74 THEORY OF COLLOIDAL BEHAVIOR 



pressure of gelatin sulphate is in Fig. 17 also a little less than one- 

 half of the maximal osmotic pressure of gelatin chloride and the 

 maximum lies again at pH of about 3.4. The four acetic acids 

 have their maximum also at the same pH and this maximum is 

 equal to that of HC1. 1 The slight variations in the height of the 

 curves for the five monobasic acids are merely accidental and 

 probably chiefly due to slight differences in the concentration of 

 the isoelectric gelatin. In these experiments each gram of 

 powdered gelatin was brought independently to the isoelectric 

 point and in this procedure about 20 per cent of gelatin were 

 lost, but the loss varied slightly in the different experiments. 

 In the experiments represented in Fig. 14 a large quantity 

 of powdered gelatin was brought to the isoelectric point and 

 doses of 1 gm. of isoelectric gelatin were used. In this latter 

 case the quantity of originally isoelectric gelatin was always 

 the same. 



It was also found that the osmotic pressure of 0.8 per cent 

 solutions of gelatin tartrate and gelatin citrate is approxi- 

 mately the same as that of gelatin chloride of the same pH. 



The writer has also shown that the curves for the osmotic 

 pressure of 1 per cent solutions of originally isoelectric crystal- 

 line egg albumin are identical for albumin chloride, albumin 

 acetate, and albumin dichloracetate, when plotted over the pH 

 as abscissae. 1 



These experiments on gelatin and albumin leave no doubt that 

 the acetates behave like chlorides and not like the sulphates. 

 Pauli claimed that trichloracetic acid acted like sulphuric acid but 

 this is certainly not the case as far as the osmotic pressure of 

 gelatin solutions is concerned. 



The idea that the valency of the ion in combination with a 

 protein is the chief if not the only factor which influences its 

 osmotic pressure is corroborated by measurements of the osmotic 

 pressure of metal gelatinates. We had shown in Chap. IV that 

 Ca(OH) 2 and Ba(OH) 2 combine with gelatin in equivalent pro- 

 portions and that hence, the ion in combination with gelatin 

 in these cases is the bivalent cation Ca or Ba. The experiments 

 showed that Li, Na, K, and NH 4 gelatinate have about the same 

 , J., J. Gen. Physiol., vol. 3, p. 85, 1920-21. 



