204 Biological Stains 



s40 BROM PHENOL RED 



pK = 6.2 



This is di-bromo-phenol sulfonphthalein. 



HO OH 



\/\ /\/ 



Br C_ Bi 



/ O 



1 I SO. 



\/ 



An indicator changing from yellow to red through a range almost 

 identical with that of the better known brom cresol purple. It is 

 recommended in place of the latter because it is free from trouble- 

 some dichromatism. 



45 BROM CRESOL PURPLE 



pK = 6.3 



This is di-bromo-ortho-cresol sulfonphthalein: 



CH3 CH3 

 HO I I OH 



Br C_ Br 



O 



s \ 



rsoa 



A well-known indicator changing from yellow to purple. It has 

 been used by McMaster and Parsons (1938) as a vital stain. 



850 BROM THYMOL BLUE 



pK = 7.0 

 This is di-bromo-thymol sulfonphthalein: 



OH3 v^H3 CH3 CH3 



CH CH 



HO I I OH 



Br I \ / I Br 

 CHj C CH3 



/ o 



,/\ I 



I SO. 



