JACQUES LOEB 275 



alkali, the "osmotic pressure falls also, but in this case a complication 

 arises, since the addition of NaOH to a gelatin-acid salt causes a 

 neutralization of the acid and the gradual transformation of the 

 gelatin-acid salt into isoelectric gelatin which has a minimal osmotic 

 pressure. 



A 1 per cent solution of metal gelatinate, e.g. Na gelatinate, has 

 its maximal osmotic pressure at a pH of about 8.4. When to a 1 per 

 cent solution of metal gelatinate of this pH alkali or neutral salt is 

 added, the osmotic pressure (as well as the swelling and the viscosity) 

 is diminished. When acid is added the same phenomenon occurs 

 but for another reason since the addition of acid lowers the pH and 

 transforms gelatin salt into isoelectric gelatin. We will first discuss 

 the action of electrolytes on the osmotic pressure of metal gelatinate. 



II. Water Charged Positively. 



Doses of 1 gm. each of commercial, finely powdered gelatin are 

 rendered isoelectric, melted, and made up into 1 per cent solutions 

 of gelatin by adding enough NaOH and water to make the volume 

 100 cc. The amount of NaOH contained in 100 cc. of each solution 

 varied and it was for different solutions 0, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2. 

 6.4, 12.8, and 25.6 cc. of m/4 NaOH. Part of this NaOH combined 

 with the gelatin, forming Na gelatinate; the rest remained free. As 

 shown in a preceding paper, there exists a definite chemical equihbrium 

 between the Na gelatinate formed, the isoelectric gelatin, and the 

 hydrogen ion concentration. If the alkali of such a solution is 

 neutralized by an acid {e.g. CO2) or if it is allowed to diffuse out from 

 the solution, the equihbrium is disturbed and some of the metal 

 gelatinate will be transformed into non-ionogenic (isoelectric) gelatin. 



These gelatin solutions containing different amounts of NaOH 

 were put into collodion bags. The latter were closed with a rubber 

 stopper which was perforated by a glass tube with a bore of 2 mm. in 

 diameter which served as a manometer to measure the osmotic pressure 

 of the solutions. These bags were put into beakers containing 350 

 cc. of a solution of NaOH which in each case had the same amount 

 of NaOH in 100 cc. solution as was originally added to the gelatin 

 solution which it surrounded. Thus the 1 per cent solution of Na 



