JACQUES LOEB AND ROBERT F. LOEB 



201 



Precipitation experiments give no insight into the reason why 

 sulfates are superior to chlorides in salting out; and an attempt was 

 made to get an answer by experiments on the solution of gelatin. 

 Such experiments gave the result that salts increase the solubility 

 of isoelectric gelatin, and the more, the higher their concentration 

 until finally a concentration is reached where the reverse effect is 

 noticed. This reversal occurs at a comparatively low concentration 

 in the case of the sulfates, while in th,' case of salts like CaClo or 

 MgCl2 it does not seem to occur at all in the limit of the concentrations 

 tried. The experiments were carried on at a temperature of 35°C. 



Powdered gelatin of not too small a size of grain (going through 

 sieve 30 but not through sieve 60) was rendered isoelectric in the way 

 described in previous articles, and 0.8 frm. was put into 100 cc. of 

 each of a series of solutions of NaCl, CaClo, or Na2S04 varying incon- 



TABLE III. 



Minimal Molar Concentrations Required to Precipitate 0.8 Per Cent Solutions of 



Gelatift. 



centration from m/4096 to 2 m. The suspensions of the powdered 

 gelatin were frequently stirred and the time required to practically 

 completely dissolve all the grains of powdered gelatin in suspension 

 at 35°C. was measured. We consider this tune the reciprocal of the 

 solubility. The ordinates in Fig. 4 are the solution times {i.e., the 

 reciprocal of the solubility) of isoelectric gelatin, and the abscissae 

 are the molecular concentrations of the salt used. It is obvious that 

 NaCl and still more CaClo increase the solubility (or diminish the 

 solution time) of isoelectric gelatin in water, and the more, the higher 

 the concentration of the salts. There exists a striking discontinuity 

 in the XaoSOa curve. As long as the concentration of Na2S04 is 

 below m/32 it increases the solubility of gelatin, and the more so, 

 the higher the concentration. When, however,, the concentration 



