JOHN H. NORTHROP 



719 



TABLE I, 



Analysis of Gelatin Solutions by Different Methods. 



Solution analyzed. 



5 per cent gelatin. 



5 per cent gelatin 

 slightly hydrolyzed 

 (Just liquefied) . 



2 per cent gelatin 

 partially hydro- 

 lyzed. 



2.5 per cent gelatin 

 nearly completely 

 hydrolyzed at pH 

 14.0 containing 0.1 

 N NazCOs. 



1 per cent gelatin ti- 

 trated directly 

 with HCl or anj' 

 strong acid. 



1 per cent gelatin ti- 

 trated directly 

 with NaOH or 

 Ba(OH). 



NH2N 



per 2 cc. 

 of 



solution, 

 Van 

 Slyke 



method. 



0.94 



0.88 



1.00 

 1.05 



5.00 

 4.80 



10.0 

 10.4 



Formol titration per 

 10 cc. of solution. 



3.00 (direct ti- 

 3.05 tration.) 



2.05 (titration to 

 pH 7.0. 



2.03 first; neu- 

 tral red 

 titration.) 



2.30 

 2.25 



11.60 

 11.50 



19.5 



20.8 



Equivalent cc. of 



0.1 N NaOH 

 calculated to 1 cc. 

 1 per cent gelatin. 



Van 

 Slyke. 



0.036 

 0.038 



0.040 



0.60 

 0.57 



0.80 

 0.84 



0.120 



0.06 



Formol. 



0.060 

 0.061 



0.040 



0.041 



0.046 

 0.045 



0.58 

 0.575 



0.83 

 0.78 



Normality 1 per cent 

 gelatin. 



0.0036 (Van 

 0.0038 Slyke). 



0.0060 (Formol). 



0.012 



0.006 



The table shows that the formol titration, if the gelatin is first 

 brought to pH 7.0, gives identical figures with that of the Van Slyke 

 determination at all stages of hydrolysis. It also shows that the 

 direct titration of gelatin without any formalin gives the same value 



