CARBO-HTDRIDE 



717 



bodies which consist of carbon and hydrogen only. The number of hydrocarbons 

 now known is very great, and the list is increasing every day. They were formerly little 

 understood, but so much has now been done that the anomalies and difficulties 

 attending their history are rapidly disappearing. Although the number of individual 

 bodies is very considerable, they are derived from a few great families. The principal 

 are the following : 



Homologues of Olefiant gas. 



Methyle. 



Marsh gas. 



Benzole. 



Naphthaline. 



Isomers of Turpentine. 



The other families which yield hydrocarbon derivatives are less important than the 

 above, and will not be noticed here. 



It is curious that the destructive distillation of organic matters is, of all operations, 

 the most fruitful source of these bodies. Coal yields a great number, the nature 

 varying with the temperature. When ordinary coals are distilled at very high tem- 

 peratures, as in the production of gas, hydrocarbons belonging to the first four 

 families are produced, and also a considerable quantity of naphthaline ; but when, on 

 the other hand, they are distilled at as low a heat as is compatible with their thorough 

 decomposition, they yield fluid hydrocarbons, principally belonging to the first two 

 classes, accompanied, however, by a considerable quantity of paraffine. The homo- 

 logues of olefiant gas have acquired extreme interest, owing to the brilliant results 

 obtained by MM. Berthelot, and De Luca, by Cahours, and Hofmann in the study 

 of their derivatives. The homologues of methyle have attracted considerable atten- 

 tion, in consequence of the successful isolation, by MM. Frankland and Kolbe, of 

 the singular group of hydrocarbons known as the organic radicals, and which, until 

 then, were regarded as hypothetical bodies, existing only in combination. 



The hydrocarbons homologous with benzole not only exist in considerable quantity 

 in ordinary coal naphtha, but are produced in a great variety of interesting reactions. 

 Those contained in the following Table will show this : 



Table of the Physical Properties of the Benzole Series. 



Benzole has already been sufficiently described, and will not, therefore, be further 

 alluded to. All these hydrocarbons yield a great number of derivatives when 

 treated with various reagents. By first treating them with strong nitric acid, so 

 as to obtain nitre-compounds, that is to say, the original substance in which an 

 equivalent of hydrogen is replaced by hyponitric acid NO 4 (W 2 O 4 ), strongly odorous 

 oils are produced. When treated with sulphide of ammonium or protacetate of iron, 

 these oils become reduced, and yield a very interesting series of volatile organic 

 bases or alkaloids ; these are aniline, toluidine, xylidine, cumidine, and cymidine. 

 Mr. Barlow has shown that special precautions are necessary in converting cymole 

 into nitrocymole, preparatory to the formation of the alkaloid cymidine. Cymole is 

 acted on too violently by nitric acid to allow of the nitro-compound being formed, 

 unless the precaution is taken of cooling the acid and hydrocarbon, by means of a 

 freezing mixture, before allowing them to react on each other. The nitro-compound, 

 when well formed, may be reduced in the ordinary manner. These alkalis have 

 of late years acquired special importance in consequence of the valuable dyes that 

 Mr. Perkins has succeeded in producing from them. See ANILINE. 



Paraffine is a solid hydrocarbon of great interest ; it is found both in wood and 

 coal tar. When coal is distilled for the purpose of producing gas, the temperature is 

 so high as to be unfavourable for its production, and consequently mere traces only 

 are found in ordinary coal-tar. But if any kind of coal be distilled at the lowest 

 possible temperature, not only is the resulting naphtha of much lower density than 

 that produced in the ordinary manner, but considerable quantities of paraffine are 

 found in the distillate. The last-mentioned substance is every day becoming more 



