Carbolic Acid (synonymes, carbon oil acid, phenol, phenyl hydrate, phenyl oxyhydrate, phenyl alcohol, phenous acid, phenic acid, phenylic acid, phenylous acid, phenylic alcohol, phenolic acid, phenylated water, spirol, saly-con, coal-tar creosote, and incorrectly creosote and cresylic acid), a chemical substance now largely employed in medicine and the arts. In 1832 Reichenbach discovered among the products of the distillation of beech-wood tar a peculiar body to which, on account of its property of preserving meat from decay, he gave the name of creosote. In 1834 Runge found a similar substance in coal tar, which he named carbolic acid, or carbon oil acid. Immediately there arose a controversy among chemists as to the true constitution of these two bodies. Reichenbach, jealous of his fame, maintained that they were identical; but Laurent in 1841 found carbolic acid to be a different body from creosote, and it was he who introduced the new name of phenol, phenic acid, phenylic hydrate (Gr. , to light), in allusion to the use of coal gas for illuminating purposes. The confusion engendered by these early controversies is still apparent in scientific works, and even Gmelin treats of carbolic acid and creosote as being identical. The difficulties of the case have not been improved by the multiplicity of names which have been given to the compounds. For the sake of accuracy and simplicity, it would have been better if all parties had adhered to Runge's original name of carbolic acid.-Runge wrote in 1834: "Carbolic acid is a colorless, acid, oily stuff, that sinks under water, and possesses great refracting power. Its odor is empyreumatic, taste highly caustic and burning. It has powerful action on the skin, accompanied by a burning sensation, producing a white stain, which afterward becomes red, and the skin peels off. In this respect it resembles creosote, but it differs from creosote in being decidedly acid, in being precipitated by acetate of lead, and in not being acted upon by ammonia and air, but changed by even dilute nitric acid into a red-brown substance; it also precipitates gelatine; all which properties are wanting in creosote.
Carbolic acid precipitates albumen as well as gluten, and protects organic matter from decay; and what is more remarkable, it immediately removes all odor from decaying organic matter, such as meat, when this class of bodies is covered with the liquid acid, and in this property is preferable to chlorine. It is not identical with the principle of smoke, as meat treated with it tastes abominably." In his treatise on elementary chemistry, published in 1847, Runge recommends carbolic acid for the embalming of bodies; he says: " The carbolic acid of coal tar, discovered by me, is preferable for this purpose to sublimate or any other agent; it has extraordinary action on decaying matter; for example, stinking fish become entirely inodorous in carbolic acid, and after being dried are not again subject to putrefaction." Since the early researches of Runge many new facts have been ascertained in reference to the body discovered by him. Carbolic acid crystallizes at ordinary temperatures in long colorless needles, apparently belonging to the trimetric system and having a specific gravity of 1.065. The crystals melt at 105° F., while the liquid boils at 369°. They are deliquescent, smell like wood-tar creosote, require 25 to 30 parts of water for solution, but dissolve in all proportions in alcohol, ether, glycerine, and strong acetic acid.
Much of commercial creosote consists solely of carbolic acid. Compounds of carbolic acid with potash, soda, lime, etc, can be obtained; they are called carbolates, and are quite unstable. It is a volatile substance, and is hence readily diffused through the air. A plumped hide immersed in an aqueous solution of carbolic acid is not tanned, but it is not liable to further putrefaction. India rubber is not attacked by carbolic acid, but colo-phonium, copal, and other resins are easily dissolved by it, and remain sticky on drying, which prevents this property of the acid from being employed in the manufacture of varnish. It is a violent poison to plants and animals, and hence must be handled with care. The cases of death from its incautious use are numerous. Owing to its antiseptic power, carbolic acid is a valuable topical application in many surgical cases attended with offensive purulent or other discharges. It was extensively tried by Crookes as a prophylactic against the spread of the cattle plague.
As it is a volatile substance, it possesses the great advantage of being readily diffused through the air. - Carbolic acid paper, which is much used for packing fresh meats, is prepared by melting five parts of stearine at a gentle heat, then thoroughly incorporating two parts of carbolic acid, and subsequently adding five parts of melted paraffine. When fused it can be applied with a brush. Pieces of card-board paper saturated ' with the acid are employed as antiseptics and insect exterminators. When dissolved in 230 parts of water it is used as a gargle, or in 25 parts for painting the throat, or in 50 parts for a carbolic spray. It may be readily mingled with olive or other oils (1 to 25), or with glycerine, for dressing cuts and sores. A great number of remedial agents and disinfecting compounds have been prepared with carbolic acid, 'a description of which may be found in "The Antiseptic System: a Treatise on Carbolic Acid and its Compounds," by A. E. Sanson!, M. D., London; also in a pamphlet by Dr. E. R. Squibb of Brooklyn, " On the Phenols from Coal Tar." In cases of accidental poisoning, olive oil and castor oil are freely given.
Saccharate of lime is also recommended as a remedy, and while this is preparing a little carbonate of lime can be administered. - Some of the distinguishing differences between carbolic acid and creosote are: An alcoholic solution of carbolic acid is turned brown by an alcoholic solution of ferric chloride; creosote similarly treated yields an emerald green color. Carbolic vapor passed over heated zinc dust is easily reduced to benzole. Carbolic acid boils at 369° F.; creosote readily dries up at 212°. Carbolic acid does not affect a ray of polarized light; creosote bends it to the right. Carbolic acid gives a jelly when shaken with collodion; creosote does not. The substitution products and the colors derived from carbolic acid are also characteristic. - Numerous compounds, some of them of great value in the arts, have been prepared from carbolic acid, which will be described under their respective names; the most important of them is perhaps picric acid. Berthelot has succeeded in preparing carbolic acid from acetylene, by treating the latter with sulphuric acid, making a potash salt with the product, and subsequently fusing with caustic potash, when carbolic acid is copiously evolved.
Very similar to carbolic acid are two compounds, often found associated with it, called cresol and xylol, which are employed in many instances as substitutes for carbolic acid. It is proposed to call this class of remedies azymotics, from their property of preventing and sometimes healing infections or zymotic diseases, i. e., diseases produced by fermentation, according to the germ theory of this class of phenomena. - The following method of obtaining pure carbolic acid from coal tar is given by Hugo Muller (Zeitschrift far Chemie, 1865, p. 270): The aqueous solution obtained by treating coal tar with caustic soda or milk of lime, or a mixture of the two, which contains, besides carbolic acid, certain easily oxidizable substances, and a not inconsiderable quantity of naphthaline, is diluted with water as long as naphthaline is thereby separated, and the liquid, which soon turns dark brown, is exposed" to the air in shallow vessels for several days and frequently stirred. The brown solution is then filtered, the quantity of carbolic acid contained in a given quantity of it is determined, and the proportion of acid required to precipitate the entire amount is calculated therefrom.
If now one sixth to one eighth of this quantity of acid be added to the liquid, with constant stirring, the resinous substances altered by the action of the air are first precipitated, together with larger or smaller quantities of cresol and xylol. A further addition of acid precipitates chiefly cresol, and after a few trials it is generally possible so to adjust the quantity of acid that the third and last precipitation shall yield nearly pure carbolic acid, which crystallizes after a single distillation. As even a small quantity of water prevents its crystallization, it is necessary to remove this water completely by heating the carbolic acid nearly to the boiling point, while a stream of dry air is passed over it. The crystallization may be accelerated by cooling, or by the introduction of a small quantity of crystallized carbolic acid. Crude carbolic acid, such as is obtained from tar refineries, may be conveniently purified by treating it several times in succession with soda ley. The first extracts contain the purer product; the precipitation of the carbolic acid must, however, be preceded by dilution with water and exposure to the air.
A perfectly pure product, remaining colorless when preserved, is obtained only when the substances which turn brown by oxidation have been completely removed by exposure to the air. Carbolic acid commonly contains a small quantity of a very disagreeably smelling sulphur compound (phenyl sulphide), which may be removed by distillation over a small quantity of lead oxide. - For the preparation of crystallized carbolic acid, Bickerdike ("Chemical News," xvi., p. 188) recommends that the commercial product, purified by one rectification, be dehydrated with one or two per cent, of anhydrous sulphate of copper. The distillate solidifies for the most part at 16° C, especially in contact with solid carbolic acid.