Page:The American Cyclopædia (1879) Volume III.djvu/779

 CARBOLIC ACID CARBON 769 cmghly 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 gly- cerine, 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 Car- bolic Acid and its Compounds," by A. E. San- som, M. D., London ; also in a pamphlet by Dr. E. R. Squibb of Brooklyn, " On the Phe- nols from Coal Tar." In cases of accidental poisoning, olive oil and castor oil are freely given. Saccharate of lime is also recommend- ed 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 309 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 co- piously evolved. Very similar to carbolic acid are two compounds, often found associated with it, called cresol and xylol, which are em- ployed 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 classof phenomena. The following method of obtaining pure carbolic acid from coal tar is given by Hugo Muller (ZeiUcJirift fiir 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 pos- sible 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 neces- sary to remove this water completely by heat- ing 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 quan- tity of crystallized carbolic acid. Crude car- bolic acid, such as is obtained from tar refine- ries, 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, how- ever, 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 com- monly contains a small quantity of a very disa- greeably smelling sulphur compound (phenyl sulphide), which may be removed by distilla- tion 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, puri- fied by one rectification, be dehydrated with one or two per cent, of anhydrous sulphate of cop- per. The distillate solidifies for the most part at 16 C., especially in contact with solid car- bolic acid. CARBON (Lat. carlo, coal; symbol, C), one of the most common and important substances in nature, occurring in a great variety of forms in the vegetable, animal, and mineral king- doms, in the two first named being by far the most considerable element. The charcoal pre- pared from many substances belonging to these presents it pure ; but the diamond is crystal- lized carbon, contaminated, when colorless, by no foreign admixture. In this form carbon possesses the most brilliant lustre, and a hard- ness unsurpassed, which is represented upon the mineralogical scale by the highest number, 10. (See DIAMOND.) Carbon is remarkable for its allotropic character, presenting itself under various forms while still in a state of purity. Besides those named, graphite may be regarded as one of its forms, the trace of other substances met with in its purest qualities be-