33 
sulphate is either used as such, for the purpose of manure, or 
it is used for the production of other forms of ammonia in the 
pure state. Of the second, tar is a substance of great theoretical 
interest and practical importance. 
The composition of gas tar has not yet been completely in- 
vestigated ; but it is certain that 80 different bodies are contained 
in it, and probable that 20 others are present in more or less 
minute quantities, Of this large number the most important 
are as follows :— 
1. Benzene (C, Hg), toluene (Cg H; [C Hg]), and xylenes 
(C, H, [C Hs] 2). 
2. Commercial phenol, carbolic (C, H; [O H]) and cresylic 
acids (Cg H, [C H3] O H). 
3. Napthalene (C,> Hs). 
4. Creosote oils. 
5. Anthracene C,, Hy ). 
These are given in the order of their boiling points, or order of 
separation by the tar distiller. 
1. Benzene is one of the most volatile of the hydrocarbons 
(liquid at ordinary temperatures) which is contained in gas tar. 
It was first discovered by the renowned Faraday ; and it is per- 
haps one of the best examples of what is known as a condensed 
hydrocarbon, being regarded as the type of this series, known as 
“aromatic compounds.” It contains a large proportion (by 
weight) of carbon to hydrogen; and being a liquid, it is con- 
sequently highly inflammable, and when supplied with air in a 
proper manner is highly luminous. It is of great commercial 
importance as the starting point of a vast number of compounds 
which act as colouring matters. By the action upon it of nitric 
acid, nitro-benzol is prepared; and from this (by reduction) the 
famous substance—aniline—is formed. Further, by acting upon 
this, a large number of highly. important dyes—popularly called 
aniline dyes—are obtained. 
2. Phenol is the scientific name for what is often termed car- 
bolic acid. The latteris almost always commercially accompanied 
by its homologue, cresylic acid—more correctly designated cresol. 
Taking these two together, we may regard them as the most 
valuable portions of the carbolic oil produced by the tar distiller. 
By acting on phenol by nitric acid, picric acid is obtained; and 
from this a number of beautiful dyes are made. Salicylic acid— 
a valuable acquisition to modern medicine—is also prepared 
from phenol. 
3. Naphthalene (C,,H;) is one of the most stable of the sub- 
stances produced by the distillation of coal. Until the last few 
years it was difficult to sell; but by treating it with nitric acid in 
the same way that benzene was developed, a number of products 
are formed which bid fair to largely influence the dye trade. 
