. JACQUES LOEB 385 



This value which was found invariably is therefore a constant which 

 we designate as "NaOH (isoelectric)." When we titrate 0.25 gm. of 

 gelatin previously treated with HBr but possessing a pH<4.7 more 

 than 5.5 cc. of 0.01 n NaOH are required for neutralization. We will 

 designate this value of NaOH as "(NaOH)„," where n represents the' 

 value of pH. If we designate the bromine number for the same pH 

 as "Bru" then we can show that the following equation is generally 

 true: (NaOH)n = NaOH (isoelectric) + Brn. In other words, titration 

 with NaOH of gelatin (previously treated with HBr) and being on 

 the acid side of its isoelectric point results in the neutralization of 

 the pure gelatin (NaOH isoelectric) with NaOH and besides in the 

 neutralization of the HBr in combination with the gelatin. This HBr 

 is set free as soon as through the addition of the NaOH the pH of 

 the gelatin solution becomes equal to 4.7. 



5. A comparison between the pH values and the bromine numbers 

 found shows that over 90 per cent of the bromine or HBr found was 

 in our experiments in combination with the gelatin. 



