ORaANIC MATTER. 9 



plays in organic actions, we shall see the significance of this 

 extreme readiness shown by its compounds to undergo 

 change. Eeturning from these facts parentlietically 



introduced, we have next to note that though among these 

 binary compounds of the four chief organic elements, there 

 are a few active ones, yet the majority of them display a 

 smaller degree of chemical energy than the average of binary 

 compounds. Water is the most neutral of bodies : usually pro- 

 ducing little chemical alteration in the substances with which 

 it combines ; and being expelled from most of its combinations 

 by a moderate heat. Carbonic acid is a relatively feeble acid : 

 the carbonates being decomposed by the majority of other acids 

 and by ignition. The various hydro-carbons are but narrow 

 in the range of their comparatively weak afiinities. The 

 compounds formed by ammonia have not much stability : they 

 are readily destroyed by heat, and by the other alkalies. 

 The affinities of cyanogen are tolerably strong ; though they 

 yield to those of the chief acids. Of the several oxides of ni- 

 trogen it is to be remarked, that while those containing the 

 smaller proportions of oxygen are chemically inert, that con- 

 taining the greatest proportion of oxygen (nitric acid) though 

 chemically active, in consequence of the readiness with which 

 one part of it gives up its oxygen to oxidize a base with 

 which the rest combines, is nevertheless driven from all its 

 combinations by a red heat. 



These binary compounds, like their elements, are to a con- 

 siderable degree characterized by the prevalence among 

 them of allotropism ; or, as it is more usually called when 

 displayed by compound bodies — isomerism. Professor Graham 

 finds reason for thinking that a change in atomic arrange- 

 ment of this nature, takes place in water, at or near the 

 melting point of ice. The relation between cyanogen and 

 paracyanogen is, as we saw, an isomeric one. In the above- 

 named series of hydro-carbons, differing from each other only 

 in the multiples in which the elements are united, we find 

 isomerism becoming what is distinguished as polymerism. 

 2 



