1862.] on Mauve and Magenta, 477 



derivative, exhibits the converse deportment, resisting the action of 

 the alkali and forming a homogeneous solution with the acid. 



Each of the three coal-tar-oil-constituents which I have mentioned, 

 and of which you have characteristic specimens upon the lecture-table, 

 has received important applications in the arts and manufactures. 

 Benzol is the most convenient solvent for caoutchouc; as an agent for 

 removing oil and grease it has become an ordinary household article ; 

 phenol, when treated with nitric acid, yields us a beautiful yellow dye, 

 called by chemists carbazotic acid ; but the practical interest attached to 

 phenol you will more immediately appreciate if I tell you that this com- 

 pound presents the greatest analogy with creosote, a substance, I am 

 afraid, but too well known to most of us, — a considerable portion of 

 the creosote of commerce being in fact simply phenol ; aniline, lastly, 

 is the source of Mauve and Magenta, and must therefore claim our 

 attention more particularly this evening. 



The amount of aniline which exists in coal-tar is very limited; a 

 preparation from this source upon a sufficiently large scale could 

 never be attempted. Fortunately, chemists are in the possession of a 

 series of processes by which aniline may be produced in any quantity. 

 Benzol, the phenylated hydrogen, may readily be converted into 

 aniline, the phenylated ammonia. Let us examine this transformation 

 experimentally. 



Benzol is readily attacked by fuming nitric acid ; it dissolves in it, 

 producing a liquid of a deep-red colour. On addition of water this 

 liquid deposits a heavy yellow oil, collecting at the bottom of the 

 cylinder, perfectly different from benzol, which floats on the surface of 

 the water. The reaction will be intelligible to you, if I remind you 

 that nitric acid when referred to our types, must be viewed as a water- 

 derivative ; it is water in which, for one of the elementary hydrogen- 

 atoms, there has been substituted a compound atom, consisting of nitro- 

 gen and oxygen. 



Water. Nitric Acid. 



1—1 S 



Modern chemistry, you observe, returns to the conceptions of former 

 ages, which in the name aqua fortis appear to have anticipated in a 

 measure our present notions. 



When nitric acid acts on benzol, an interchange takes place be- 

 tween the elementary atom of the latter and the compound atom of the 

 former, nitrobenzol, the heavy yellow liquid, which we have produced, 

 and water being formed : — 



Benzol. Nitric Acid. Nitrobenzol. Water. 



(Cell,) II -f ^j^^jo = (an,)(NO.) + h}o 



