November 12, 1920] 



SCIENCE 



455 



ratios that the salt of a protein with a strong 

 dibasic acid, as HjSO^, however, must have 

 a divalent anion, e. g., SO^. If we compare 

 the viscosity or osmotic pressure of 1 per 

 cent, solutions of originally isoelectric gelatin 

 with diflFerent acids of the same pH we find 

 that these properties are identical for all 

 gelatin salts with monovalent anion; in other 

 words, 1 per cent, solutions of gelatin 

 chloride, bromide, nitrate, tartrate, succinate, 

 citrate, or phosphate have all the same vis- 



pH 1 Z 3 4 5 6 



Pig. 2. Influence of different acids upon the 

 swelling of gelatin when plotted over pH as ab- 

 scisssB. The curves show that nitric, trichloracetic, 

 hydrochloric, phosphoric, oxalic, and citric acids 

 cause approximately the same degree of swelling, 

 while sulfuric acid causes only ahout one half the 

 amount of swelling. In the case of gelatin sulfate 

 the anion is divalent ; in the case of the other acids 

 used it is monovalent. According to the Hofmeister 

 series the curves for phosphate, oxalate and citrate 

 should coincide with that of sulfate instead of 

 coinciding with that of chloride. 



cosity, and the same osmotic pressure at the 

 same pH. The same is true for the swelling 

 (Fig. 2). If we plot the curves for these 

 three properties with pH as abscissse and the 

 values for osmotic pressure, viscosity, and 



swelling as ordinates, we get practically iden- 

 tical curves for gelatin chloride, bromide, 

 nitrate, tartrate, succinate, citrate, and phos- 

 phate. The values for swelling are a mini- 

 num at pH 4.Y (the isoelectric point of 

 gelatin) they rise rapidly with the fall of pH 

 until they reach a maximum at pH about 3.2, 

 and then they drop again. Each curve is the 

 expression of an individual experiment. The 

 maximum in the curves for gelatin chloride, 

 bromide, nitrate, tartrate, succinate, citrate 

 and phosphate is practically identical, the 

 variations between the values for these acids 

 lying within the limit of variation which we 

 may expect if we plot six different experi- 

 ments with the same acid. When, however, 

 we plot the same curves for gelatin sulfate, 

 we get curves which are considerably lower, 

 reaching a height of only one half (or a little 

 less than) those of gelatin-acid salts with 

 monovalent anions. It may be of interest to 

 compare our curves with those expected on 

 the basis of Pauli's and Hofmeister's ion 

 series. According to the latter theory the 

 curves for phosphates, oxalates, citrates, and 

 tartrates should be in the region of the SO^ 

 curve but not in the region of the CI curve. 

 Those authors who observed such differences 

 did not measure the hydrogen ion concentra- 

 tion, attributing the effects due to the differ- 

 ence in the hydrogen ion concentration of 

 their gelatin solutions erroneously to a differ- 

 ence in the anion effect. These elementary 

 errors form the basis of a munber of specula- 

 tions current in biology and pathology. 



When we compare monobasic acids of 

 different strength, e. g., acetic, mono-, di-, and 

 trichloracetic acids, we find that the weaker 

 the acid the more acid must be contained in 

 a 1 per cent, solution of originally isoelectric 

 gelatin to bring it to the same pH. If we 

 compare the effect of these four acids on the 

 osmotic presure of gelatin we find that it is 

 (within the limits of accuracy of these ex- 

 periments) identical for the same pH. The 

 curves for the influence of these four acids 

 on the osmotic pressure of gelatin solution 

 are practically identical when plotted over the 

 pH as abscissEe; and, moreover, the curves 



