TRANSACTIONS OF THE SECTIONS. S3 



Prior to the time of Gerhardt, the selection of molecular weights for difl'erent 

 bodies, elementary and compound, had been almost a matter of hazard. Relying 

 conjointly upon physical and chemical phenomena, he first established definite 

 principles of selection, by pointing out the considerations upon which the determina- 

 tion of atomic weights must logically depend. Kelying upon these principles, he 

 established his classification of the non-metallic elements into monhydrides, repre- 

 sented by chlorine ; dihydrides, represented by oxygen ; trihydrides, represented by 

 nitrogen, &c. ; and, relying upon the same principles, but with a greatly increased 

 knowledge of phenomena, later chemists have given to his method a development 

 and imity, more especially as regards the metallic elements, which have secured 

 for the new system the impregnable and acknowledged position which it at present 

 occupies. The comparative unauuuity which prevailed before the time of Gerhardt 

 was the unanimity of submission to authority ; but the greater unanimity which 

 now prevails is the unanimity of conviction consequent upon an intermediate 

 period of solitary insurrection, general disturbance, and ultimate triumph. 



Bearing in mind how much the origin of the new system by Gerhardt, and ita 

 completion by his colleagues and disciples, are due to a correct appreciation of the 

 harmony subsisting between chemical and physical relations, we cannot but give 

 a hearty welcome to any large exposition of mixed chemico-physical phenomena ; 

 and, whether or not we agree with all his conclusions, there can be but one opinion 

 as to the obligation chemists are under to Professor Kopp, of Giessen, for the great 

 addition he has recently made to our knowledge and means of obtaining a further 

 knowledge of what has hitherto been but a very limited subject — namely, specific 

 heat. 



The agreement of chemists as to the elemental atomic weights is tantamount to 

 an agreement among them as to the relative quantities of the ditt'erent kinds of 

 matter which shall be represented by the difterent elemental symbols ; and this 

 brings me to the subject of chemical notation. At one time many chemists, even 

 of considerable eminence, believed and taught that Gerhardt's reformation had 

 reference mainly to notation, and not to the association and interpretation of 

 phenomena, and it became rather a fashion among them to declaim against 

 the puerilities of notational questions. That the idea is of far greater import- 

 ance than the mode of expressing it, is an obvious truism; nevertheless the 

 mode of expression has an importance of its own, as facilitating the spread of the 

 idea, and more especially its development and procreation. It has been well asked, 

 in what position woidd the science of arithmetic have been but for the substitution 

 of Ai'abic for Eoman numerals, the notation in which value is expressed by the 

 change in position for that in which it is expressed mainly by the repetition of 

 a few simple signs ? It is unfortunately too true that chemical notation is at pre- 

 sent in anything but a satisfactory state. The much-used sign of addition is, I 

 conceive, about the last one would deliberately select to represent the fine idea of 

 chemical combination, which seems allied rather, I should say, to an interpene- 

 tration than to a coarse apposition of atoms. The placing of symbols in con- 

 tiguity, or simply introducing a point between them, as indicative of a sort of 

 mvdtiplication or involution of the one atom into the other, is, I think, far pre- 

 ferable ; but here, as pointed out by Su- John Herschel, we violate the ordinary 

 algebraic understanding, which assigns very different numerical values to the ex- 



Eressions XY and X-|-Y respectively. I know, indeed, that one among us has 

 een engaged for some years past in conceiving and working out a new and strictly 

 philosophical system of chemical notation by means of actual formulae, instead of 

 mere symbols ; and I am sure that I only express the general wish of the Section 

 when I ask Sir Benjamin Brodie not to postpone the publication of his views for a 

 longer time than is absolutely necessary for their suificient elaboration. In any 

 case, however, the symbolic notation at present employed, with more or less mo- 

 dification of detail, must continue to have its peculiar uses as an instrument of 

 interpretation ; and hence the importance of our endeavoming to render it more 

 precise in meaning and consistent in its application. Many of its incongruities 

 belong to the very lowest order of convention ; such, for example, as the custom of 

 distinguishing between the representation of so-called mineral and organic com- 

 pounds, one particular sequence of symbols being habitually employed in repre- 



