ASPECTS OF ADSORPTION PHENOMENA 201 



salt might be the actual body adsorbed by the paper. Considering the 

 great dilution of the solution, however, I do not think the latter 

 objection is very serious. 



Another property of colloids is that of being protected from 

 precipitation of electrolytes when a small amount of a stable colloid, 

 such as gelatin, is present. As pointed out by Zsigmondy, 1 the fact 

 was known to Faraday, although its meaning was, of course, not under- 

 stood at the time. The following experiment shows that gelatin also 

 protects congo-red from the action of an electrolyte : 



A. 50 c.c. H.,0 + i c.c. 0-5 % dye 



B. 50 c.c. 0-05 % gelatin + i c.c. 0-5 % dye 



C. 50 c.c. 0-038 % NaCl + 



D. 50 c.c. 0-038 % NaCl containing 0*05 % gelatin + I c.c. 0-5 % dye 



Adsorbed in three hours : 



A- 3= % C. 74 % 



B. 3i % D - 34 % 



It will be seen that Nad is practically without effect in presence of 

 gelatin. 



Egg-albumin has a similar effect, but less marked, probably on 

 account of its content in electrolytes. I did not subject it to dialysis. 

 Gelatin is stated by Victor Henri 2 to be a negative colloid ; serum- 

 albumin has recently been shown by Pauli 3 to be positive in acid 

 solution, and negative in alkaline solution. It was of interest therefore, 

 to see whether any difference in the protective action of egg-albumin 

 was to be noted in the two instances. The result showed that electro- 

 positive albumin increased the action of Caso 4 , while electro-negative 

 albumin diminished it : 



A. Albumin 0-04 % + CaSO, + H a SO 4 _5L 



1 500 1000 



B CaSO + -J , H 4 S0 4 - 



500 1000 



+ dye + paper as usual 



Adsorbed : 



A. > 80 % (partially p'li) 



B. 36% 



1. Loc. cit., p. 65, footnote. 



2. Rev. Gen. lies Sciences, 1905, p. 641. 



3. Hofmeister's Btiiragf, VII, p. 535 and p. 536. 



