382 Mr. W. Odling on Chemical Notation. 



1 volume serait done exactement la meme que la notation par 2 

 volumes." 



At any rate, when looked upon in this manner, not as " actually 

 representing two gaseous molecules," but as corresponding each 

 to a single volume, Gerhardt's formulae given in column I. will, 

 I should think, even in Mr. Waterston's opinion, be quite in 

 accordance with the view which regards " the ultimate moving 

 part of all the primary gases as consisting of at least two chemical 

 atoms, &c," and will also fully recognize that " splitting of the 

 gaseous molecule of oxygen into two equal parts when combining 

 with hydrogen to form water " which, thanks to the chemical 

 researches of Brodie and Laurent, is now an old story*. 



The object of my lecture at the Royal Institution, which has 

 had the misfortune to fall under Mr. Waterston's censures, was 

 not to advocate a 2- volume notation as opposed to a 1 -volume 

 notation — indeed my personal preference is inclined the other 

 way — but to show on chemical grounds that the chemical mole- 

 cule of water, if I may so say, is identical with its physical mo- 

 lecule, and consequently that this molecule f contains, not, as 

 was formerly held, the same amount of hydrogen, but double the 

 amount of hydrogen contained in the molecule of muriatic acid. 

 Or, in other words, that the molecular weights of water, muriatic 

 acid, and hydrogen are to one another as 18 : 36*5 : 2, or as 



* Brodie, in publishing some further experiments on the subject, has 

 recently given the following resume of his conclusion originally announced 

 in 1850. "On these ideas, as we regard the weight of two volumes of 

 oxygen, that is to say the weight of a molecule of oxygen, O 2 , as differing 

 from the weight of two volumes, that is, the weight of a molecule of water, 

 H 2 0, in the fact that this weight contains sixteen parts of oxygen in the 

 place of two of hydrogen, so do we regard the event of the synthesis or 

 diaeresis of oxygen as differing from the event of the synthesis or diaeresis 

 of water, in the fact that in the one change the two atoms of oxygen fulfil 

 the same functions, and are respectively in the same polar conditions as the 

 two atoms of hydrogen and the one atom of oxygen in the other. This 

 theory is of a purely relative character ; it is connected with no special 

 hypothesis as to the nature of oxygen or water, but it states that, if we make 

 a certain assertion as to the molecular nature of water, we must, in con 

 sistency, make certain parallel assertions as to the molecular nature of 

 oxygen. Our molecular hypotheses may change, but this relation will still 

 remain." (Phil. Trans. 1862, p. 837.) Laurent's research had reference 

 chiefly to the dual character of the chlorine molecule, CI 2 . 



f In accordance with the views of the school of chemists to which I 

 belong, the chemical and physical molecules of all bodies should be iden 

 tical ; but, owing doubtless to defective knowledge, some exceptions must 

 for the present be admitted. Thus there is no known chemical molecule 

 of sulphur corresponding to the physical molecule of sulphur-vapour at 

 500°, which is ninety-six times as heavy as that of hydrogen ; and, on the 

 other hand, there is no known physical molecule of phosphorus- vapour 

 corresponding to the ordinary chemical molecule of phosphorus, which is 

 thirty-one times as heavy as that of hydrogen. 





