1804.] Dr. Hofmann on Colouring Matters derived from Coal-tar, 485 



The distillate collected in the receiver consists mainly of iodide of methyl 

 mixed with some unaltered creosote, from which it is readily liberated by 

 distillation, and agitation with a solution of caustic alkali. 



The residue contained in the retort, on being mixed with water, now readily 

 dissolves, with the exception of a small quantity of a heavy brown oil which 

 contains unaltered creosote. The aqueous solution is mixed with a large 

 quantity of water and partly saturated with carbonate of barium, the clear 

 liquid filtered off and precipitated with acetate of lead, the white preci- 

 pitate well washed and decomposed with sulphuretted hydrogen. The 

 sulphide of lead having been filtered off, the aqueous solution is now 

 carefully evaporated at a low temperature, when a thick heavy liquid is 

 obtained, which in its reactions so closely resembles pyrocatechine or oxy- 

 phenic acid, that one would be inclined to consider it identical with this 

 substance if it were not for the apparent impossibility of obtaining it in a 

 crystalline form. 



I am still engaged with the determination of the composition of the latter 

 substance ; but, from its chemical nature, so far as I have made myself ac- 

 quainted with it, and from other considerations, I think it more than 

 probable that this substance bears the closest analogy to oxyphenic acid 

 (Gg Hg O^), and is in all probability its homologue. 



The described decomposition of creosote may be expressed in the follow- 

 ing wav : — 



Creosote. Iodide of 



methyl. 



According to which creosote may be considered as methylated oxytolylic 

 acid, or oxykressylic acid. 



This view gains in probability if we consider the general properties of 

 creosote, and the fact that a lower homologue of creosote, together with free 

 oxyphenic acid, exists amongst the products of distillation of wood. Hlasi- 

 wetz has moreover shown that guaiacol is identical with this lower homo- 

 logue of creosote, which it resembles in every respect. 



If the constitution of creosote (Cg H^g turns out to be as stated above, 

 guaiacol (C^ O2) may be regarded as methylated oxyphenic acid, and 

 we may therefore expect to obtain by the action of hydriodic acid upon 

 this substance, iodide of methyl and oxyphenic acid. 



I am about to carry out the latter experiment. 



V. '^Researches on the Colouring Matters derived from Coal-tar. — 

 No. IV. Phenyltolylamine.^' By A. W. Hofmann, LL.D., 

 r.R.S. Received October 19, 1864. 

 The discovery of diphenylamine among the products of decomposition 



furnished by the destructive distillation of aniline-blue (triphenylic ros- 



