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.
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