202 BIO-CHEMICAL JOURNAL 



C. Albumin 0-04 7 + CaSO 4 J!L_ + NaOH JH- 



500 1000 



D. CaSO.^- + NaOH _?L 



500 1000 



+ dye + paper. 

 Adsorbed : 



C- 75% 

 D- 98% 



It is difficult to compare with these the action of the neutral albumin 

 since acid and alkali have themselves an influence. But it appears that 

 the sign of the charge on the stable colloid determines the nature of its 

 action, although the particular albumin in this experiment had also a 

 protective action in neutral reaction. I am unable to state whether it 

 was naturally electronegative or otherwise. 



Other electro-negative dyes, such asanilin-blue and nigrosin, under 

 the action of electrolytes, give similar results to congo-red. The colloidal 

 condition of the solution is, however, apparently a sine qua non. I 

 could not detect any influence of electrolytes on picric acid, although 

 it is difficult to observe a small difference, because of the compara- 

 tively feeble colouring power of this dye. I compared the depth of 

 tint of the two solutions, one with electrolyte, the other without, in 

 both of which the same amount of paper had been immersed, by 

 placing 'them in two cells of equal thickness in front of a piece of 

 plantinotype paper and exposed to light. No difference could be 

 detected in the depth of tint on development of the paper, although, 

 as is well known, this paper shows very small d ; fferences of tone. 



Scharlach R. is interesting, because it is a so-called ' indifferent ' 

 dye, that is it does not form salts. It is insoluble in water ; but as 

 Michaelis 1 points out, when an alcoholic solution is mixed with five to 

 six times its volume of water, it is not precipitated, but becomes a 

 colloidal solution. In this state it behaves towards electrolytes like a 

 negative colloid, and, in fact, in the electric field, as I find, it wanders 

 to the anode. 



Rosolic acid shows similar properties. 



I. Deutsche, Med. Wochemch., 1904, No. 42, 



