.J68 ■ REPORT— 1902. 



cyanides, and the vest, are both numerous and well defined. "Whatever other view 

 ■we shall have to take ol" the constitution of Gomberg's remarkable ' triphenyl- 

 methyl,' it will certainly not be that it is identical with the radical of the tri- 

 phenylchlormethane from which it is derived, unless we are prepared to allow 

 that carbon is sometimes tervalent. Ethylene the substance diners from ethylene 

 the radical in having its two carbons differently related ; but it is difficult to 

 see how to make a similar distinction in the case of Gomberg's substance. 



In those other cases in which the point is not strictly determinablh-, only because 

 the resulting substances are the simple substances themselves, it required but the 

 recognition of molecular quantities to make it evident that these cases run 

 parallel with the others. For, in all changes which can be satisfactorily followed 

 out, the resulting or entering quantity of the simple substance is twice as great as 

 that which can have come from, or gone to form the molecule of either of the 

 compound substances. But if, so far as can be traced, a simple substance comes 

 only half from one molecule of any of its compound^, none of these compounds can 

 contain or be composed of simple substances. All simple substances, therefore, 

 as well as all compound substances, enter into and come out from chemical 

 changes as dual in all of them in origin and disappearance. Their colligative 

 properties have been appealed to in order to confirm this observation, but with 

 conflicting results, sometimes confirmatory of the chemical evidence, sometimes con- 

 tradictory of it, and sometimes too complex for confident chemical interpretation. 



I refer here more especially to Avogadro's proposition, which is in efi'ect that 

 equal volumes of gases are chemically equal or molecular. As in the case of 

 Dalton's atomic theory, there is to be distinguished in this proposition what 

 Avogadro really put forward as new from what he took for granted. Admitting, 

 as was to him a matter of course, that gases have in equal volumes equal numbers 

 of particles, he asserted that in the case of elementary substances these particles 

 are not the atomic particles, but, as in the case of compound substances, particles 

 compounded of these, which interact with the particles of other gases as chemically 

 equal each to each. If now this proposition is divested of all hypothesis, all 

 reference to the mechanical structure of gases, it becomes the law that equal 

 volumes of gases at the same temperature and pressure, whetlier simple or com- 

 pound, are almost exactly chemically equal quantities, and once in possession 

 of this law we find nothing becomes clearer by assuming that equal volumes of 

 different gases contain the same number of chemically equal particles. This law 

 is, obviously, an advance upon Gay-Lussac's law similar to that of the chemical 

 molecular theory upon the atomic theory of Dalton. Unfortunately, however, it 

 does not hold good in the case of not a few simple substances, and it seems impos- 

 sible from the chemical point of view, and consistently with the molecular theory, 

 to admit that, because the gas-volume has only half the expected mass, the 

 chemical molecule of sodium or mercury is not bipartite like that of hydrogen or 

 oxygen, and chemically equal to either. 



The dual constitution or chemically compound nature of the simple substances 

 as thus established by the part they take in chemical interactions furnishes further 

 evidence of the untenability of the belief that the molecule is clieniically composed 

 of two substances, or their substitutes, simpler than itself, when we consider that, 

 were this true, then; would be chemical union between two things perfectly alike, 

 two portions of the same thing. This diHiculty was, I believe, first raised by Berze- 

 lius, and has never been met. Physically, the matter is simple enough, if motion in 

 the opposite direction is not counted as a difference betwen two masses. But this 

 would be a non-elective union, whilst chemical union is elective. 



The difficulty, insurmountable when made, does not arise when the fact is 

 recognised that every chemically single substance, w'hether simple or compound, 

 is, as a substance, one and without parts, and can never, therefore, be built up of 

 or broken down into parts different from itself. One substance (as two molecules) 

 or two substances change into two others or into two molecules of one, in an 

 interaction which is instant, uninterrupted, and irresolvable into stages, where the 

 interaction is .single in character. But just as a body can be mentally analysed 

 fts in the investigations of dynamics) into mass and motion, which apart are un» 



