802 



GELATIN AND CONDUCTIVITY 



EXPERniENTAL. 



Powdered gelatin was used in these experiments and was purified 

 at the isoelectric point according to the method described by Loeb.^ 

 The percentage of gelatin in the final solutions was determined by 

 drying samples to constant weight. The hydrogen ion concentration 

 was determined by a gas chain and the conductivity measurements 

 were made with a Kohlrausch bridge at 25°C. The physical methods 

 were standardized by simple inorganic solutions. Duplicate obser- 

 vations were made in each case. The concentrations of gelatin ranged 

 from 0.8 per cent to 6.5 per cent and the experiments were carried 

 out at three different hydrogen ion concentrations. One series of 

 observations was made at pH 5.1, near the isoelectric point of gelatin, 



TABLE I. 

 Conductivity of Pure Gelatin Solutions. 



another at ?).Z because of the relatively high ionization of gelatin at 

 that acidity, and finally one at pH 7.4, approxim.ately the reaction of 

 blood. The gelatin was brought to these hydrogen ion concentrations 

 by the addition of HCl or NaOH. 



A preliminary experiment. Table I, was carried out on pure gelatin 

 solutions varying in concentration from 0.8 per cent to 6.5 per cent 

 of gelatin. The conductivity of these solutions was determined at 

 the three different hydrogen ion concentrations mentioned above, 

 viz. 5.1, 7.4, and Z.Z. Fig. 1 shows the concentrations of gelatin as 

 the abscissae and the specific conductivities X 10""* as ordinates. 

 The curves at the three reactions are reduced to the same scale and 

 plotted at equal intervals above each other. The conductivity in- 



2 Loeb, J., J. Gen. Physiol, 1918-19, i, 341. 



