196 BIO-CHEMICAL JOURNAL 



the electrolytic decomposition. Colloids do behave as electrolytes, as 

 is well-known 1 , and I have made one rough determination, by 

 Whetham's boundary method, of the velocity of the coloured ion in 

 congo-red solution. At 13 the boundary, which was not very sharp, 

 moved 1 1 mm. in one hour under a potential fall of 3 volts per cm. 

 Hardy 1 finds for globulin about 7 mm. in the same time, and for 

 methylene-blue considerably more, about 40 mm. The electrical 

 conductivity of congo-red solutions is comparable with that of 

 inorganic electrolytes, a solution at 40 having a specific 



conductivity of 5600 gemmhos. I do not lay any stress on the absolute 

 value of this measurement since the preparation was not specially 

 purified, and possibly contained a small amount of inorganic salt. 



On. the whole, then, we may regard congo-red as being a 

 negatively charged colloid. As such it would be specially sensitive to 

 di- and tri-valent kations, and this is in fact the case. 



All the experiments to be described in this section, except when 

 otherwise stated, were made in the same way, viz., to 50 c.c. of the 

 solution of electrolyte 10 c.c. of dye solution and one piece 12*5 

 cm. diam. of Schleicher and Schull's extracted filter paper added. 

 After about 24 hours the amount of dye taken up by the paper was 

 estimated by taking the colorimetric value of the dye left in solution. 



It is easily seen at once that calcium salts are much more active 

 in promoting adsorption than those of the monovalent alkali metals, 

 e.g.) the amount taken up from a solution containing Caso 4 

 was 85 per cent., from a KCI 67 per cent. 



Considering this fact the effect of tap-water is not surprising, 

 since New River water contains an equivalent in c+ + ions of about 

 equal amount to the content therein of ; cso 4 . From tap-water 

 85 percent, was adsorbed in one experiment, and from distilled water 

 only 27 per cent. 3 Moreover, these facts show that in order to obtain 

 any reliable data, special care must be taken as to the purity of the 

 paper used. As an illustration, I give the following experiment : 



1. Hardy, Journal of Physiology, XXXIII, 1905, p. 292. 



2. Loc. V., p. 291 and p. 289. 



3. The absolute amounts in different experiments can only be compared by taking their ratio to the 

 amount taken up from distilled water in each case, since the temperature was not the same in all. 



