JACQUES LOEB 261 



falls below 3.3, the swelling, osmotic pressure, and viscosity of the 

 solution diminish again upon the addition of further acid. This 

 would be explained by the ionization theory on the assumption that 

 the concentration of ionized protein in the solution reaches a maxi- 

 mum at a pH of about 3.3, and that a further increase of acid lowers 

 the concentration of ionized gelatin in the solution. The same theory 

 should also explain the fact that the curves for the physical properties 

 of gelatin salts with a bivalent ion are so much lower than the gelatin 

 salts with a monovalent ion by the assumption that the latter are 

 more highly ionized than the former. 



We can determine the concentration of ionized gelatin in solution 

 with the aid of conductivity measurements of the solution of a gelatin 

 salt, e.g. gelatin chloride, if we deduct the conductivity of the free 

 HCl in the solution from the total conductivity of the gelatin solution, 

 since our gelatin solutions contain no other electrolyte except the free 

 acid, e.g. HCl, and the gelatin salt; e.g. gelatin chloride. This is 

 proved by the fact that at the isoelectric point our gelatin solutions 

 had practically the conductivity zero (Figs. 4, 6, 8, and 9). Our 

 method of procedure was as follows: doses of 1 gm. of powdered 

 gelatin were brought to the isoelectric point and to each gram of iso- 

 electric gelatin were added different quantities of 0.1 N acid or alkali 

 and some water; the mass was melted by heating to 40° and then so 

 much H2O was added that the volume of the solution was 100 cc. 

 After that the pH of the gelatin solution and the conductivities were 

 determined. 



Fig. 4 gives the curves for such measurements in the case of gelatin 

 chloride. The abscissae are the pH, the ordinates the specific conduc- 

 tivities multiplied by 10*. The curve to the right is the total specific 

 conductivity X 10* of the gelatin chloride solution of different pH. 

 The curve to the left represents the measurements of the specific 

 conductivities X 10* of pure HCl solutions (without gelatin) for dif- 

 ferent pH. By deducting the ordinates of this latter curve from the 

 ordinates of the curve for total conductivity we get the curve in the 

 middle representing the specific conductivity X 10* of the pure gelatin 

 chloride solution. Since it had been shown before that the viscosity 

 of the solution does not influence the conductivity in this case (Hardy, 



