Xanthene Dyes 203 



s25 BROM CRESOL GREEN 



pK = 4.7 



This is tetra-bromo-meta-cresol sulfonphthalein 



SO. 

 An indicator changing from yellow to blue. 



s30 CHLOR CRESOL GREEN 



pK = 4.8 

 This is tetra-chloro-meta-cresol sulfonphthalein. 



CI CI 



HO I I OH 



ci-\/\ /\/-ci 

 / c_ \ 



CHj / O CH3 



I I SO, 



An indicator changing from yellow to blue through a range only a 

 little more acid than that of methyl red. 



sS5 CHLOR PHENOL RED 



pK = 6.0 



This is di-chloro-phenol sulfonphthalein. 



HO OH 



CI C_ CI 



/ O 



I ! so. 

 \/ 



An indicator changing from yellow to red. 



