896 



preceding paragraph the investigation was extended and at the same 

 time the estimation with the naked eje in the exhausted bath was 

 replaced by a quantitative determination. 



Instead of cotton-wool 1 gram skeins of cotton were used, wliich 

 weie tirst soaked in soap water and then well linsed. During 10' 

 at 65° they were brought into a bath of 1 milligram of carefully 

 pui-ified benzopurpurin 4B and different quantities of salt in 500 

 com. of distilled water. 



After dyeing the bath was quickly cooled and compared with 

 standard solutions of known concentration in a colorimeter of 

 C. H. Wolf. 



First of all we had to examine whether Behr's law was valid, 

 viz. whether a cm. of a n. normal solution had the same intensity 

 of colour as /t./i. cm. of a Vp ''ïiormal solution, which in fact was 

 the case. 



It was necessary to use distilled water for the dilutions; water 

 for drinking gave another shade to the field by which the sensiti 

 veness was impaired. 



For benzopurpurin and with solutions of, at the utmost, 1 milli- 

 gram in 100 ccm., the sensiiiveness of the method could be increased 

 after some practice to 0.1 cm., at a thickness of the layer of 10 

 to 15 cm. viz. to less than one percent. 



After this we had to examine the relation between the quantity 

 of dyestuff, taken up by the cotton — using a fixed quantity of 

 salt — and the concentration of the dyestuff. 



Here one would expect a relation of the nature of the absorption 

 equation. 



However the quantity of dyestuff precipitated by the fibre appeared 

 to be pretty much independent of the concentration of the dyestuff 

 in tlie bath. 



To that end respectively 1, V„ '\ and \/, mgr. of benzopurpurin 

 were dissolved in 100 ccm. H,0 containing 161,2 mgr. Na,SO, 10 aq. 

 and in this sol. each time 1 gi'. of cotton was dyed during 10' at 

 65°; after that the exhausted bath was compared with the original 

 solution (see table on next page). 



It is to be expected that the independence just referred to will 

 not hold good for higher concentrations of the dyestuff. As however 

 it was our intention only to examine the influence of the electro- 

 lytes and as this effect became more lucid in this way, we confined 

 our investigations in the beginning to concentrations of not more 

 than 1 mgr. per 100 ccm. 



Moreover with these small concentrations the colorimetric deter- 



