1820.] Specific Graviiij of Gases. 247 



or -125 X 36 = 4*5 = atom of chlorine. I conclude from ana- 

 logy that the atom of carbon is likewise a multiple of the atom 

 of hydrogen. Now 0-125 x 6 = 0'76. So that if 0-7.5 be the 

 weio-ht o( an atom of carbon, we see that it is just six times 

 heavier than the atom of hydrogen. 



Were we to determine the weight of an atom of carbon 

 from the specific gravity of carbonic acid gas as found in my 

 laboratory we should obtain the number 0-7481166. Now this 

 number is only ^^^th less than 0-75. I have given reasons 

 which are perfectly sufficient to satisfy every practical chemist 

 that the specific gravity of carbonic acid gas, as determined by 

 us, is rather below the truth. So that the weight of an atom of 

 carbon, as determined experimentally, cannot differ more than 

 .j.JL__th part from the theoretical number 0-75. No person the 

 least accustomed to consider the simplicity of the laws of nature 

 can, under such circumstances, entertain the least doubt that the 

 true number which represents the weiglit of an atom of carbon 

 is 0*75. The admission of it will bring carbon under the same 

 law as hydrogen, azote, and chlorine, and will introduce a sim- 

 plicity into its combinations that is truly delightful. 



I may add that Dr. WoUaston in his very useful sliding r'ale 

 has already adopted 0-75 as the weight of an atom oi carbon. 

 Dr. Prouthas done the same in his paper on the " Relation 

 between the Specific Gravities of Gaseous Bodies and the 

 Weight of their Atoms." {Aniia/s of Philosophy, vol. vi. p. 321 .) 

 Even Berzelius, who seems never to have thought oi' any rela- 

 tions subsisting between the atomic weights of different bodies, 

 but to have trusted entirely to experiment, has adopted the num- 

 ber 0-7533, w^iich does not differ so much as -j-^th pirt from 

 0-75. Indeed the number 0-75 for the weight of an atoa) cf 

 carbon has been in general use in this country for several years. 

 But if 0-75 be the weight of an atom of carbon, 0-375 must 

 represent the specific gravity of vapour of carbon, reckoning the 

 specific gravity of oxygen gas unity, or 0-41 6G, if v/e reckon 

 common air unity, as is usually done ; and tlie speciiic gravity 

 of carbonic acid gas must be just equal to that of oxygen gas 

 and of carbon added together ; that is to say, it must be 1-5277, 

 the number which I have pitched upon above. 



In giving the history of the different experiments to determine 

 the specific gravity of carbonic acid gas, I did not notice the 

 result obtained by M. T. de Saussure ; namely 1-5269. This 

 result is almost the same with ours, differing only by unity from 

 our two last trials, in the fourth decimal place. The small differ- 

 ence is in favour of M. de Saussure being on the side of accu- 

 racy. His result is nearer the truth than ours ; but the 

 difference is so small that it seemed heuxUy entitled to notice. 

 Saussure's gas must have been a mixture of 657 6 volumes of 

 carbonic acid gas and one volume of common air — a mi::ture so 



