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
with water, at that temperature (212 deg. F.) the colour is decomposed and
injured, for some of the methyl chloride in the compound is driven off.
In fact, by stronger heating we may drive off all the methyl chloride
and get the original Methyl Violet back again.

But we have coal-tar colours which are not basic, but rather of the
nature of acid,--a better term would be _phenolic_, or of the nature of
phenol or carbolic acid. Let us see what phenol or carbolic acid is. We
saw that water may be formulated HOH, and that benzene is C_{6}H_{6}.
Well, carbolic acid or phenol is a derivative of water, or a derivative
of benzene, just as you like, and it is formulated C_{6}H_{5}OH. You can
easily prove this by dropping carbolic acid or phenol down a red-hot
tube filled with iron-borings. The oxygen is taken up by the iron to
give oxide of iron, and benzene is obtained, thus: C_{6}H_{5}OH gives O
and C_{6}H_{6}. But there is another hydrocarbon called naphthalene,
C_{10}H_{8}, and this forms not one, but two phenols. As the name of the
hydrocarbon is naphthalene, however,