OPTICAL AND ELECTRICAL PROPERTIES OF COLLOIDS 81 



distinguishable by the size of their particles, by "fractional coagula- 

 tion," l i.e., by the addition of salt solutions of progressively increas- 

 ing strength. 



The influence of neutral salts exhibits regularities which are of 

 great importance in a number of biological phenomena and which we 

 shall repeatedly encounter. The salting out of hydrophile colloids, 

 gelatinization, the irritability of muscle and nerve, the permeability 

 of cell membranes (blood corpuscles, etc.), the swelling of membranes 

 and many other phenomena are thus related to a group of physico- 

 chemical properties of solutions, whose relationship is indubitable 

 even though the true basis is not clear. With H. FRETJNDLICH we 

 shall describe these effects of neutral salts as lyotropic (solution 

 changing), and we shall study them more closely. 



Most inorganic salts increase the surface tension of water and from 

 a table of W. K. RONTGEN and J. SCHNEIDER we obtain the following 

 series for the increase in the surface tension by the alkaline iodids: 



Na > K > Li > NH 4 . 



With the anion of various alkalis: 



CO 3 > SO 4 > Cl > NO 3 > I. 



Though the compressibility, the solubility and the viscosity of 

 water are changed in a similar order by neutral salts, the relation- 

 ship is much more fundamental. Neutral salts may accelerate or 

 impede catalytic effects, such as the inversion of cane sugar, the 

 saponification of esters and the changing of acetone into diacetone 

 alcohol. The action in acid solutions is usually the reverse of what 

 it is in alkaline solutions as has been shown by R. HOBER. In acid 

 media the acceleration by cations is 



Li > Na > K > Rb > Cs, 

 in alkaline media 



Cs > Rb > K > Na > Li. 



For anions in acid solutions the following order holds: 

 I > NO 3 > Br > Cl > CH 3 CO 2 > SO 4 . 



In alkaline solution the series is reversed. 



In neutral solution also the lyotropic series holds, although small 

 changes in the arrangement may exist for some of the ions. 



1 Since reversible hydrosols are considered I might describe the procedure 

 preferably as "fractional salting out." 



It is particularly interesting to know; that according to ODEN and OnoLMthe 

 particles do not coalesce but retain their identity and when they are redissolved, 

 there are as many particles in solution as before the salting out. 



