Staining Paraffin Sections 59 



in a refrigerator. Dilute the stock solution with twice its volume of 

 water for the 4-hr. schedule and with 4 parts of water for a 12-hr. 

 stain. Although the new stain will give satisfactory results, it improves 

 after 2 or 3 days. 1 he stain begins to deteriorate in a few months. 



Another type of stock solution consists of a 5 or 10% solution 

 of hematoxylin in absolute ethyl alcohol or 95% alcohol. Dilute to 

 0.5% in water as needed. 



Mordanting is sometimes necessary with the synthetic dyes des- 

 cribed in the following section. The complex problem of mordanting 

 is well summarized by Popham (1949) , and specific suggestions are 

 made throughout the present chapter. 



THE COAL-TAR DYES 



14ie coal-tar dyes comprise a large and highly diverse class of 

 synthetic dyes. Their derivation, chemical composition, and properties 

 are discussed in great detail by Conn (1936). Specify dyes that are 

 certified by the Commission on Biological Stains (Conn, 1936) . Only 

 the members of this group of stains that are in common use for 

 botanical work will be presented here. Coal-tar dyes are used in a 

 variety of solvents, and the general formulas for the most common 

 stock solutions are as follows: 



(1) 0.5 to 1% solution in water, with 5% methyl alcohol optional, as a 

 preservative. 



(2) 0.5 to 1% solution in ethyl alcohol, with alcohol concentrations of 

 50, 70, and 95% and absolute alcohol preferred by various workers. 



(3) Saturated solution in clove oil, or 



in equal volumes of clove oil and anhydrous ethyl alcohol, or 

 in methyl Cellosolve, or 



equal volumes of clo^e oil, anhydrous alcohol and methyl Cello- 

 solve. 



The following table shows the usual solvents (x) in which the 

 best known coal-tar dyes are used. 



Dye 



Acid fuchsin (acid) 



Aniline blue (acid) ( = cotton blue) 



Bismarck brown Y (basic) 



Crystal violet (basic) 



Eosin Y (acid) 



Erythrosin (acid) 



Fast green FCF (acid) 



Orange G or gold orange (acid) . . . 

 Safranin O (basic) 



Water 



X 

 X 



Alcohol, 



% 



70 

 50 

 70 



95 



95 



95 



100 



50 to 95 



Clove oil or 

 Cellosolve 



X 

 X 

 X 

 X 



