55 



1.00 

 0.90 



0.8 

 0.70 

 0.60 



0.50 

 0.40 



0.30 



0.2 



0.10 



0.05 



460 



500 



550 



600 



750 



Fig. 11. Reaction bet\^'een rhodamin B (1.8 X 10"^ Af) and 2,4-dichlo- 

 rophenol (0.011 yVl) at pH 5-9 as followed in the spectroscope. Abscissa: 

 wavelength in m/^. Ordinate: extinction. The single high curve in the 

 middle is rhodamin alone. (Dichlorophenol alone has no absorbency at 

 these wavelengths.) The family of curves has been obtained by measuring 

 the absorption at a different time after mixing the two reagents. The top 

 curve on the right was taken 7 minutes after mixing. The following lower 

 ones 5, 10, 29, 59, 89, 120, 252, and 312 minutes later. The first eight 

 went through the isobestic point on the left. Only the two last curves 

 were slightly deviating from this point (not visible in the curve), indicat- 

 ing that at this point sedimentation began to influence results (but not 

 before) . 



for its completion. What may make this sluggishness interesting 

 for the biologist is the fact that thyroxine or triiodothyronine, 

 which forms a similar complex with rhodamin, showed a similar 

 sluggishness. The biological action of thyroxine is known to need 

 24-48 hours for its full development, and may reach its maximum 

 on the tenth day after ingestion. 



