JACQUES LOEB 



36/ 



of outflow through an Ostwald viscometer is ascertained at a tem- 

 perature of 24°C. By keeping temperature and time required for 

 melting and time between completing this process and the viscosity 

 measurement constant in each case comparable results are obtained.'' 

 The time of outflow of distilled water through the viscometer was 55 

 seconds. The two curves of Fig. 1 give the values for swelling and 

 viscosity, with the logarithms of the concentration of acid used as 

 abscissae. Under each acid is found the pH for the gelatin solution 

 ascertained after the viscosity determination. 



isoelecTnc 

 poinl 



a 16 32 64 an J56 sz mn xm «m eiH law ante fssit> 

 U 1.5 1.9 M IZ 4.Z 49 54 aS 5.5 6.6 6.8 6.8 tl 6.8 



Fig. 1. Curves for viscosity and swelling of gelatin in the presence of various 

 concentrations of HBr. Abscissae, logarithms of concentration of HBr used. Un- 

 der each concentration is found the pH of the solution. Isoelectric point and 

 minimal values for curves at pH about 4.7. Both curves parallel, showing a 

 maximum at pH between 2.8 and 3.2, and a drop when pH < 2.8. 



The rest of the liquefied solution of gelatin in acid was then put 

 into bags of collodion,^ to ascertain the osmotic pressure of the gela- 

 tin solution, the pressure being expressed in mm. of height of the 

 column of 1 per cent gelatin solution in the glass tube inserted through 

 the tightly fitting rubber stopper closing the bag of collodion. The 



^ Loeb, /. Biol. Chem., 1918, xxxiv, 395. 



8 LiUie, R. S., Am. J. Physiol., 1907-08, xx, 127. Loeb, J. Biol. Chem., 1918, 

 XXXV, 497. It is hardly necessary to state that these bags are freely permeable 

 for HBr and that HBr produces no osmotic pressure when put in such bags. 

 There is a slight rise of the column of liquid in the manometer at the beginning 

 of the experiment which disappears completely in a few hours, while the rise 

 due to the gelatin, for which the membrane is impermeable, is permanent. 



