OSMOTIC PRESSURE 171 



titration values, and this is probably the cause of a slight dis- 

 crepancy between observed and calculated osmotic pressures. 

 For the present we calculate z from equation (1). 



a is unknown, and we therefore can only calculate for the 

 present the values of 



2y + z - 2x 



If we express the theoretical osmotic pressure of a grammolecu- 

 lar solution in terms of millimeter pressure of a column of H 2 O we 

 get (with correction for a temperature of 24C.) 



22.4 X 760 X 13.6 X = 2.5 X 10 5 mm. 



In other words, a theoretical pressure of 2.5 mm. H^O cor- 

 responds to a concentration of 10~ 5 N. In the following tables 

 all concentrations are expressed in terms of 10~ 5 N and hence we 

 only need to multiply the values for 2y + z 2x given in our 

 tables by 2.5 to obtain the calculated osmotic pressure of the 

 gelatin solution in mm. H 2 O (neglecting the osmotic pressure of 

 the gelatin ions and molecules). 



Equation (1) holds in the case of solutions of all gelatin-acid 

 salts with monovalent anion; i.e., gelatin chloride, acetate, 

 phosphate, tartrate, citrate, etc. When, however, the anion of 

 a gelatin-acid salt is divalent, as in the case of gelatin sulphate, 

 the equilibrium equation becomes one of the third degree, as 

 has been stated in Chap. VIII. If x is the hydrogen ion con- 

 centration of the outside solution, the concentration of the SO 4 



ions in the outside solution becomes ~- If y is the concentration 



of the H ions of the free sulphuric acid in the inside solution, | 



is the concentration of the SO 4 ions of the free acid inside the 

 gelatin sulphate solution. In the case of gelatin chloride z repre- 

 sented the concentration of chlorine ions in combination with 



the gelatin; hence ~ will represent the concentration of 864 ions 

 in combination with the same number of gelatin ions. 



