THE VALENCY RULE AND THE HOFMEISTER SERIES 71 



beginning of the experiment, the ordinates the osmotic pressure 

 after equilibrium was reached. The acids used were HC1, H 2 SO4, 

 oxalic acid, and H 3 PO 4 (Fig. 15). The reader notices again that 

 the osmotic pressures are a minimum at the isoelectric point, 

 that they reach a maximum at pH a little above pH 3.2, and 

 that they then drop again. 



FIG. 15. Osmotic pressure of different albumin-acid salts. The ordinates 

 indicate the osmotic pressure (in mm. of 1 per cent albumin solution); the 

 abscissae are the pH. All solutions are 1 per cent in regard to isoelectric albumin. 

 The curves for albumin chloride and albumin phosphate are identical. 



The four curves confirm the valency rule. The curves for 

 albumin chloride and albumin phosphate are practically identical, 

 that for albumin sulphate is almost but not quite half as high as 

 that of phosphate, and the curve for oxalate is at the maximum 

 a little lower than that for chloride. 



The valency rule holds also for casein-acid salts. 1 Since 

 casein oxalate and sulphate are too sparingly soluble we can only 

 compare the osmotic pressures of casein phosphate and casein 

 chloride. The curves for the osmotic pressures of these two 

 J., J, Gen. Physiol, vol. 3, p. 547, 1920-21, 



