54 W. H. E M I G 



764. Phenolphthalein is used extensively as an indicator. 



766. Fluorescein, Uranine is an acid dye, light 5 to 4. Fluo- 

 rescein does not stain plant tissues unless potassium dichromate is 

 present, whereupon, a yellow to brown is obtained which is equal to 

 Eosin in fastness. 



768. Eosin Y, 769. Methyl Eosin, 770. Ethyl Eosin, and 

 771. Eosin B are acid dyes, light 4 to 5. Few dyes are so easily 

 precipitated by acids as Eosin and Erythrosin. They are fre- 

 quently used in counterstaining bacteria, fungi, animal tissues, or 

 whole mounts. The fugitive nature of Eosin does not recommend 

 its use for permanent preparations. By adding potassium dichro- 

 mate to the stain, the fastness is improved slightly and the color is 

 changed to a darker tint. 



772. Erythrosin G, Y, and 773. Erythrosin B are acid dyes, 

 light 4 to 5 ; £ gram in 100 ml. of distilled water with or without 

 the addition of 5 ml. of \ per cent potassium dichromate. Potas- 

 sium dichromate increases the fastness and changes the color to 

 bright scarlet. Erythrosin is used as a food color. On animal tis- 

 sues Erythrosin usually blends with other dyes to yield colors of 

 little contrast. A fairly good differentiation occurs with a nuclear 

 stain in Haematoxylin followed by Erythrosin or ten minutes in 

 Erythrosin followed by Niagara Sky Blue, C. I. No. 520, for two 

 minutes. Instead of Erythrosin, try Crocein Scarlet MOO, C. I. 

 No. 252. 



Sections of plant tissues are stained one to ten hours in Ery- 

 throsin and then counterstained with Capri Blue, C. I. No. S76, 

 about five minutes, for pink and blue. This combination of stains 

 will accomplish results that are impossible with Cyanine, C. I. No. 

 806, and Magdala Red, C. I. No. 857. 



774. Phloxine B, 776. Cyanosine, 777. Rose Bengale, 778. 

 Phloxine B, 779. Rose Bengale B, and 780. Cyanosine B are 

 similar to Erythrosin in color and staining properties but they are 

 more fugitive. The addition of potassium dichromate to the stain 

 does not improve the fastness. 



781. Gallein is a mordant dye, light 1 ; J gram in 100 ml. of 

 either 1 per cent ammonium acetate or 1/10 per cent sulfuric acid. 



