228 



On the Atomic Weight of Carbon. 



The discrepancies in the atomic numbers for carbon lie 

 therefore in the fourth figure, or, what is the same thing, in 

 the second decimal place. The atomic weight of carbon is 

 therefore 75*854. 



If we multiply the atomic weight of carbon as here given, 

 viz. 75-854-, by 1*1026, the specific gravity of oxygen, we ob- 

 tain as the hypothetical weight of a volume of carbon vapour 

 0-83636 ; and if to this we add 2-20520, the weight of 2 

 volumes of oxygen, and divide the sum of these by 2, we 

 obtain the number 1*521 for the specific gravity of carbonic 

 acid. 



The numbers which have been found for the specific gra- 

 vity of carbonic acid, by means of the direct weighing of the 

 gas, are — 



Sp. gr. of carb. acid. Calculated at. weight. 



By Biotand Arago 1-519 75*530 



By Berzelius and Dulong .... 1*524 76*437 



Calculated from our own analyses 1*521 75*854 



We consider it as a further proof of the correctness of the 

 atomic weight of carbon as determined by us, that our result 

 lies intermediate between those of the observations of four 

 such distinguished experimenters; and indeed all doubt must 

 be dissipated, when we reflect that with our number the differ- 

 ences observed in organic analyses are legitimately accounted 

 for*. 



* Extract of a letter from Berzelius to Professor Wohler : — 



"Aprils, 1841. 



" Baron Wrede is engaged with experiments in reference to the specific 

 gravity of gases. He has devised peculiar methods of obtaining a balloon of 

 gas in a pure state, which supersede those employed by Dulong and myself. 

 The weights of carbonic acid gas, as hitherto determined by him, nearly agree 

 with those of Dulong and myself. He has found, however, that the spe- 

 cific gravity of that gas is not the same under unequal pressures, but that 

 it diminishes with the decreased pressure until one-third of an atmosphere; 

 below this point it is constant. Its specific gravity at the ordinary pressure 



