54 THE PROTEINS. [CH. II. 



cipitate, that disappears on warming and reappears on 

 cooling, either with nitric acid or potassium ferrocyanide 

 and acetic acid. They also give a precipitate in the cold 

 with copper sulphate. 



They give all the ordinary protein colour reactions, 

 with the exception of Molisch's. 



The secondary albumoses have somewhat similar pro- 

 perties to those of the primary albumoses : but they are 

 not precipitated by nitric acid, ferrocyanic acid, or copper 

 sulphate. * 



They require more than half-saturation with ammo- 

 nium sulphate to precipitate them, but are completely 

 precipitated by full saturation. Thio-albumose gives all 

 the protein colour reactions and is particularly rich in 

 sulphur (hence its name). 



Synalbumose gives the protein reactions, with the 

 exception of the glyoxylic test. 



The peptones are very soluble proteins of rather a low 

 molecular weight, so that they slowly diffuse through 

 parchment membranes. They are the only proteins not 

 precipitated by full saturation with ammonium sulphate. 

 They fail to give precipitates with Esbach's and Brucke's 

 reagents or ferrocyanic acid, but are precipitated by other 

 protein precipitants, as tannic acid, phosphotungstic acid 

 and lead acetate. 



For the following reactions make a 5 per cent, solution of " Witte's 

 peptone " in hot water, just acidify with acetic acid and filter from a small 

 amount of insoluble material (nuclein?). The solution contains all the 

 albumoses and peptones. 



50. Dilute a small amount with three or four times its bulk 

 of water, and to portions of this apply the usual colour reactions for 

 protein. They are all obtained. Note, in particular, that the biuret 

 test gives a rose colour. 



51. Boil the solution with a trace of acetic acid : it does not 

 form a coagulum. 



