PROPERTIES OF GELATINE AND GLUE 207 



lyophile sols the effect on the continuous phase is also 

 important, and may overshadow the other. Now, in 

 gelatine and in hide gels and tanning sols we are dealing 

 with lyophile systems, and there are many points of behaviour 

 in which ly otrope influences become prominent. vSimilar effects 

 are observed upon other lyophile sols (e.g. albumin, agar-agar, 

 etc.) which differ widely in chemical nature. Thus the 

 salting out of albumin (reversible precipitation) is influenced 

 by sodium salts in lyotropic sequence as follows. The anions 

 hinder precipitation; in order of precipitating power they are : 



citrate > tartrate > SO 4 > acetate > Cl > NO 3 >C1O 3 >I>CNS 



The sulphates illustrate the kation effect, which is indepen- 

 dent and which favours precipitation : 



l4>K>Na>NH 4 >Mg 



If the experiments be carried out in faintly acid solution this 

 order of effect is exactly reversed, iodide and thiocyanate 

 having the greatest effect and citrates the least. The coagula- 

 tion temperature of albumin and the coagulation by other 

 organic substances are similarly influenced by the lyotrope 

 series. 



Lyotrope influence also exerts a powerful effect on the 

 behaviour of gelatine sols and gels. The gelation tempera- 

 ture is influenced thus : 



raised by SO 4 > citrate > tartrate > acetate 

 lowered by Cl < C1O 3 < NO 3 < Br < I 

 The kation effect (small) is Na > K > NH 4 > Mg 



Other lyotrope substances raise or lower the temperature 

 thus : 



glucose > glycerol (H 2 O) alcohol < urea 



The effect on gelation is also illustrated by the change of 

 viscosity of the sol with time. The same lyotrope order is 

 found. 



In the salting out or precipitating of gelatine with salts, 

 the order of anions is lyotrope : 



SO 4 > citrate > tartrate > acetate > Cl 



