66 THEORY OF COLLOIDAL BEHAVIOR 



ions, e.g., Cl and CH 3 COO, on the osmotic pressure or viscosity 

 of protein solutions, it is absolutely necessary to do so at the 

 same pH and the same concentration of originally isoelectric 

 protein. If this is done, it will be found that the Hofmeister 

 series have practically no real significance and that essentially 

 only the valency, not the specific nature of the ion in combination 

 with the protein, influences its physical properties. 



In the preceding chapter it was seen that at the same pH three 

 times as many cubic centimeters of 0.1 N H 3 PO4 as of HNOsare in 

 combination with 1 gm. of originally isoelectric gelatin in 100 c.c. 

 of solution. From this it follows that the anion of gelatin phos- 

 phate is the monovalent ion H2PO4 and not the trivalent anion 

 P0 4 . It follows likewise from the combining ratios discussed in 

 Chap. IV that the anion of oxalic acid in combination with 

 protein below pH = 3.0 is the monovalent anion HC2O4, while at 

 pH above 3.0 the oxalic acid dissociates to an increasing degree as 

 a dibasic acid, forming a divalent anion C2O4 with protein. The 

 same must be true, mutatis mutandis, for all weak dibasic or 

 tribasic acids, e.g., citric, tartaric, or succinic acids, namely, that 

 at pH below 4.7 they form protein salts with chiefly monovalent 

 anions. It follows also from the combining ratios, that the salt 

 of a protein with a strong dibasic acid, as H 2 SO4, must have a 

 divalent anion, e.g., SO 4 . On the basis of our valency rule, we 

 should, therefore, expect that the osmotic pressure of 1 per cent 

 solutions of originally isoelectric gelatin with different acids of 

 the same pH should be identical for all gelatin salts with monova- 

 lent anion; in other words, 1 per cent solutions of gelatin chloride, 

 bromide, nitrate, tartrate, succinate, citrate, or phosphate should 

 all have about the same osmotic pressure and the same viscosity 

 at the same pH; and the same should be true for swelling; while 

 gelatin sulphate, which has a bivalent anion, should have a much 

 lower osmotic pressure, viscosity, or swelling. We will show 

 first that this is true for the osmotic pressure of protein solutions. 



The simple method of R. S. Lillie 1 was employed for the measure- 

 ment of the osmotic pressure of gelatin solutions. Collodion 

 bags of a volume of about 50 c.c. were cast in Erlenmeyer flasks 

 assuming the shape of the latter. These were prepared in a 

 uniform way, as follows: Collodion (Merck, 275 grains of ether 



1 LILLIE, R. S., Am. J. PhysioL, vol. 20, p. 127, 1907-08. 



