156 ISOMERISM. 



rences they present, as is obvious in the following formulae of 

 four of the best characterized members of this isomeric 

 group : 



Equivalents and combining measure. 



Methylene. . . . C 2 H 2 or 4 volumes. 



Olefiant gas. . . . C 4 H 4 or 4 volumes. 



Gas from oil. . . . C 8 H 8 or 4 volumes. 



Cetene. . . . C 32 H 32 or 4 volumes. 



It thus appears that the atom of cetene contains four times as 

 many atoms of carbon and hydrogen as the atom of the gas 

 from oil, eight times as many as the atom of olefiant gas, and 

 sixteen times as many as the atom of methylene ; while as the 

 atom of all these bodies affords the same measure of vapour or 

 four volumes, they must differ as much in density as they do 

 in the number of their constituent atoms. It is not surprizing, 

 therefore, that they all possess different and peculiar properties. 

 Several groups of bodies might be selected from Table II, at 

 page 134, which have a similar relation to each other, the num- 

 ber of their atoms being different, although their relative pro- 

 portion is the same, such as : 



Oil of lemons. . . . C 10 H 8 

 Oil of turpentine. . . C 20 H 16 

 and, 



Naphthaline. . . . C 20 H 8 



Paranaphthaline. . . C 3a II 12 



A still more remarkable case is presented to us in alcohol, 

 and the ether from wood- spirit, in which there is identity of 

 condensation as well as of composition, with, different equiva- 

 lents. Their vapours have in fact the same specific gravity, 

 and contain under equal volumes, equal quantities of carbon, 

 hydrogen and oxygen. But we know that each of these bodies 

 is composed of two others, alcohol of one atom of olefiant gas, 

 and two atoms of water ; arid the ether of wood-spirit, of one 

 atom of methylene, and one of water, so that their constitution 

 and rational formulae are quite different : 



Alcohol. C 4 H 4 + 2HO 



Ether of wood spirit. . C 2 H 2 +HO 

 In another class of isomeric bodies, the atomic weight may 

 be equal, as well as the elementary composition. A pair be- 

 longing to this class are known, which coincide besides in the 

 specific gravity of their vapours. The composition and atom 



