Viewed with curiosity from their start, the synthetic tannins needed--like many other important discoveries--an extreme emergency for the purpose of showing their value. The Great War provided the opportunity of which chemical industry was to avail itself, and to-day we do not only see synthetic tannins placed upon the market as a veritable triumph of chemical technology and a creditable triumph of manufacturing chemistry; we also see their immensely practical qualities established as a fact, and, as the author aptly remarks, no modern tanner can to-day dissociate himself from the use of synthetic tannins for the production of leather in the true sense of this word. There is no branch of leather-making where synthetic tannins cannot help and improve processes already established. The immense number of substances patented by German manufacturing chemists for the purpose of producing synthetic tanning materials is almost staggering. In view of this fact it is doubly pleasing to see that British chemists have found new ways, and are able to produce equally good and more varied synthetic tannins than has hitherto been deemed possible. The originator of these products and his acolytes must at least share the credit with those who, in spite of the limitations necessarily set by the former, have been able to find new and better ways. In his book Dr. Grasser gives a short review of the necessary forerunner of any work upon synthetic tannins: the investigations and syntheses of the natural tannins. It is certainly to be hoped that we may soon see such works as those of Fischer's and Freudenberg's, recently published, translated into English. For the guidance of the reader it may be noted that a short account of the works of these authors may be found in the _Journal of the Society of Leather Trades' Chemists_, vol. v. (May issue); in addition to this some of the matter contained in the chapter on synthesis of tanning matters appeared in the January 1921 issue of the _Journal of the American Leather Chemists' Association._ In addition to these two sections, the last part of this book deals with the practical applications of synthetic tannins, and it is hoped that the tanner will find much valuable information in these pages. The main outlines of the synthesis of tanning matters should prove of great value to the chemist engaged in this branch of chemical technology. The translator takes great pleasure in the acknowledging the valuable assistance rendered him by Mr. Robin Bruce Croad, A.R.T.C., F.I.C., and by Mr. Arthur Harvey. F. G. A. ENNA CONTENTS Introduction: Classification of Synthetic Tannins PART I SECTION I The Synthesis of Vegetable Tannins