7- Acidify another portion strongly with acetic acid and 

 add a few drops of potassium ferrocyanide. A white precipi- 

 tate is obtained. Peptones do not give this reaction. (Al- 

 bumin is also precipitated by lead acetate, mercuric chloride ; 

 picric acid ; strong acid, e. g. , nitric ; tannin ; and strong 

 alcohol). 



8. Make some of the albumin .solution strongly acid with 

 acetic acid, add some sodium sulphate and boil. All proteids 

 except peptones are precipitated in this manner. The filtrate, 

 after boiling, can be used for other tests as the acid and sul- 

 phate do not decompose the solution. 



g. Indiffusibility of Albumin. Place some of the solution 

 in a dialyzer. The salts (cry,stalloids) diffuse readily. Test 

 for chlorides by adding a Utile silver nitrate solution to a 

 portion of the diffusate. Apply to another portion of the 

 diflusate any of the preceding tests for albumin. None will 

 be found. Albumin belongs to the group of colloid bodies. 



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

 not coagulable by heat. They are diffusible through ani- 

 mal membranes. Albumoses or proteoses are substances in- 

 termediate in constitution between albumins and peptones. 



11. 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 

 alkalis ; 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. 



12. Like albumin they are precipitated by the addition of 

 tannic acid ; they are also precipitated by alcohol. 



13. Globulins. — Globulins are proteids insoluble in water, 

 but are soluble in dilute .saline solutions. They are coagu- 

 lated by heat. Among the most important are : vitellin, 

 crystallin (globulin), myosin, fibrinoplastin (paraglobulin), 

 and fibrinogen (metaglobulin). 



