28 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



solution of ammonium sulphate. The precipitate produced consists of the 

 globulin ; the albumin remains in solution. 



(c) Completely saturate another portion with ammonium sulphate by 

 adding crystals of the salt and grinding in a mortar a precipitate is pro- 

 duced of both the globulin and albumin. Filter. The nitrate contains no 

 protein. 



(d) Repeat the last experiment (c) with a solution of commercial peptone. 

 A precipitate is produced of the proteoses it contains. Filter. The filtrate 

 contains the true peptone. This gives the biuret reaction (see above), but 

 large excess of strong potash must be added on account of the presence of 

 ammonium sulphate. Ammonium sulphaie added to saturation precipitates 

 all proteins except peptone. 



