76 THEORY OF COLLOIDAL BEHAVIOR 



Similar results were obtained in the case of the osmotic pressure 

 of metal caseinates. 



All experiments agree that only the sign and the valency of 

 the ion with which a protein is in combination determine its 

 osmotic pressure while the specific nature of the ion seems to 

 have no influence. This fact is of the greatest significance since 

 it was to be expected if colloidal behavior is due to the Donnan 

 equilibrium. The writer may state that this valency rule was 

 found before he was aware of the fact that the influence of 

 electrolytes on the osmotic pressure of protein solutions could be 

 derived from the Donnan equilibrium. 



(B) SWELLING 



It is generally stated in colloidal literature that solid blocks 

 of gelatin swell more in chlorides, bromides, or nitrates than in 

 water and that they swell less in citrates, acetates, tartrates, 

 phosphates, and sulphates than in water. The author of this 

 statement is Hofmeister 1 who was a pioneer and who cannot 

 be blamed for not considering the hydrogen ion concentration 

 of his solutions about which nothing was known at the time of 

 his experiments. In Hofmeister's experiments gelatin blocks 

 were put into salt solutions of a high concentration, and the 

 differences in the effects observed in different solutions were slight. 



He even states that sugar solutions have a dehydrating effect, 

 like certain salts, and this fact alone should have warned chemists 

 that his experiments could not be used for conclusions concerning 

 the specific effects of ions on the physical properties of colloids. 

 As far as the writer knows the discrimination between "hydrat- 

 ing" and " dehydrating" ions originated from these experiments. 



It is often asserted that Hofmeister's ion series for swelling 

 have been confirmed by other authors. Thus on page 373 of 

 Zsigmondy's book " Kolloidchemie " (2nd edition), the following 

 statements are made in support of this impression. 



"Wo. Ostwald who compared the efficiency of different acids found 

 that swelling diminishes in the acids in the following order, HC1 > 

 HNOs > acetic acid > sulphuric acid > boric acid. Fischer has shown 

 that the acid and alkali swelling of gelatin as well as that of fibrin is 



1 HOFMEISTER, F., Arch. exp. Path. u. Pharm., vol. 28, p. 210, 1891. 



