JACQUES LOEB 



575 



through the addition of acid by gelatin. If H3PO4 behaves towards 

 gelatin like a monobasic acid the curves for osmotic pressure for gela- 

 tin phosphate should be identical with the curves for gelatin nitrate 

 when plotted over pH as abscissae. Fig. 7 shows that this is actu- 

 ally the case. The maximum for the two curves lies between pH 

 3.3 and 3.5 and is about 300 mm. Fig. 8 shows that the osmotic 

 pressure curves for gelatin acetate and citrate are also identical and 



300 

 Z75 

 250 

 225 

 200 

 175 

 150 

 125 

 100 



75 

 . 50 



25 







pH 25 27 29 3.1 33 3.5 37 3.9 4.1 4.3 45 47 



HN03» 

 H3PO40 



Fig. 7. Showing identity of influence of HNO3 and H3PO4 upon osmotic pres- 

 sure of gelatin solution for the same pH. 



that they agree with the curves for gelatin nitrate and gelatin phos- 

 phate as well as with those for gelatin bromide (Fig. 1). 



What is true for the osmotic pressure curves is also true for the 

 curves for the other physical properties of gelatin. Thus Fig. 9 

 gives the curves for viscosity of 1 per cent solutions of gelatin bro- 

 mide, oxalate, and tartrate, showing that they are practically iden- 

 tical when plotted with pH as abscissae. Fig. 10 gives the curves 



