206 ANIMAL PROTEINS 



There are also other facts and considerations which have 

 an important bearing upon the point under discussion. It 

 is necessary ultimately to regard true solutions of electrolytes 

 and other bodies as heterogeneous, though perhaps of a 

 rather different order. From this point of view molecules 

 and ions existing in an aqueous solution will present a surface 

 and have associated zones of compression analogous with 

 those suggested for the minute particles of gelatine. 



Now recent investigations have shown that the essential 

 physical properties of water are affected by dissolved sub- 

 stances in a definite manner and to a fixed extent, and that 

 these substances exhibit a sequence in order of their effect. 

 This sequence is also exhibited in the essential properties 

 of water as solvent and as dispersion medium for colloid sols. 

 The sequence is known as the " lyotrope series." Thus the 

 numerical value of the compressibility of aqueous solutions 

 is reduced below that of water by salts which, with the same 

 kation, exhibit an effect in the following order : 



C0 3 >S0 4 >Cl>Br>N0 3 >I 



This same order is observed, in the effect on the increased 

 values for the surface tension, density and viscosity of these 

 solutions. On the other hand, the kations have a similar 

 sequence of effects, 



Mg<NH 4 <l4<K<Na<Rb<Cs 



which appears when salts of the same anion are chosen. It 

 is not surprising to find that this lyotrope series exhibit an 

 analogous influence on the chemical reactions of water, e.g. 

 the hydrolysis of esters. In the hydrolysis by acids SO 4 

 retards the action, the other anions and the kations accelerate 

 it, in the lyotrope order. In the hydrolysis by bases the 

 series is reversed. Similarly the lyotrope series exert the 

 same order of effect upon the inversion of cane sugar and 

 other reactions. 



This lyotrope influence has also been shown to exert 

 considerable effect in the behaviour of lyophile sols. With 

 the lyophobe sols the addition of foreign substances ap- 

 parently affects the disperse phase only, but with the 



