894 



Some preliiiiinan' experiments showed that the quantities of salt 

 necessary for the exhaustion of the dye-bath were indeed much 

 greater than equimolecular ; thus a solution of 1 mg. of benzopurpurin 

 in 100 ccm. H,0 or of 7«8 millimol. needed 500 mgr. Na,SO^, viz. 

 nearly 40 millimol. in order to be exhausted by 1 gram of cotton- 

 wool. 



This was affirmed with a whole series of other salts; in every 

 case the quantity of salt necessary to bring about an almost entire 

 decoloration of the bath was many times greater than the quantity 

 of benzopurpurin. 



As at the same time observations were made which might throw 

 a light on the dyeing process, the investigation was continued in a 

 quantitative way with a number of metal salts. 



The preliminary experiments were executed with solutions of 

 1 milligram of pure (salt free") benzopurpurin 4B and, in relation 

 to each other, ecpiimolecular quantities of a number of salts, in 

 100 ccm. H,0. Every time 1 gram of puiified cotton-wool, which 

 had been freed from fat, was exposed in porcelain cups during 

 10 minutes to the action of these solutions at 65°. It appeared that 

 the intensity of colour of the bath, while using sulphates of sodium, 

 potassium and ammonium was almost identical, but still not 

 completely so. 



Magnesium sulphate acts distinctly more strongly, which was to be 

 expected of the bivalent kation in regard to the acid dyestuff, 

 whereas by the tiivalent aluminium the dyestuff had already been 

 precipitated in the bath, before it could reach the fibre. 



A second series gave the following result : (see table on next page). 



So there were again distinct differences among univalent and 

 among bivalent metals. 



What is especially striking, is the fact that the stionger action 

 depends upon the place of the metal in the potential series and not 

 upon the atomic weight, as sodium not only extracts more than 



