26 W. H. E M I G 



25 hours are placed in group 4. Group 5 includes extremely 

 fugitive colors. Dyes with a light fastness of 4 or 5 have little 

 value for permanent slides. 



Class I. Nitroso Colouring Matters 



5. Naphthol Green B is an acid dye, fastness to light 2; J 

 gram in 100 ml. of distilled water and 1 ml. of 1 per cent sulfuric 

 acid. In commercial dyeing the nitroso dyes are applied using an 

 iron salt in the dye bath but in staining tissues a darker green is 

 obtained by using the iron salt separately as if it were a mordant. 

 A deficiency of tinctorial properties limits the use of Naphthol 

 Green B on paraffin sections except in plant tissues consisting of 

 dense spore masses. 



Mordant the sections of an aethalium of Fuligo, a Myxomy- 

 cete, in 1 per cent ferric ammonium sulfate for 30 minutes, rinse in 

 distilled water, and stain for from one to 24 hours. On whole 

 mounts of fungous mycelia five to ten minutes is sufficient with 

 ferric alum as a mordant, 24 hours without the mordant. 



Obelia, Sertularia, Hydra, and animals of similar size are placed 

 in 1 per cent ferric alum for 30 minutes. After a rinse in dis- 

 tilled water the objects are stained dark green in ten minutes ; thick 

 specimens are easily overstained. Without the iron alum mordant 

 six to ten hours is needed. The invertebrates stained in Naphthol 

 Green B ten minutes may be counterstained, after a rinse in dis- 

 tilled water, for 15 minutes in Direct Fast Scarlet 4BS, C. I. No. 

 327. 



Class II. Nitro Colouring Matters 



7. Picric Acid, trinitrophenol, is an acid dye, light 2 to 5; ■£ 

 gram in 95 ml. of distilled water, 5 ml. of ^ per cent potassium 

 dichromate, and \ ml. of acetic acid. Although Picric Acid is the 

 oldest of the artificial dyestufTs it is rarely used commercially as a 

 dye except in small quantities in mixtures for shading. From an 

 aqueous stain animal and plant tissues are pale yellow. With the 

 aid of potassium dichromate and acetic acid the newly developed 

 pigment appears a fast yellow which, in most tissues, is too light. 



9. Martius Yellow, Aniline Yellow, Naphthylamine Yellow is 



