176 



THEORY OF COLLOIDAL BEHAVIOR 



(c) All the curves in Figs. 

 43 and 44 rise from a minimum 

 at pH 4.7, reach a maximum 

 (which lies at pH 3.4 or 3.5 

 for the observed, and at 3.0 

 for the calculated curves), and 

 then drop again as steeply as 

 they rose on the other side. 

 Moreover, the absolute values 

 of observed and calculated 

 osmotic pressures are almost 

 equally high, a fact which will 

 be discussed more fully a little 

 further on. 



It may be added that the 

 curve for the calculated val- 

 ues of the osmotic pressure 

 of gelatin oxalate solutions 

 agrees also with the curve for 

 the observed values of the 

 osmotic pressure of solutions 

 of the same gelatin salt, 

 both being slightly lower 

 than the curves for gelatin 

 chloride. 



In comparing the observed 

 with the calculated values for 

 osmotic pressure, the reader 

 must keep in mind that the 

 differences are exaggerated on 

 account of the fact that the 

 pressures are expressed in 

 millimeters of a column of 

 water instead of mercury. 

 If we had expressed all the 

 figures in terms of pressure of 

 mercury, as is customary, the 

 agreement would have ap- 

 peared more complete. 



