_Classification._--In classifying the different dyestuffs and colouring
matters it is, of course, necessary to consider first the properties of
those colouring matters generally, and secondly the particular reason
for making such classification. The scientific chemist, for example,
would classify them according to theoretical considerations, as members
of certain typical groups; the representative of medical science or
hygiene would naturally classify them as poisonous and non-poisonous
bodies; whilst the dyer will as naturally seek to arrange them according
to their behaviour when applied to textile fabrics. But this behaviour
on applying to textile fibres, if varied in character according to the
chemical nature of the colouring matter, as well as the chemical and
physical nature of the fabric--and it is so varied--will make such
classification, if it is to be thorough-going, not a very simple matter.
I may tell you that it is not a simple matter, and, moreover, the best
classification and arrangement is that one which depends both on the
action of the dyes on the fibres, and also on the intrinsic chemical
character of the dyestuffs themselves. Since the higher branches of
organic chemistry are involved in the consideration of the structure and
dispositions, and consequently more or less of the properties of these
dyes, you will readily comprehend that the thorough appreciation and use
of that highest and best method of classification, particularly in the
case of the coal-tar dyes, will be, more or less, a sealed book except
to the student of organic chemistry. But it may be asked, "How does that
highest and best method of classifying the dyestuffs affect the users,
the dyers, in their processes?" In reply, I would say, "I believe that
the dyer who so understands the chemical principles involved in the
processes he carries out, and in the best methods of classifying the
dyes as chemical substances, so as to be able to act independently of
the prescriptions and recipes given him by the dye manufacturers, and so