426 Prof. Magnus on the Origin of Tar in Olefiant Gas, 



and I sometimes found, particularly when the more volatile por- 

 tion had disappeared, small white crystals within the tar which 

 were manifestly nothing else than naphthaline. We can there- 

 fore regard tar as a mixture of several hydrocarbons which are 

 isomeric with naphthaline, or as a solution of naphthaline in 

 such isomeric compounds. 



If we assume that olefiant gas is resolved only into naph- 

 thaline and marsh-gas, then eight volumes of olefiant gas are 

 necessary to form six volumes of marsh-gas and one equivalent 

 of naphthaline. 



1 Naphthaline =5C + 2H 

 6 Marsh-gas =3C + 6H. 



Hence six-eighths, or 75 per cent, of the volume of the olefiant 

 gas made use of, must remain as marsh-gas. In the experiments 

 above cited, the quantity was always something more than 75 

 per cent. But, as already remarked, the whole of the olefiant 

 gas was not decomposed ; and a portion, although a small one, 

 of the tar was also decomposed into carbon and hydrogen. 



Olefiant gas alone furnishes a tar. Marsh-gas, on the con- 

 trary, remains quite unchanged by a temperature sufficient to 

 soften the most stubborn Bohemian glass. At a white heat, 

 however, it splits into carbon and hydrogen. 



It may be concluded from this that the decomposition of the 

 olefiant gas is so effected, that at a red heat it is decomposed 

 into tar and marsh-gas ; and that both of these, the tar as well 

 as the marsh-gas, are again decomposed into carbon and hydrogen 

 at a white heat. 



Marsh-gas therefore may be regarded as a product of the 

 decomposition of olefiant gas. But olefiant gas itself is always 

 obtained by a decomposition, and is therefore to be regarded as a 

 product thereof. That this body, however, which in its chemical 

 composition and in its physical properties diverges so widely 

 from organic bodies which furnish tar, should produce the same 

 substance, was to me very surprising. 



It is a singular circumstance that the generation of tar in 

 olefiant gas has never before been observed ; the more so, as 

 among the numerous persons who exposed it to a high tempera- 

 ture several perceived an empyreumatic odour. The physicists of 

 Holland mention it*, and Berthollet corroborates the statement f. 

 G. Bischoff also J, on conducting the gas of a coal-mine through 

 a red-hot porcelain tube, remarked an empyreumatic odour, 

 which he states to have been similar to that of turpentine. He 



* Journal de Physique, vol. xlv. p. 261. 

 t Memoires de VInstitut, vol. iv. p. 299. 

 X Edinb. New Phil. Journ. vol. xxix. p. 326. 



