General Nature of Dyes 37 



In the present edition of this book the Colour Index numbers 

 (abbreviated C. I. No.) are still used, so as to avoid confusion and 

 to make the present index numbers agree with the list previously 

 published. The Schultz number of each of them is given for 

 reference purposes, however, in the lists in the appendix, pp. 252, 

 260. 



Although there has been as yet only one edition of the Colour 

 Index, a new one is now in course of preparation by the Society of 

 Dyers and Colourists in England, with the cooperation of the 

 American Association of Textile Chemists and Colorists. The 

 new edition is to be entirely different from the first, consisting of 

 more than one volume; and it will contain many more dyes than 

 ever before listed. Although work on it has been in progress for 

 some time, no probable publication date has yet been announced, 

 as the task is proving a large one. The compilers of this Index 

 are fully aware of the confusion caused by frequent changes in 

 index numbers; so it is their plan to adopt an entirely new system 

 in the second edition, with numbers so different in appearance from 

 the old ones that they cannot be confused with them. The idea is 

 to have the new numbering system one that will allow for expan- 

 sion anywhere and thus avoid the necessity of continual change 

 with each new edition. If this system works out as hoped, it is 

 possible that in the next edition of this book, the new C.I. numbers 

 can be followed. 



At the time of the fourth edition of this book, the plans for the 

 revision of the Colour Index were not known, and it was feared that 

 as soon as a second edition of that Index appeared, further refer- 

 ence to the old C. I. Numbers would be distinctly confusing. In 

 anticipation of this situation the 4th edition of the present book 

 included at the head of the description of the various dyes, a 

 series of numbers designed particularly to apply to biological 

 stains. This policy is continued in the present edition. The new 

 numbers are printed in a smaller type than the Colour Index num- 

 bers and no special significance is being given to them. It is 

 planned, however, to use them in the future under the designation 

 "Biological Stain No." only if a new edition of the Colour Index 

 makes it necessary to abandon the "C.I. Nos." at present in use 

 without furnishing more satisfactory index numbers in their place. 

 It is hoped that because of the relatively small number of dyes used 

 as biological stains and the fact that the "B.S. Nos." at present 

 selected are not entirely consecutive, there would be no need of 

 changing the significance of each number whenever a new edition 

 appears. Whether or not to use them cannot be decided until the 

 new Colour Index appears. 



DYE SOLUBILITIES 

 Textile dyes are never of a high degree of purity. Some of the 

 impurities are accidental; others are added intentionally so that 



