the method of preparation of a small quantity of aniline, in order to
illustrate what I have tried to explain in theory. Benzene from coal-tar
is warmed with nitric acid in a flask. A strong action sets in, and on
adding water, the nitrobenzene settles down as a heavy oil, and the acid
water can be decanted off. After washing by decantation with water once
or twice, and shaking with some powdered marble to neutralise excess of
acid, the nitrobenzene is brought into contact with fresh hydrogen gas
by placing amongst it, instead of zinc, some tin, and instead of
vitriol, some hydrochloric acid (spirits of salt). To show you that
aniline is formed, I will now produce a violet colour with it, which
only aniline will give. This violet colour is produced by adding a very
small quantity of the aniline, together with some bleaching powder, to a
mixture of chalk and water, the chalk being added for the purpose of
destroying acidity. This aniline, C_{6}H_{5}NH_{2}, is a base, and forms
the foundation of all the so-called basic aniline colours. If I have
made myself clear so far, I shall be contented. It only remains to be
said that for making Magenta, pure aniline will not do, what is used
being a mixture of aniline, with an aniline a step higher, prepared from
toluene. If I were to give you the formula of Magenta you would be
astonished at its complexity and size, but I think now you will see that
it is really built up of aniline derivatives. Methyl Violet is a colour
we have already referred to, and its chemical structure is still more
complex, but it also is built up of aniline materials, and so is a basic
aniline colour. Now it is possible for the colour-maker to prepare a
very fine green dye from this beautiful violet (Methyl Violet). In fact
he may convert the violet into the green colour by heating the first
under pressure with a gas called methyl chloride (CH_{3}Cl). Methyl
Violet is constructed of aniline or substituted aniline groups; the
addition of CH_{3}Cl, then, gives us the Methyl Green. But one of the
misfortunes of Methyl Green is that if the fabric dyed with it be boiled