Mr. J. J. Waterston on Chemical Notation. 517 



must admit is as indisputable as that of the equality in the volume 

 of gaseous molecules, which Mr. Odling informs us is as clearly 

 recognized as the most simple truths of the multiplication table. 

 May we not therefore ask, Why, in the name of Cocker and com- 

 mon sense, are these numbers not given to the chemical symbolic 

 letters ? which would thus be made to express vapour-density as 

 well as molecular weight, and in compound or composite mole- 

 cules would carry the same meaning; while if bodies entered 

 into combination by fractions of molecules they would appear in 

 the formula? as such, and require no verbal discussion. 



If the specific gravity of oxygen is 16 times that of hydrogen, 

 and if the molecular weight of oxygen is 16 times that of 

 hydrogen, is not 16 associated with and 1 with H irrevo- 

 cably ? and does it not disturb this association, and therefore 

 fatally distract the attention, to give any other numerical values 

 to these symbols? I use the word fatally, because I believe that 

 serious errors as well as general confusion have arisen from this 

 apparently insignificant cause. A few of these were noticed in 

 my previous communication. It is specially when chemistry is 

 studied in its thermo-molecular relations that they assume a pro- 

 minent aspect. 



Mr. Odling states that " the object of his lecture was to show 

 on chemical grounds that the chemical molecule of water is iden- 

 tical with its physical molecule, and consequently that this mole- 

 cule contains double the amount of hydrogen contained in the 

 molecule of muriatic acid." If the lecture was delivered to 

 teach that the hydrogen of the water-molecule was double the 

 hydrogen of the muriatic acid molecule, there would have been 

 no occasion for it if the vapour- density system of chemical nota- 

 tion had been in vogue, because such facts of molecular compo- 

 sition are expressed by it so completely that any verbal addition 

 whatever becomes superfluous, e. g. water is H02 = 9, which 

 means that a gaseous molecule of water is composed of a gaseous 

 molecule of hydrogen (1), united with half a gaseous molecule 

 of oxygen (8). Muriatic acid is H* C$ = 18£, which means 

 that a gaseous molecule of muriatic acid gas is composed of 

 half a molecule of hydrogen united with half a molecule of 

 chlorine. 



The verbal explanation here appended to these formulae would 

 not of course be required if the V.D. system were fully recog- 

 nized. The difficulty of making known anything that requires 

 a little quiet application and study to master is well illustrated 

 by the formula for nitric acid given by Mr. Odling as expressed 

 on the V.D. system (Phil. Mag. p. 381), H^N^ H . Now dry 

 nitric acid is N0 2 * = 54 ; which means that a molecule of its 



