110 



CHEMICAL STATICS 



when ferric hydrate and sodium oleate were employed. Nasse 

 (49), in discussing the hypothesis that the coagulation of proteins 

 is due to the withdrawal of water from the colloid, had raised the 

 objection that the ratio of the concentrations at which the mag- 

 nesium and ammonium sulphates bring about coagulation of 

 different colloids is not always exactly the same. For different 

 colloids Nasse found the ratio 



cone, of (NH 4 )2S04 just sufficient to coagulate 

 cone, of MgSO 4 just sufficient to coagulate 



possessed the following values: 



Hofmeister, however, pointed out that the absolute concen- 

 trations which are required to bring about coagulation in these 

 cases are very different, and an exact quantitative relation of 

 this kind could not be expected to hold good, since the condition 

 of the salts in solution, or, as we should now express it, their 

 relative degree of electrolytic dissociation, differs at different 

 absolute concentrations. 



Following up the idea that the coagulation of colloids by salts 

 is attributable to the possession by the salts, in the concentra- 

 tions employed, of a greater power of binding water than that 

 possessed by colloid, Hofmeister (1890-91) took up the study of 

 the swelling or absorption of water by colloids in various solutions, 

 the degree of swelling in different solutions being regarded as a 

 measure of the relative binding capacities of the colloid and of 

 the dissolved salts. He found that in solutions of sulphates, tar- 

 trates, acetates, alcohol, cane-sugar or grape-sugar gelatin-plates 

 take up less water than they do when immersed in distilled 

 water, while in solutions of potassium, sodium or ammonium 

 chlorides, sodium chlorate, sodium nitrate and sodium bromide 

 they take up more water than they do when immersed in distilled 

 water. It will be recollected that the sulphates, tartrates and 

 acetates are the most energetic coagulants of gelatin. Regarding 

 their high coagulating power as being attributable to their power 

 of abstracting water from the protein, the interpretation of these 

 results -of Hofmeister's becomes clear. 



