147 



LESSON XVII 

 THE ALBUMOSES 



1. Witte's peptone contains very little true peptone, but consists chiefly 

 ■of albmnoses, which are soluble like peptone, in neutral saline solutions. 



2. Make a solution of this substance in 10-per-cent. sodium chloride 

 solution, and filter. Very little residue is left on the filter. This consists of 

 dysalbumose, an insoluble form of hetero-albumosel formed during the process 

 of preparing the substance. If hot saline solutionj is used instead of cold as 

 a solvent, this amount of insoluble residue is increased, hetero-albumose 

 being to a slight extent precipitated by heat. 



3. The solution gives the following tests : — 



(a) Biuret reaction (due both to peptone and albumoses). 



(6) A drop of nitric acid, best added by a glass rod, gives a precipitate 

 which dissolves upon heating and reappears on cooling. (This is due to the 

 albumoses present.) 



(c) It does not coagulate on heating. 



Otherwise it gives the ordinary proteid reactions. 



4. For the separation of the albumoses and peptone proceed as follows : — 



(a) Saturate the solution with ammonixun sulphate, and filter. The 

 filtrate contains the peptone and the precipitate the albumoses. The peptone 

 is not precipitated by nitric acid, nor by most of the reagents that precipitate 

 other proteids. It is precipitated completely by alcohol, tannin, and potassio- 

 mercuric iodide ; imperfectly by phospho-tungstic and phospho-molybdic acid. 



It gives the biuret reaction, but in the presence of ammonium sulphate a 

 large excess of caustic potash is necessary. 



(b) Dialyse another portion of the solution ; hetero-albrmaose is pre- 

 cipitated. 



(c) Saturate another portion of the solution with sodium chloride (or half 

 saturate with ammonium sulphate) after faintly acidulating with acetic acid. 

 Proto-albumose and hetero-albumose are precipitated. Filter. The filtrate 

 contains the deutero-albumose and peptone. 



The proto- and hetero-albumose may be redissolved by adding distilled 

 water, and may be separated from each other by dialysis (see b). 



Deutero-albumose may be separated fi:om the peptone by saturation with 

 ammonium sulphate, or by the addition of a crystal of phosphoric acid. 

 These reagents precipitate the deutero-albumose, but not the peptone. 



Deutero-albumose gives the nitric acid reaction (see 3, 6) characteristic of 

 the albumoses only in the presence of excess of salt. If the salt is renaoved 

 by dialysis, nitric acid then causes no precipitate. 



L 2 



