Chemistry. — ''On the influence of sojne salts on the dyeing of 

 cellulose with Benzopurpurin 4i?". Bj Prof. J. Höeseken, 

 Mis8 G. W. Tkrgau and A. C. Binnendijk. 



(Communicated in the meeting of Nov. 30, 1918). 



I. 



The object of this investigation was originally to examine whether 

 the function of the salts in dyeing cellulose with benzidin dyestuffs 

 wa8 of a catalytic or of another nature. 



I had found with v. d. Beug and Kerstjens ^) that in acetylating 

 cellulose with acetic acid anhydride, the action of H,SC)^ and iodine 

 was purely catalytic, as small quantities of these substances were 

 sufficient to induce the attack of the very complicated cellulose 

 molecule. As cellulose is entiiely insoluble in acetic acid anhydride, 

 the substances mentioned above formed the bridge on which the 

 cellulose and tlie anhydride could meet and react on each 

 other. It was not out of the question that the anorganic salts acted 

 the same part between dyestuff and fibre material as sulphuric acid 

 between anhydride and cellulose, as far as they enabled the dyestuff 

 to enter the fibre substance. 



However it was already evident from the literature on this subject 

 that one must not speak of a catalytic action, because the metal- 

 atoms of the salts added were taken up by the fibre material, in 

 quantities which are almost equivalent to the dyestuff (as a bisul- 

 phonic acid). 



It was also known that if one wants the benzopurpurin to be 

 taken up properly by cotton wool, then there must be present in 

 the dye-bath a quantity of salt greater than an equimolecular one 

 in regard to purpurin ; this does not strike one at once because the 

 molecular weight of the purpurin is great (680) and the dyestuff' 

 solutions are frequently very diluted. In fact the phenomenon may 

 better be compared with the salting out of soaps and is considered 

 to be a shaking out by the fibre sultstauce of the dyestuff salt 

 soluble in it, of which salt the concentration in the bath is consi- 

 derably increased by the additioji of alcali-salt. 



1) Recueü 35. 320 (1916). 



58 

 Proceedings Royal Acad. Amsterdam. Vol. XXI. 



