you must rob it of some of its
hydrogen. Thus C_{6}H_{5} is a group that would exist only for a moment,
since it has a great appetite for H, and we may say this appetite would
go the length of at once absorbing either one atom of H (hydrogen) or of
some similar substance or group having a similar appetite. Suppose, now,
I place some benzene, C_{6}H_{6}, in a flask, and add some nitric acid,
which, as we said, is NO_{2}OH. On warming the mixture we may say a
tendency springs up in that OH of the nitric acid to effect union with
an H of the C_{6}H_{6} (benzene) to form HOH (water), when an appetite
is at once left to the remainder, C_{6}H_{5}--on the one hand, and the
NO_{2}--on the other, satisfied by immediate union of these residues to
form a substance C_{6}H_{6}NO_{2}, nitro-benzene or "essence of
mirbane," smelling like bitter almonds. This is the first step in the
formation of aniline.

I think I have told you that if we treat zinc scraps with water and
vitriol, or water with potassium, we can rob that water of its oxygen
and set free the hydrogen. It is, however, a singular fact that if we
liberate a quantity of fresh hydrogen amongst our nitrobenzene
C_{6}H_{5}NO_{2}, that hydrogen tends to combine, or evinces an
ungovernable appetite for the O_{2} of that NO_{2} group, the tendency
being again to form water H_{2}O. This, of course, leaves the residual
C_{6}H_{5}N: group with an appetite, and only the excess of hydrogen
present to satisfy it. Accordingly hydrogen is taken up, and we get
C_{6}H_{5}NH_{2} formed, which is aniline. I told you that ammonia is
NH_{3}, and now in aniline we find an ammonia derivative, one atom of
hydrogen (H) being replaced by the group C_{6}H_{5}. I will now describe
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