190 Dr. Thomas Thomsons Observations 



We may omit the results obtained by Cavendish and 

 Lavoisier ; because, though their experiments were made 

 with great care, their methods were not susceptible of suf- 

 ficient precision. Biot and Arago determined the specific 

 gravity of this gas, in 1807, to be 1-5196. Berzelius and 

 Dulong, in 1820, make its specific gravity 1-5245. Three 

 trials of mine, made during the summer 1820, (which 

 agreed with each other to the fourth decimal place), gave 

 the following results. 



1st Trial, . . . 1-5266 



2d Trial, . . . 1-5268 



3d Trial, . . . 1-5268 



Mean, . . • . 1-52673 



My precautions in preparing the gas were such, that I 

 have every reason to believe that it was very nearly pure. 

 Now, when charcoal is burned in oxygen gas, the bulk of 

 the gas is not altered ; it is merely converted into carbonic 

 acid. If we subtract the specific gravity of oxygen gas from 

 that of carbonic acid gas, the remainder must be the weight 

 of carbon united to a volume of oxygen gas. 



Specific gravity of carbonic acid 1-5267 

 Specific gravity of oxygen gas . 1-1111 



•4156 

 Hence, it appears that carbonic acid is a compound of 

 Oxygen . . 1-1111 or 2 

 Carbon . . 0-4156 or 0-748. 



It is evident that the atomic weight of carbon, from my 

 specific gravity of carbonic acid is -748. If we were to take 

 the specific gravity as determined by Berzelius and Dulong 

 the atomic weight of carbon would be only 0-744. The 

 reason why Berzelius makes it so high as 0-764 is, that he 

 estimates the specific gravity of oxygen gas too low. Why 

 I make the atom of carbon 0-75 instead of 0*748 will appear 

 immediately. 



3. The specific gravity of hydrogen gas was first deter- 

 mined with accuracy by me in 1820. For, when Biot and 

 Arago made their experiments in 1807, the effect of mois- 

 ture in altering the specific gravity of the very light gases 



