284 Mr. J. A. Wanklyn on the Doctrine of 



thing is observable ; for there exists a compound containing the 

 very positive potassium linked with the very positive ethyle. 



It is not from the side of the electro-chemical theory that the 

 prohibitory statutes have issued, but from the theory of uniform 

 and constant saturation. This theory, which is now taking a 

 very definite form, and which appears to be the highest generali- 

 zation yet attained to in chemistry, has been drifted into, as it 

 were, during the last ten years. Its nature may be explained as 

 follows. Every atom of which matter is composed has a con- 

 stant and invariable capacity of saturation (which differs accord- 

 ing to the kind of matter) ; and in whatever form of combina- 

 tion the atom happens to be placed, it is always in a state of 

 perfect saturation. Impossible forms of combination are obvi- 

 ously forms in which atoms are represented as not saturated. 



Sometimes the atom is saturated with atoms unlike itself, and 

 sometimes it is saturated with atoms like itself. The saturation 

 by a similar kind of atom may be complete or partial; but when 

 partial, the deficiency must be made up by the presence of other 

 atoms. When two or more similar atoms effect a partial saturation 

 of one another, there results a kind of compound atom — incapable 

 of isolated existence, and requiring the presence of a suitable 

 number of atoms. Complications of structure are produced by 

 partial saturations of this kind. The most complete exemplifi- 

 cation of the theory is afforded by the hydrocarbons. The atom 

 of carbon requires four atoms of hydrogen to saturate it. There 

 is only one hydrocarbon known whose structure offers only one 

 atom of carbon in union with hydrogen. This hydrocarbon is 

 marsh-gas, CH 4 . There are multitudes of hydrocarbons besides, 

 but all of them contain carbon-atoms more or less saturated by 

 carbon-atoms ; all of them have a greater condensation of carbon 

 than marsh -gas. 



If one atom of carbon be partially saturated by a second atom 

 of carbon, there result complex groups which require either six, 

 four, or two atoms of hydrogen for their saturation. Thus two 

 detached atoms of carbon would take eight atoms of hydrogen 

 and produce two independent chemical structures. If the two 

 atoms of carbon enter into combination to the least possible 

 degree, two atoms of hydrogen must be set free ; if they com- 

 bine doubly with one another, then four atoms of hydrogen 

 must be evolved ; if triply, then six of hydrogen must go ; and 

 if they perform a total saturation, all eight atoms of hydrogen 

 must leave. 



Now, as a matter of experiment, the labours of chemists have 

 produced three and only three hydrocarbons which contain, in 

 the same volume of gas, only twice as much carbon as is pre- 

 sent in marsh- gas. They are C 2 H 6 , hydride of ethyle; C 2 H 4 , 



