JACQUES LOEB 255 



identical (Figs. 1 and 2), proving that only the effect of the valency 

 and not that of the nature of the anion of the acid used influences the 

 swelling; since we have seen that the anion of weak dibasic or tri- 

 basic organic acids combining with the gelatin is always monovalent. 

 The curve for the swelling of gelatin sulfate, where the anion com- 

 bining with gelatin is bivalent, is only half as high as the curve for 

 the salts of gelatin with the anion of weak dibasic acids (Figs. 1 and 



^^- . . . 

 Acetic acid gives an increasing amount of swelling (Fig. 2), but it 



must be remembered that m/1 acetic acid had to be used to bring 



the pH of the gelatin to 3.0, and it is not impossible that in this case 



a secondary chemical or physical modification of the gelatin may 



complicate the conditions. 



It is of interest to compare these curves with those which should 

 be expected according to the Hofmelster series. In the latter case 

 the curves for phosphate, oxalate, citrate, tartrate, and acetate 

 should coincide with the curve for sulfate instead of coinciding with 

 the curves for CI and NO3. This difference is due to the fact 

 that the believers in the Hofmeister series did not determine the 

 pH and that they erroneously ascribed the effects due to a varia- 

 tion in the hydrogen ion concentration to a difference in the influ- 

 ence of the anion. 



The ratio between the effects of sulfuric acid on swelling and that 

 of the other acids is again not far from 1:2. If we deduct the swelling 

 of the isoelectric gelatin (of about 10 mm.) from the values of our or- 

 dinates the swelling of gelatin sulfate at pH of about Z.Z is less than 

 one-half that of the other gelatin-acid salts where the anion in com- 

 bination with gelatin is monovalent. 



When powdered isoelectric gelatin is treated with an alkali, e.g. 

 KOH, the supernatant watery solution is less acid or more alkaline 

 than the gelatin granules. The CO2 of the air lowers the pH of the 

 solutions a little but this error affects the pH of the supernatant 

 watery solution more than it does the gelatin which has a buffer action. 

 Table III, p. 252, gives the original concentration of the watery 

 solution of KOH, into 100 cc. of which 1 gm. of powdered isoelectric 

 gelatin was put (first row, Table III). After 1 hour the pH of the 

 supernatant watery solution was determined (second row, Table III) ; 



