194 



Biological Stains 



.6- 



r 



0.5- 



L. 

 460 



480 



I I I I 

 500 520 



540 



560 



Fig. 25. 

 1. PhloxineB. 



Spectral curves of three xanthene dyes: 



2. Rose Bengal. 3. Erythrosin B. 



If in the manufacture of fluorescein, dichloro or tetrachloro 

 phthalic acid is used for condensation with resorcin, a series of 

 halogenated derivatives may be obtained differing from those just 

 named by having halogen atoms in the phthalic acid residue of 

 the molecule as well as in the resorcin residue. These compounds 

 are slightly deeper in shade than the corresponding derivatives of 

 simple phthalic acid; and they are generally regarded as being of 

 more pleasing shade than the ordinary fluorescein dyes. The 

 phloxines and rose bengals are the best known of these dyes. 



