902 



C. With a view to atürming the significauce of this result we 

 have examined the conduct of the self same series of salts towards 

 a benzopurpurin solution 10 times more concentrated. 



However here the quantitative estimation, used till now, could 

 not be applied unmodified; the intensity of colour of the solutions 

 was far too great to determine the differences by a simple compa- 

 rison of the layers of the liquid. 



Therefore we first tried to estimate the quantity of dyestutf by 

 precipitation with potassium alum and weighing the precipitate; in 

 doing this however fluctuating figures were obtained. Also the 

 quantity of ash in those precipitates was too small to lead to an 

 effective method. 



The colorimetric method was now modified as follows: 10 ccm. 

 of the exhausted bath were diluted to J 00 ccm. and this solution 

 was compared to one containing 1 mgr. of benzopurpurin in 500 ccm. 



The concentrations found by comparison were now multiplied 

 by ten in order to learn the cone, of the dyestuff in the exhausted 

 liquid. 



First we had convinced ourselves of the fact that, on diluting the 

 solution of 10 mgi-. in 500 ccm. to the tenfold volume a liquid 

 was obtained, the intensity of which was equal to the standard 

 solution (1 mgr.— 500 ccm.), so that this method of dilution may 

 be considered allowable. Table III gives a survey of the result 

 obtained. 



The character of the dyeing-curves is equal to that of the dye- 

 bath diluted ten times; the succession of the metal salts has remained 

 entirely the same. Now too we see magnesium join the group of 

 the alcaliue earths as the least pronounced representative. Striking 

 but not strange is the relatively trifling action which it exercises, 

 viz. it diverges remarkably from the Ca < Sr < Ba and so in that 

 group it takes a somewhat isolated place. In the group of the bi- 

 valent heavy metals zinc also seems to stand somewhat apart by 

 its relatively pronounced action. 



D. With a view to the conformity between zinc and elements 

 from the 7''' and 8'^ group in their bivalent form, the conduct of 

 manganese, iron, cobalt, and nickel was examined, to which end the 

 sulphates were chosen. Here the difücidty presented itself that the 

 salts of those metals had a colour of their own, so that a correction 

 had to be applied. First it was made out that with the salt-con- 

 centrations used, so little of the salt itself was taken up by the 

 fibre, that hereby no perceivable change of colour took place ; this 



