560 REPORT — 1902. 



and therefore, that chemical interaction is a measure of quantity of unlike sub- 

 stances distinct from and independent of dynamical or mass measurement. 



Dalton indeed, did not express himself in any such terms, his mind being fully 

 nossessed with the ancient and current belief upon which he framed his theory 

 that substances are made up of minute, discrete particles. But it is clear enough 

 that his theory was that of the existence of another order of equality between 

 substances than that of weight. Up to his time, the weight or mass of every 

 ultimate particle of any substance whatever appears to have been assumed to 

 be the same, the atoms being alike in every way. That assumption is still made 

 by many thinkers, chemists among them ; we meet it, for example, in the different 

 forms of the hypothesis that the elements are all, in some way, physically com- 

 ■pounded of a universal and only true element, as in Front's hypothesis. Dalton saw 

 things differently, and recognised that, on the assumption of substances being 

 constituted of particles which never subdivide, weight or mass cannot be the same 

 for every such particle, except in the case of those of any one simple substance. 

 Therefore having given some numbers showing what he believed to be the respec- 

 tive weights of the atoms of several simple substances, taking that of hydrogen as 

 of unit-weio-ht, he proceeded at once to invent symbols for these atoms to indicate, 

 not only their distinctness in kind, but above all things their indivisibility and 

 their equality, properties which the use of their atomic numbers would have 

 inadvertently concealed or even apparently denied, and could never have expressed 

 or connoted. 



It was only in this immediate invention and use of chemical symbols that 

 Dalton's conception found clear expression ; and again it is by the universal adop- 

 tion of such symbols that chemists have shown their real acceptance of the atomic 

 theory even while displaying, not infrequently, their scepticism as to its truth. The 

 replacement by Berzelius of Dalton's marked circles for atomic symbols by letters 

 which should recall the names of the substances was in a way a great improve- 

 ment but it has had the serious consequence of causing chemical symbols to be 

 usually first brought under notice merely as serviceable abbreviations for the names 

 of the elements, and only then described as representing their atomic quantities. 

 Now evidently, what the character used as symbol shall be is, theoretically con- 

 sidered, but a petty detail ; the vitalpointis what the character symbolises, and that 

 is the atom. It does not symbolise the name ; it only indicates that and recalls it. 

 It mav be said indeed to represent the atomic number, since it stands in place of it ; 

 but it is made to do so only in order that we may for the time forget this number 

 and have in mind the integral character of the atom. It is not the 4006 parts 

 of sodium hydroxide and 8097 parts of hydrobromic acid, or approximately twice 

 as much of the latter as of the former ; it is not these gravimetrically expressed 

 interacting quantities that we are to think of when the formul£e NaOH and HBr 

 are before us, as we too often strive to do ; it is not these, from a chemical point 

 of view meaningless numbers of parts, but quantities which are equal in the sense 

 of chemistry, that are expressed as such by these symbolic formulas. The real 

 purpose of chemical formulation is not to abbreviate or replace language, but to 

 facilitate, if not ensure, abstraction from and non-contemplation of gravimetric 



numbers. 



I have just passed from atomic symbols to the formulre of molecules ; but this 

 was not without warrant. In the form in which I have enunciated the atomic 

 theory it relates to the chemical interaction of substances, whether compound or 

 simple, and the equality of the quantities concerned is the equality of molecules, 

 since these are the quantities of substances entering into or coming out from 

 sin o-le chemical interactions. Were it nor, therefore, for fear of confounding it 

 with the mechanical theory of that name, the atomic theory should be called 

 the molecular theory of chemistry. It might, indeed, have happened to be 

 so called by its author, for Dalton has told us that he had in mind both atom 

 and molecule as names for his chemically ultimate particles, and chose the 

 former because it carried with it the notion of indivisibility. He extended also, 

 as we do, the use of the term ' atom ' to chemically compound substances, since 

 their combining quantities are chemically indivisible. 



