718 



CARBOLIC ACID 



important, in consequence of the valuable illuminating properties that have boon 

 found to belong to it. Colourless, inodorous, hard at all moderate temperatures, it 

 forms the most elegant material for candles yet discovered. See PAKAFFINE. 



Modern researches have shown that the hydrocarbons generally are formed on one 

 type viz., hydrogen. Assuming hydrogen in the free state to bo a double molecule, 

 IIH, the hydrocarbons are formed by the substitution of one or two equivalents of a 

 positive or negative radical for one or two of the equivalents of hydrogen ; thus 



methyle, the formula of which (for four volumes) is SjjS 8 , or C'H 6 , is hydrogen in 



which both equivalents are replaced by methyle. Olefiant gas is hydrogen in which 

 one equivalent is replaced by the negative radical acetyle, or vinyle, and so on. 



There is one large class of hydrocarbons the rational formulae for which are not 

 known, and which will probably remain in this condition for some time. We allude 

 to the numerous essential oils isomoric with oil of turpentine. Many of those have 

 almost the same boiling point and precisely the same vapour-density as their type ; 

 but in odour, fluidity, density in the liquid state, and various other minor points, 

 are essentially different. The following Table exhibits some of their physical pro- 

 perties : 



Table of the Physical Properties of some Isomcrs of Oil of Turpentine. 



An inspection of the above Table will show that while, beyond doubt, a great 

 number of essential oils are truly isomeric with turpentine, there are some the con- 

 stitution of which is by no means well established. 



The above account of some of the more prominent hydrocarbons is necessarily 

 brief and imperfect ; partly because the limits of this work preclude the possibility of 

 entering minutely into the details of their history, and partly because many of them 

 are described at greater length in other articles, especially under NAPHTHA.. C.G.W. 



C ARBIN-OXi. A synonym of methyl-alcohol or wood-spirit. 



CARBOLIC ACID, Phenic Acid, Phenol, Phenylic Alcohol, or Hydrate of 

 Phenyl, C 12 H 8 2 (C"H 8 O). The less volatile portion of the fluids produced by 

 distillation of coal-tar contain considerable quantities of this substance. It may be 

 extracted by agitation of the coal-oils (boiling between 300 and 400 P.) with an 

 alkaline solution. The latter, separated from tho undissolved portion, contains the 

 carbolic acid in the state of carbolate of the alkali. On addition of a mineral acid, 

 the phenol is liberated, and rises to the surface in tho form of an oil. To obtain it 

 dry, recourse must be had to digestion with chloride of calcium, followed by a new 

 rectification. If required pure, only that portion must bo received which boils at 

 370. If, instead of extracting the carbolic acid from coal-products boiling between 

 300 and 400, a portion be selected distilling between 400 and 428, and the same 

 treatment as before bo adopted, the acid which passes over between 347 and 349 

 will consist, not of carbolic acid, but of its homologuo, crosylic acid C U H 8 2 (C 7 H 8 O). 

 Commercial carbolic acid is generally very impure. Some specimens do not contain 



