18 



To the third portion add a few drops of barium chloride 

 and let stand. A white ppt. indicate sulphates. 



To the fourth add a few drops of cone. HNO, and an 

 equal volume of ammonium molybdate solution. Let stand. 

 A yellow crystalline ppt. indicates phosphates. 



14. Peptones. Peptones are proteids soluble in water, but 

 not coagulable by heat. They are the result of proteid diges- 

 tion and are diffusible through animal membranes. Albu- 

 moses or proteoses are substances intermediate in constitution 

 between albumins and peptones. 



15. Peptones differ from albumins as follows : They are 

 not coagulated by heat ; they are not precipitated by adding 

 sodium chloride ; they are not precipitated by acids or alkalies; 

 they are not precipitated by sodium sulphate ; they are not 

 precipitated by potassium ferrocyanide ; they yield a pink 

 color with Piowtrowski's test instead of a violet as given for 

 albumin. Make a solution of peptone and apply Piowtrowski's 

 test. (See plate I). 



16. Like albumin they are precipitated by the addition 

 of tannic acid ; they are also precipitated by alcohol, but it 

 must be remembered that all proteids are precipitated by alco- 

 hol, and that the absence of other proteids must be proved 

 before decidingvthat the precipitate with alcohol is peptone. 



II 



DERIVED PROTEIDS. COMPOUND PROTEIDS. 

 ALBUMINOIDS. 



17. Acid and Alkali Albumins or Albuminates are derived 

 proteids. Alkali albuminates are obtained by the action of 

 alkalies on native proteids to such an extent that nitrogen and 

 occasionally sulphur also are eliminated from the molecule. 

 The change takes place slowly at the ordinary temperature, 

 more rapidly on heating. 



Acid albuminates are obtained by digesting native pro- 

 teids with dilute acids. 



.These albuminates are insoluble in water and in neutral 

 salt solution, but easily soluble in the presence of a small 



