Prof. Magnus on the Origin of Tar in Olefiant Gas. 421 



Brande*, J. Davy f, and G. Bischofff of Bonn, have engaged 

 in inquiries on coal-gas, marsh-gas, and the different carburets 

 of hydrogen. 



To these have been lately added Frankland's § excellent contri- 

 butions to our knowledge of the manufacture of gas, the object 

 of which is to prove that the process of White is to be preferred, 

 which consists in driving the gases forth from the red-hot retorts 

 by the introduction of other gases produced by the action of 

 steam upon charcoal. As, however, Frankland has only occupied 

 himself with coal-gas, which is a mixture of different gases, the 

 decomposition of the pure olefiant gas was not in his case further 

 looked into. 



An investigation which specially treats of the decomposition 

 of this gas was carried on by Marchand || . He conducted olefiant 

 gas, which was obtained from the action of sulphuric acid upon 

 alcohol, through milk of lime and sulphuric acid in order to 

 purify it, afterwards over caustic potash to dry it, and through a 

 red-hot tube which was filled with copper wire. The gas which 

 issued from this tube he analysed by conducting it through a 

 red-hot tube containing oxide of copper, and determining the 

 quantity of water and of carbonic acid formed. He found that 

 at the commencement it was almost pure marsh-gas, but after 

 the tube had attained a complete white heat, the issuing gas was 

 almost pure hydrogen. All the carbon had been separated. 



The olefiant gas generated from sulphuric acid and alcohol, 

 after it has been freed as far as possible from sulphurous acid, 

 jether, and the vapours of wine-oil, possesses a peculiar odour. 

 On conducting a quantity of such gas through a red-hot glass 

 tube, I remarked that this odour had disappeared, and that the 

 gas had assumed the smell of coal-tar. This observation was 

 the origin of the following experiments. 



In a former communication on the sulphate of carbyle, I men- 

 tioned that olefiant gas might be prepared by mixing sulphuric 

 acid in a spacious glass vessel with about the sixteenth of its weight 

 of alcohol, warming the mass until it begins to colour, and then 

 pouring through a Welter's funnel, which enters through the 

 cup of the vessel, small quantities of alcohol into the latter. 

 Since then M. Mitscherlich has proposed to introduce the alcohol 

 in the state of vapour, by boiling it beforehand in a separate vessel, 

 and conducting the vapour into the sulphuric acid, which has 

 been diluted with 30 per cent, water and heated to 165° C. 



* Philosophical Transactions for 1820, p. 11. 



f Edinburgh Journal of Science, vol. iv. p. 43. 



X Jamieson's Journal, vol. xxix. p. 309, and vol. xxx. p. 127. 



§ Annalen der Chemie und Phetrmacie, vol. lxxxii. 



|| Journal fur Praktische Chemie, vol. xxvi. p. 478. 



