682 APPENDIX. 



The specific gravity of its vapour, as determined by Dumas, is 

 5-337. 



To obtain an idea of the number of atoms which it may con- 

 tain, let us divide the constituents per cent, by the atomic weight 

 of each constituent. 



Carbon, . 2*| = 105-25 



'/O 



Hydrogen, v - ^ = 84-24 

 Oxygen, ^ q !*? - 10-53 



Hence the ratios of the respective atoms are, 105-25, 84-24, 

 and 10-53. It will be convenient to bring these numbers to 

 lower terms. And the simplest way is to suppose the oxygen 

 only to amount to one atom. If we calculate on this supposi- 

 tion we find, that the constituents of camphor will be, 

 Carbon, .* . 9-995 atoms, or 10 atoms. 

 Hydrogen, i.ii-j 8 do. 8 do. 



Oxygen, . 1- do. 1 do. 



Let us see how far the specific gravity of the vapour of cam- 

 phor will agree with this estimate, 



10 volumes carbon weigh, 4' 16 67 

 8 volumes hydrogen, . 0*5555 

 J- volume oxygen, ... . : 0*5555 



5-2777 



It gives us 5-2777 for the specific gravity, on the supposition that 

 the 19 atoms are condensed into one volume. But, as in most 

 organic vapours, the atoms are condensed, not into one, but into 

 two volumes, it is much more probable that the constitution 

 of camphor is C 20 H 16 O. The weight of these volumes would 

 be 10-5555, which, divided by 2, would give 5*2777, differing 

 but little from 5-337, found by Dumas. 



These examples will give the reader a sufficient idea of the 

 way in which the atomic weight is deduced from the knowledge 

 of the specific gravity of the vapour of a body whose constituents 

 have been determined by analysis. This specific gravity ought 

 to amount to half the weight of the atoms of which the vapour is 

 composed. It must be acknowledged, however, that this mode 

 of coming at the atomic weight is only conjectural : for we can- 

 not assign any reason why the atoms making up the organic 

 body constitute not one volume, or three or four volumes, but 

 always two volumes. There doubtless is a reason for it, if the 



