STAINING, PRACTICAL AND THEORETICAL 



STAIN SOLUBILITIES AND MOLECULAR WEIGHTS 



Notes: 



The letters A, B and N indicate acid and basic neutral dyes. 



Many stains in aqueous solutions, particularly dilute aqueous solu- 

 tions, are attacked and decomposed by airborne micro-organisms when 

 kept in stock for any length of time, e.g. eosin, aniline blue. In such 

 cases it is best to add a small crystal of thymol or a few drops of chloro- 

 form as preservative. In the case of alcoholic solutions such precautions 

 are unnecessary, since the alcohol itself acts as a preservative. 



Solutions of auramine decompose when heated above 35-40° C. 

 Aqueous solutions of eosin should be prepared by using water of a 

 slightly alkaline reaction as traces of acid cause precipitation of the acid 

 radical of the dye and consequent loss of staining affinity and colour. 

 Water buffered pH 7-2-8-0 gives good results with eosin. Alkaline 

 solutions of methylene blue decompose when heated above 60-65° ^' 



Note: 



The structural formulae, solubilities, and molecular weights of other 

 dyes will be found on pages 36-76 of this book. More complete 

 information on these and many other dyes is given in Encyclopaedia 

 of Microscopic Stains (E. Gurr, i960). 



570 



