72 GELATIN FROM CONNECTIVE TISSUE. 



wanning the fluid, reappearing as the solution cools. Sodium 

 chloride appears to assist in the precipitation if added in 

 considerable quantity (in 20 per cent solution), simply by 

 making a medium in which the precipitate is less soluble, but 

 it does not play any essential part in the reaction. Acetic 

 acid will not take the place of hydrochloric acid in this 

 reaction, neither will sodium chloride induce precipitation of 

 gelatin by mercuric chloride in the absence of acid. 



Gelatin is precipitated from aqueous solutions by saturation 

 of the fluid with ammonium sulphate, with sodium sulphate, 

 and with magnesium sulphate. 



Saturation with sodium chloride causes only a slight pre- 

 cipitate, but if acetic acid is added to the salt-saturated fluid 

 a heavy flocculent precipitate results. Hydrochloric acid will 

 take the place of acetic acid in this reaction, but the preci- 

 pitate is more soluble in excess of the acid. 



Saturation with ammonium chloride fails to produce any 

 precipitate until the fluid is acidified with acetic acid, when 

 the gelatin, in part at least, is thrown down. 



