PROPERTIES OF GELATINE AND GLUE 217 



feeble lyotrope influence, the relatively different adsorptions 

 of its ions comes to the fore. With acids and alkalies the 

 relatively large adsorption of the hydrion and hydroxylion 

 causes this to be the predominant influence, but we must 

 concede the possibility that purely lyotrope influences may 

 be at work in some cases, and especially at the greater con- 

 centrations. Indeed, it is sometimes a difficult problem to 

 decide whether an increase or decrease in swelling is due to 

 lyotrope or adsorptive influence, but, broadly speaking, we 

 can expect strong lyotrope effects at either end of the series 

 and also at large concentrations, and we can expect strong 

 adsorptive effects in dilute solutions, in the middle of the 

 lyotrope series and in the case of alkalies and acids. 



For much of the above explanation of the nature and 

 behaviour of gelatine, the author must himself take 

 responsibility, and in this section he has freely quoted from 

 his own papers upon the subject (see References). He 

 claims that his view of a gelatine gel as involving a network 

 of compressed water, liable to modification by lyotrope 

 influence upon the continuous phase and by ionic adsorptions 

 of the disperse phase, is most in harmony with the recent 

 advances in our knowledge of colloids; that much of the 

 theory is a necessary corollary of those discoveries ; and also 

 that he has found this view to be a sound guide in practice, 

 both in tanning and in gelatine manufacture. 



Many other theories have been advanced, but most are 

 generalizations over too limited a field, and from experiments 

 with only a few substances, and show little or no correlation 

 with the wider facts of colloid behaviour. That of Procter, 

 for example, discards altogether the idea of a two-phased 

 structure of the gel as an " unproved and rather gratuitous 

 assumption," dismisses surface tension considerations as 

 " more complicated and less verified," and adsorption as 

 " wholly empirical," whilst it ignores lyotrope influence and 

 the analogy with agar gels completely. Procter's theory 

 applies mainly to the swelling of gelatine by acids, which 

 swelling he considers to be due to the osmotic pressure of 

 the anion of a highly ionizable salt formed by the chemical 



