum constitutes transparent soap.
White soda soap is the only one which should be used internally. It is chiefly employed to form pills, which are gently aperient and antacid ; their power in this latter respect is greatly increased by the addition of exaiccated carbonate of soda : this combination is of great utility in the treatment of gouty and calculous disorders, when an alkali is indicated. In other cases it Is used to prevent the pill', becoming bard and insoluble ; such as compound rhubarb pills. White soap furnishes a ready antidote to the strong mineral acids, in cases of poisoning by any of these.
Soft soap is directed by the London Pharmacopeeia to be made with potash and olive oil only, but this order is seldom complied with. The soft soap, in which both soda and potash are used, is made with olive and ether oils and tallow. It is employed euly to form the compound sulphur ointment. Soft soap is of great service in many cutaneous diseases, several of which, when in a mild form, may be cured by it alone. It may be rendered still more useful by the addition of sulphur or sulphuret of potash (liver of sulphur). In the treatment of scabies, porrigo (ring-worm), and such diseases, this application is far superior to the ointments and other greasy compounds commonly employed, which increase the filth or uncleanness by which the disease is aggra vated. It is also much cheaper. Many other soaps are vended, pretending to special qualities, such as glycerine soap, tar soap, &c. Soap formed of cocoa-nut oil has the great advantage of being soluble in salt water, and so can be used at sea.