46 W. H. E M I G 



622. Mikado Yellow G, Stilbene Yellow is a direct dye, light 

 3. The stain is lighter than Sun Yellow but it is similar in other 

 respects. 



Class VIII. Pyrazolone Colouring Matters 



640. Tartrazine is an acid dye, light 4. The bright yellow dye 

 is valued for the coloring of foodstuffs, for light filters, or for 

 orthochromatic photographic plates. 



Class IX. Ketonimine Colouring Matters 



This class includes Auramine, C. I. No. 655, a basic dye that is 

 too fugitive for use on permanent slides. 



Class X. Triphenylmethane and Diphenylnaphthylmethane Col- 

 ouring Matters 



Although the first basic dyes were made from aniline, very few 

 of the coal-tar dyes originate from that source, either directly or 

 indirectly. Because the early basic dyes were fugitive there arose 

 a popular impression that all synthetic dyes were likewise deficient 

 in fastness. Many of these dyes exhibit the phenomenon of sur- 

 face color to a marked degree. Basic Fuchsine, C. I. No. 677, is 

 red when dissolved in water; the crystals have a beautiful beetle 

 green surface which is complementary in color to that of the solu- 

 tion. Because the basic stains in pure water readily undergo a 

 partial hydrolysis of the dye salt, they are dissolved in distilled 

 water with acetic acid. On exposure to sunlight, all green basic 

 dyes fade rapidly; this is attributed partly to the greater absorp- 

 tion of light rays by green pigments. 



657. Malachite Green, China Green, Diamond Green, Solid 

 Green is a basic dye, light 4; J gram in 95 ml. of distilled water, 5 

 ml. of 5 per cent ammonium alum, and \ ml. of acetic acid. Mala- 

 cite Green is frequently used on xylem and sclerenchyma where it 

 is better than Methyl Green, C. I. No. 684. For a contrast of red 

 and green, stain the sections of plant tissues first in Crocein Scar- 

 let MOO, C. I. No. 252, Biebrich Scarlet, C. I. No. 280, or Acid 

 Fuchsine, C. I. No. 692, and follow with Malachite Green for 12 

 to 15 minutes. 



