Although well aware of the existence of a large literature dealing with laboratory practice, I have written this book because there does not appear to exist a suitable introduction to the fundamental operations of dye chemistry.

Ignorance of elementary facts leads in practice to waste of time, which may be redeemed in part by suitable instruction; nor should it be forgotten that many of the essential features of chemical craft may be learnt from books.

The manufacture of synthetic colours has attained to such importance that it seems desirable to familiarize the rising generation of chemical technologists with the methods of production of the more important intermediates. With this end in view, I have attempted a description of these methods in a manner which may be helpful even to those unfamiliar with technical operations.

Azo colours form the largest section of artificial dyes, and in consequence most attention has been devoted to the preparation of the necessary intermediates. As, however, many of these intermediates are also used in the synthesis of other classes of dyes, such as Indigo, Azines, Thiazines, Aniline Black, Sulphur colours, and Triphenyl-methane dyes, it may fairly be claimed that the field of synthetic colours in its essential features is covered by the present volume.

To complete the picture I have added recipes for a few dyes and included some general observations on the technique of dye manufacture. With only trifling exceptions the dyes dealt with can all be obtained from the intermediates described in the first portion, so that the student is enabled to obtain a clear view of the stages of development of a dye.

In this industry there are certain fundamental operations which are constantly repeated with slight but important modifications; for this reason I have purposely given the first few recipes in as great detail as possible, and frequent references will be made to them later.

I have also attempted to describe the processes in such a way as to give, besides the laboratory details, a clear indication of the method of carrying out the process in the works. There would be no point whatever in giving either laboratory recipes or works recipes alone, as only by an acquaintanceship with both can the budding chemist get an insight into the technical side of the dye industry, since laboratory and works must be regarded as parts of an indivisible whole.

I wish also to emphasize the fact that any process which is successful in the laboratory will also succeed on the large scale when the necessary alterations for dealing with the larger quantities involved have been made; this may, indeed, be regarded as a fundamental principle by every technical chemist.

Lastly, I would observe that the use of too little material in technical laboratory experiments leads to inaccurate results. For this reason, it is the general practice to measure the laboratory charge in gram-molecules which, multiplied by a thousand, gives at once the scale for works practice.

Too much stress cannot be laid on the fact that the material of which the apparatus is constructed plays an important part in every process; for this reason every chemist should be quite clear in his own mind as to the suitability of various materials for different chemical processes, as by this means he will be able to avoid many an unwelcome breakdown.

Objection may be taken to the fact that the patent literature of the subject has been almost entirely neglected; this, however, has been done on purpose, as the beginner is as likely as not to be confused by numerous references. Those who desire information on patents will find all they require in the excellent collections of patents compiled by Friedlaender and by Winther. In these volumes a short summary is given for each class of dyes, including references to all the important work on the subject. In my opinion, it is far better for the beginner to get a good knowledge of the few facts that he will find in any reliable text-book of organic chemistry than to attempt to become acquainted with the confusing details of innumerable patents.

The recipes given in this book must, of course, only be regarded in the light of finger-posts, and they make no claim to be the best, for many paths lead to Rome. All the examples given, however, have been actually tested by the author, and in the majority of cases they have also been put through in the works, under his supervision, so that they may be regarded as being technically satisfactory. .

H. E. F,