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LIV. Remarks on Chemical Notation. 

 By William Odling, M.B., F.R.S. 



To the Editors of the Philosophical Magazine and Journal, 

 Gentlemen, 



IN your last Number, Mr. J. J. Waterston brings forward some 

 interesting views on chemical notation, which he considers 

 antagonistic to the notions propounded by me in a semipopular 

 lecture upon an entirely different subject, which I delivered a 

 little while back at the Royal Institution, and upon which he 

 accordingly goes out of his way to make a not very courteous 

 onslaught, affirming that chemists in general, and Mr. Graham 

 and myself in particular, are not so well acquainted as we ought 

 to be with the relations subsisting between atoms, molecules, 

 volumes, and formulas. 



Wherefore, in order to set us right, he tells us with exquisite 

 gravity what it is that the dynamical theory proclaims as a fact — 

 namely, that "all molecules, simple or compound, in the gaseous 

 state, occupy the same volume/' — intelligence scarcely less start- 

 ling than he might have imparted by saying that, according 

 to a fundamental rule in arithmetic, the sum of two and two 

 is always four. 



Again, in the first paragraph of his communication, he 

 charges me with having contended that the molecular weight of 

 water must be represented by the number 18, and "cannot be 

 9, as might be inferred from the specific gravity of the vapour, 

 &c." Now I certainly never before heard that the vapour-den- 

 sity of any given body pointed to some particular number as the 

 expression of its molecular weight, but looked upon it as merely 

 showing the comparative molecular weight of that body in rela- 

 tion to the molecular weight of some other body chosen as a 

 standard; and taking the molecular weight of hydrogen as a 

 standard, the molecular weight of water will, I conceive, be 9, 

 or 18, or 112*5, according as we take 1 (Dalton), or 2 (Laurent 

 and Gerhardt), or 12'5 (Berzelius) for the molecular weight of 

 hydrogen. My argument, by which I still abide, was simply 

 this : if the molecular weight of muriatic acid is 36*5, then the 

 molecular weight of water is 18, and not 9. 



In illustration of what I believe to be the generally received 

 opinion among modern chemists as to the correlation of volume 

 and formula — an opinion very different from that attributed to 

 them by Mr. Waterston — I have written down in column I. the 

 ordinarily recognized molecular formulae of a few well-known 

 bodies. Each of these formulae represents the same bulk of gas, 

 whether that bulk be considered as 1, 2, 3, 4, or 100 volumes. 



