274 MR. JOHN LEIGH ON THE CHEMICAL CHANGES 



converted into carbonic oxide, which is evolved with the 

 gas. These are the true sources of the hydrogen and car- 

 bonic oxide in gas ; they are not necessary results of the 

 distillation, but products of the decomposition of the dis- 

 tilled matter. It has been perfectly ascertained by myself, 

 and by other chemists, that when olefiant gas is passed 

 through a nearly white hot porcelain tube, it is entirely de- 

 composed, depositing the whole of its carbon, and giving off 

 pure hydrogen gas. The late Dr. Henry subjected cannel 

 coal to distillation, beginning with a moderate heat, and 

 gradually raising it — the degree of heat is not specified, but 

 it was much inferior to that generally employed in gas 

 manufacture. 



The operation lasted 10 hours, and he examined the gas 

 at the beginning of the process, after 5 hours, and after 10 

 hours. At the beginning of the process, 100 parts of the 

 gas contained 13 of olefiant gas, 82 of light carburetted 

 hydrogen, 3 of carbonic oxide, and the rest nitrogen and 

 hydrogen. After 5 hours, 100 parts contained 7 olefiant 

 gas, 56 light carburetted hydrogen, 11 carbonic oxide, and 

 21 hydrogen. After 10 hourj, the gas contained no olefiant 

 gas, 20 light carburetted hydrogen, 10 carbonic oxide, and 

 60 hydrogen. With these analyses my own entirely accord, 

 except that, from the greater heat employed, I obtained 

 hydrogen and carbonic oxide almost from the beginning. 

 The decomposed matters occupy greater bulk than the 

 original substances from who(>e decomposition they proceed. 

 The greater the number of atoms of carbon and hydrogen 

 combined together the less space they occupy (C. 20, H. 8, 

 is a solid naphthaline); C 12, H. 6, is a liquid naphtha; C. 4, 

 H. 4, is a gas (olefiant gas). This gas, on depositing a por- 

 tion of its carbon, becoming C. 2, H. 4 (light carburetted 

 hydrogen), retained its original bulk, which latter gas is, 

 therefore, more voluminous for its composition than olefiant 

 gas. Were a gas containing 1 atom carbon and 1 atom 



