48 THEORY OF COLLOIDAL BEHAVIOR 



curve in Fig. 4 containing 1 per cent of originally isoelectric 

 albumin chloride we get a curve whose ordinates give the number 

 of cubic centimeters of 0.1 N HC1 in actual combination with 1 gm. 

 of originally isoelectric albumin in 100 c.c. solution (middle curve 

 Fig. 5). 



Figure 6 contains the curves whose ordinates give the amount 

 of cubic centimeters of 0.1 N HC1, H 2 S0 4 , H 2 C 2 4 , and H 3 PO 4 

 in combination with 1 gm. of originally isoelectric egg albumin at 

 different pH. It appears again that the curves for HC1 and H 2 SO 4 

 practically coincide as the purely chemical theory demands, that 

 the oxalic acid curve is higher, and that the phosphoric acid 

 curve is still higher. What is of greater importance is that for 

 the same pH the ordinates of the H 3 P0 4 curve are always approxi- 

 mately three times as high as the ordinates of the curves for HC1 

 and H 2 SO 4 . 



The results in Table II show the actual numbers of cubic 

 centimeters of each of the four acids in combination with 1 gm. 

 of originally isoelectric crystalline egg albumin in 100 c.c. solution. 

 The values for HC1 and H 2 S0 4 are identical. Those for H 3 PO 4 

 are within the limits of accuracy always three times as large as 

 those for HC1. Thus at pH 4.0, 1.7 c.c. of 0.1 N HC1 or H 2 SO 4 

 are combined with 1 gm. of albumin, while 5.3 c.c. of 0.1 N H 3 PO 4 

 are in combination; at 3.4, 3.5 c.c. of 0.1 N HC1 or H 2 SC>4 and 

 10.6 c.c. of 0.1 N H 3 PO 4 . 



In the case of oxalic acid, we notice that at pH above 3.6 the 

 number of cubic centimeters of 0.1 N oxalic acid in combination 

 with 1 gm. of albumin is less than twice that of HC1 and that the 

 difference is the greater the higher the pH. At pH = 3.2 and 

 below practically twice as many cubic centimeters of oxalic acid 

 are at the same pH in combination with 1 gm. of originally 

 isoelectric albumin as are of HC1. Thus at pH 2.6, 6.7 c.c. of 0.1 

 N HC1 and 13.3 c.c. of 0.1 N oxalic acid are in combination with 

 1 gm. of albumin; at pH 3.0, 5.0 c.c. of 0.1 N HC1 and 9.5 c.c. of 

 0.1 N oxalic acid. These figures correspond to the results to be 

 expected on the basis of Hildebrand's titration experiments 

 against inorganic bases. These titration experiments then leave 

 no doubt that these acids combine with proteins in the same 

 stoichiometric way as they combine with crystalloids. That 

 these simple facts had not been discovered earlier is the con- 



