The term Intermediate Products is applied, in the dye industry, to those substances obtained from organic products, whether aromatic or aliphatic, which are devoid of dye character. The most important raw materials are Benzene and its homologues, Naphthalene and Anthracene, and, to a lesser extent, certain aliphatic bodies such as Methyl and Ethyl alcohol, Acetic acid, and various other less important substances which are utilized chiefly for special brands of colours.

From these raw materials the intermediate products are obtained by means of certain comparatively simple chemical operations; the hydrocarbons which serve as the starting-point are obtained by the colour factories from the tar distilleries. In many cases it is found that the yields obtained can be increased almost up to the theoretical by paying scrupulous attention to all the conditions. For this reason, as was indicated in the Introduction, the recipes have been given in almost exaggerated detail, but every technical chemist will agree with me that a good recipe cannot be given too accurately, for quite slight errors may often cause very considerable variations in the final product.

It has further been found that the manufacture of the intermediate products is far more difficult than that of the finished colouring matters, and, in addition, the apparatus and machinery needed for the intermediates occupies a far greater space than that required for the actual dyes. The Anthraquinone dyes, however, form an exception to this generalization. With the exception of this last case it may be said that the ratio of the size of the installations and the number of workmen required for intermediates and dyes respectively is approximately as 3:1, or, in other words, a colour factory which has previously purchased its intermediates and now intends to make them itself must enlarge itself about fourfold.

Further, it is found that the apparatus used for the production of Intermediates is very rapidly destroyed by the chemicals used, which is hardly surprising when one considers that for the most part they have strong acids and alkalis to deal with. For these reasons, in a well-conducted factory, all the apparatus should be fully written off.

It may be pointed out at once that the arrangement of the Intermediate Products which has been selected in the first part of this book will hardly bear serious criticism from the purely scientific standpoint. I have, for instance, under the heading of Sulphona-tions included quite a number of other operations. This arbitrary choice, however, will be found to justify itself in the sequel, since it is obviously undesirable that a product such as Aminonaphthol-disulphonic-acid 1:8:3:6 (H-acid) should be dealt with under four different headings; any such attempt would obviously be contrary to the dictates both of convenience and of common sense.

For the rest, the Index will afford any further information in cases of doubt.