518 Mr. J. J. Waterston on Chemical Notation. 



vapour is composed of a molecule of nitrogen gas united with 2| 



molecules of oxygen gas ; the monohydrate by HO* . NO 2 * = 63 



if the water-molecule continues united with the acid molecule 



HO* . NO 2 * 

 when in the vapour form, or — ^ = 31^ if they separate; 



the quadrihydrate by ^ = 20*4 if they separate, and 



so on. 



The method of determining these formulae methodically by 

 simple equation in the most involved cases is given in the pre- 

 vious communication. We ought to be able to read the name 

 of a compound in its V.D. formula; and reversely we may cor- 

 rect the name by means of the same when it has been impro- 

 perly bestowed. 



But without the V.D. system, the ratio of hydrogen in the 

 water- and muriatic acid molecules might be easily proved as 

 follows : — 



In muriatic acid, one part by weight of hydrogen unites with 35*5 

 parts by weight of chlorine, and its vapour- density is 18-25 times 

 that of hydrogen. One cubic foot of muriatic acid gas contains as 

 many molecules as one cubic foot of hydrogen gas (according to 

 Mr. Odling's ridiculously clear two and two fact) ; therefore the 

 weight of each molecule of muriatic acid gas is 18*25 times that of 

 each molecule of hydrogen gas; but the proportion of the weight of 



a molecule of the acid gas that is hydrogen is only ^— part ; and 



since the molecule of the acid gas weighs 18*25 times the weight 



of the molecule of hydrogen, ■§»-? part of 18*25 is 0*5, which is 



the weight of hydrogen in a molecule of the acid gas in terms 

 of the hydrogen molecule unity. In the composition of water, 

 1 part by weight of hydrogen unites with 8 parts by weight of 

 oxygen, and the vapour-density of steam is nine times hydrogen ; 

 the weight of its molecule is nine times the hydrogen molecule, 

 and one-ninth part of the weight of the steam-molecule being 

 hydrogen, the weight of hydrogen in a steam-molecule is 1 ex- 

 pressed in terms of the hydrogen molecule unity. Thus the 

 weight of hydrogen in a molecule of muriatic acid gas is to the 

 weight of hydrogen in a molecule of water as 0*5 : 1, or as 1 : 2. 

 Q.E.D. 



Since this obvious deduction from the recognized fact of the 

 equality of gaseous molecules has escaped notice (for if it had not 

 escaped notice, how could a lecture to prove so simple a matter 

 have been thought necessary), it is not incorrect to say that the 

 arithmetical part of chemistry is not in a satisfactory condition, 



