Investigations on Gelatin. Part VIII. The Osmotic Pressure of Gelatin in Solutions of Sodium Salicylate.

THE present investigation was undertaken under the direction of Professor S. B. Schryver with a view to ascertaining the osmotic pressure of gelatin. Previous workers on this problem have not obtained their gelatin absolutely free from ash. Although the view is now commonly held that a low ash has no direct influence on the osmotic pressure it was thought desirable, since gelatin of exceptional purity has recently been prepared in this department [1923] to study the osmotic pressure of this preparation. Since the osmotic pressure of gelatin is extremely low it is necessary to employ a fairly strong solution in order to obtain a pressure which can be easily and accurately measured with a very simple osmometer such as has been used in this investigation. If water be used as the solvent it is not possible to work at ordinary room temperature owing to the formation of a gel. It was therefore decided to employ as the solvent of the gelatin a solution of sodium salicylate, which, whilst having no chemical action upon the colloid, prevents gel formation. The liquefaction of gelatin by certain salts has been proved to be entirely reversible by Briggs and Hieben [1920] and the present investigator finds this to be the case with sodium salicylate. This reversibility proves that the salt in question has no chemical action upon the gelatin. The presence of this salt also serves to keep the solution sterile. A strong solution of sodium salicylate has therefore been used as the solvent of the gelatin in all the experiments herein described.