SECTION ONE 



The chromogen is responsible for colour. Associated with the 

 chromogen is an arrangement of atoms and/or groups known 

 as the chromophore. Dyes are classified into groups according to 

 their chromophores. Some of these groups are described very 

 briefly in the following pages where the structural formulae of 

 representative dyes are set out with their molecular weights and 

 solubilities in water and in absolute alcohol. Only about 80 

 examples are given here, although about 500 organic dyes are used 

 in microtechnique, as described in more detail in my earlier work 

 (Gurr, i960), to which readers are referred for further informa- 

 tion. However, the structural formulae, etc., of a number of 

 dyes, most of them new ones (e.g. trifalgic acid), and pH values, 

 given in the following pages were not available in time for in- 

 clusion in the above-mentioned work. 



For reasons stated in the book mentioned above and an earlier 

 one (Gurr, 1958a), colour index numbers were not used in either 

 of these works. Instead a system of numbering used in the 

 author's laboratories for many years was adopted. These numbers 

 will not change over the years, and the author has, therefore, 

 continued with their use in the following pages. 



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