420 Prof. Magnus on the Origin of Tar in defiant Gas. 



every reason to expect the existence of such intermediate acids. 

 Therefore, without further reference to the othyle theory, the 

 inquiry I had in view may be thus simply stated. In pro- 

 pionic acid, 



C9h5 \c*o 3 .h 2 o, 



C 9 h 5 J 



can one atom of the sethyle radical, conformable to Williamson's 

 alcohol and aether theory, be substituted by any other alcohol 

 radical ? 



The experiments to satisfy this inquiry furnished me with 

 conclusions which I applied to the alcohol and aether theory alone. 

 These conclusions represented Professor Williamson's theory of 

 the substitution of the aether radicals as much less probable than 

 before, especially as it was unsupported by any decisive facts, 

 but by no means represented that theory as overturned. To 

 the othyle hypothesis they did not refer, except in so far as 

 the latter is dependent upon the former. Without further dis- 

 cussing the great difficulties presented by the latter, 

 I remain, Gentlemen, 



Yours faithfully, 

 Birmingham, Oct. 24, 1853. F. Wrightson. 



LXV. On the Origin of Tar in Olefiant Gas. By G. Magnus*. 



UPWARDS of sixty years have passed since gas was first 

 applied for the purposes of illumination ; but notwith- 

 standing this, the property to which its illuminating power, and 

 consequently its entire application, is due, namely, the yielding 

 up of carbon at a red heat, is not yet quite understood. 



The Dutch physicists who discovered olefiant gas, Dieman, 

 Van Troostwyk, Lawrenberg and Bondtf, alluded in their earliest 

 communication in 1795 to the separation of carbon during its 

 combustion. Since that time various investigations have been 

 published on this gas, as well as on that derived from stone-coal. 

 Besides the repetition of the Dutch experiments by Vauquelin 

 and HechtJ at the request of the Philomathic Society of Paris, 

 Berthollet§, Th. Thomson ||, Th. De Saussuref, Dr. Henry**, 



* From Poggendorff's Annalen, vol. xc.p.l. 



t Journal de Physique, vol. xlv. p. 246. 



% Annates de Chimie, vol. xxi. p. 64. 



§ Memoires de VInstitut, vol. iv. p. 269. 



|| Proceedings of the Glasgow Philosophical Society, vol. i. p. 165. 



% Annates de Chimie,\o\. Ixxviii. p. 57- 



** Philosophical Transactions for 1808, p. 232; and for 1821, p. 136. 



