TRAXSACTIDNS OF SECTION P.. 0G9 



known, and as tliesc auain can eacli be conceived of as furtlier divided, resolved, 

 condensed, and otherwise Cjualitied as centres of mass, compounded motions, and 

 60 I'ortli, so the chemist is enabled mentally to find quantitatively defined this, 

 that, and the other mark of the many chemical interactions which have or may 

 have gone to bring it into existence, and will or may again have place in the 

 possible forms of its dissolution into others. The two methyls in the constitution 

 of ethane, about which we are quite certain, are not two things held together till 

 some interaction sunders them in the chemical dissolution of ethane, but the 

 double mark of similarity between it and other methyl compounds in their chemi- 

 cal interactions. We cannot say that only one part of the ethane is methyl, or 

 hydrogen, or carbon, but that part of its nature, of its constitution, is its behaviour 

 as a methyl compound, or, again, as an ethyl compound ; or, more comprehensively 

 but less specifically, part of its constitution is its beliaviour as a hydrocarbon, as a 

 hydrogen and as a carbon compound. But these are different aspects of it, 

 different relations of it, not differing parts of the one homogeneous substance. 



With the laudable object of combating the prevalent notion tliat matter is 

 something which is the basis or essence of a body, something acting as the medium 

 of the manii'estation of its forms of energy, a distinguished and most lucid writer 

 on chemistry has, adequately perhaps for that object, represented a body as a 

 compound of the various forms of energy subsisting together and cohering in cer- 

 tain proportions within the volume of the body. Jiut this presentation of a subject 

 HS a cohesion or association of forms of energy is on the same footing as the pre- 

 sentation of ethane as consisting of two methyls bonded together, or two portions 

 of carbon with six of hydrogen. It is compounding what cannot be had apart, 

 what cannot be even conceived of as separate, so far as bodies are concerned. The 

 analysis of bodies into manifestations of different properties are only mental opera- 

 tions. A moving body, a hot body, a green body, an explosive body, becomes by 

 legitimate abstraction u phenomenon of motion, of heat, of colour, or of light, or 

 a chemical phenomenon as our needs require ; but the body is there all the while, 

 and its undivided and continuous existence is indispensable to the phenomenon. 

 The body can be hotter or colder, but not that only, — not that without other differ- 

 ences ; red-hot iron is throughout a very different thing from cold iron, and ice 

 differs widely from steam in most of its properties. A substance is no more com- 

 posed of its properties or energies than it is composed of its so-called elements. 

 It manifests its presence in a thousand and one ways more or less distinguishable ; 

 its properties are so to manifest itself. But no divisibility of itself while it remains 

 itself can be thought of, no differentiation can be suggested, no nucleus with its 

 superinduced properties can be traced. 



It ought, therefore, to be possible to express all the particulars of chemical 

 constitution without making any assumption as to substances having parts or 

 structure. Of chemical constitution itself, I doubt whether there is to be found a 

 definition which is not couched in language having reference to the minute 

 mechanical structure of substances, notwithstanding the fact that all knowledge of 

 their chemical constitution has come to us through observation of the properties of 

 the substances themselves, and more particularly their relations in cases of double 

 decomposition. Bearing in mind that .ill terms are relative, I think the chemical 

 constitution of a substance may be defined as the resemblances shown by it in its 

 chemical changes to other substances, often better known than it and' taken as 

 types, these resemblances being indicated and described usually by means of 

 special nomenclature and notation. As this nomenclature and notation have been 

 developed out of those designed to express chemical composition, it is well to 

 point out that the notion of chemical constitution is independent of that of the 

 latter, though clothed to some extent in its language and symbols. 



The notions of radical and atom are so intimately related as to be often used 

 indifferently, the one for the other. The radical, ethylene, is always an atom of 

 ethylene, the radical nitrogen always an atom of nitrogen. Eadical and atom 

 are in fact tho qualitative and quantitative aspects of the same thing. They 

 are thus exactly parallel with substance and molecule. We can think of 

 unquantified substance, and perhaps of imquantified radical, but in chemistry vcq 



