CARBOLIC ACID, a substance having a formula Glis.OH, possessing feebly acid properties, and occurring chiefly in that part of the distillate from coal-tar which passes over at temperatures between 310° and 440° F., known as the °middle oils° or °carbolic oils.° It is also found in small quantity in the later distillate, between 450° and 520°, known as °creosote oil.° Chemically, carbolic acid has the structure of an alcohol (q.v.), and is an aromatic compound derived from benzene by the substitution of the hydroxyl group, OH, for one of the typical hydrogen atoms. It is also known as phenol, phenyl hydrate or phenyl alcohol.
Carbolic acid is obtained for commercial purposes almost exclusively from gas-tar. The carbolic oil is washed with a solution of caustic soda of a specific gravity 1.075 to 1.100. In quantity the solution is somewhat more than sufficient to extract all the carbolic acid, but not enough to take up all the cresylic acid also. The resulting phenate of soda solution is drawn off and is used to wash another por tion of the oil, when the cresylate of soda is decomposed, and the cresylic acid is replaced by carbolic acid. In this way a solution con sisting almost wholly of carbolate of soda is obtained. This is purified by blowing steam through it, as long as it carries away any oils. The purified phenate of soda is then decom posed by carbonic acid gas and a small quan tity of sulphuric acid, and the carbolic acid set free floats on the surface and is skimmed off. The crude carbolic acid thus obtained contains about 15 per cent of water, and a little cresylic acid. It is purified by distillation and crystal lization. A part remains liquid, and this is sold as liquid carbolic acid, or it is turned back to be worked up again. The drained crystals are treated with concentrated sulphuric acid and potassium bichromate, and redistilled. For medicinal purposes it is again distilled in glass vessels.
Carbolic acid, in the pure state, crystallizes in white, deliquescent needles, having a strong characteristic smell slightly suggestive of tar. The reddish color noted when it has been ex posed to the air is attributed to minute traces of lead. It melts at 106° F., and boils, under ordinary atmospheric pressure, at about F. Its specific gravity is about 1.07. It dissolves in alcohol, ether and many other organic liquids, but is only moderately soluble in water under ordinary atmospheric conditions. It readily absorbs a small quantity water from the air, forming a hydrate which is fluid at temperatures above 63° F. If the liquid so formed is shaken with water, the greater part of the carbolic acid separates out upon stand ing, and the vessel is found to contain an upper layer consisting of water in which a small amount of carbolic acid is dissolved, and a lower layer of carbolic acid in which a little water is dissolved. It does not exhibit very
marked acid properties, but dissolves in the alkalis with the formation of salts called phenates. It does not have a strong affinity for the alkaline bases, however, and from a strong solution of sodium phenate (for example) it may be again separated in the form of an oily liquid by the addition of another acid; the new acid appropriating the base to itself, and setting the carbolic acid free. A solution of carbolic acid, even when very weak, develops a red color when boiled with a solution of mercurous nitrate and nitrous acid. This reaction, which serves for the detection of carbolic acid, is said to be delicate enough to indicate one part of the acid in more than 100,000 parts of water. In the arts large quantities of carbolic acid are used in the manufacture of salicylic acid (q.v), and it is an important source of picric acid and coralline in the dye-making industry. It is consumed in immense quantities in making high explosives after transformation into picric acid.
In medicine, carbolic acid has many uses. It is highly poisonous to living matter, and is used extensively to kill bacteria. In surgery it it used to disinfect wounds, and as an antiseptic dressing in proportions of from Y5-2 parts of acid to 100 of water. It, or some of its derivatives or allies, is used to sterilize instru ments and bed linen, the walls and floors of rooms (by washing) and dejecta. Internally, carbolic acid is used as a bactericide, limiting excessive intestinal putrefaction. It is also an anesthetic, and is at times of service in irri tability of the stomach. When used in too concentrated a solution it is an active caustic, causing a white, painless burn. Alcohol is an excellent antidote. Taken internally in pure form in doses over two to three drops it causes poisoning with a characteristic series of symp toms. There is burning in the mouth, fauces, (esophagus and stomach. The whitish scars of the lips and mouth are characteristic. There is great pain, with vomiting of large quantities of mucus, clamminess of the skin and restricted respiration. There is usually ringing in the ears, headache and vertigo; the urine may be suppressed, reddish or greenish; and death re sults with small, rapid pulse, collapse, and, may be, convulsions. Similar symptoms may de velop slowly in sub-gcute forms of poisoning. The urinary symptoms usually lead to the diagnosis. The treatment of the acute form of poisoning is the free use of gastric lavage, in gestion of alcohol usually in the form of whisky slightly diluted and the use of lime water, and solutions of sulphate of soda or sulphate of magnesia. Symptomatic treatment and careful nursing are necessary for other symptoms.