82 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



not precipitated with the acetic acid will be rendered insolu- 

 ble. When the solution has concentrated to about one- 

 half its original volume, this may be filtered off and the clear 

 filtrate again set evaporating until crystals begin to appear, 

 separating out of the solution (now about 20 c.c.). Keep 

 the coagulable protein precipitate. 



After allowing the solution to cool, filter off the crystals of 

 calcium phosphate and again place the filtrate over the water- 

 bath and allow it to evaporate to a thick syrup. Of what is 

 this composed? 



From the milk have now been isolated 



1. Caseinogen. 2. Fats. 3. Coagulable protein. 4. Cal- 

 cium phosphate. 5. Lactose. 



These require separate study. 



CASEINOGEN. 



This substance is a non-coagulable protein of the class of 

 phosphoproteins. It contains about 0.8% phosphorus and 

 0.7-1.2% sulphur. Caseinogen deports itself chemically 

 as a weak acid combining with bases to form soluble salts 

 or caseinogenates. The acid itself is insoluble. It exists 

 in the milk in the form of Ca-caseinogenate (apparently not 

 in a true solution, however), and when stronger acids are 

 added caseinogen is formed and falls out of solution. 



(a) Try three color-protein tests. 



(6) Test for phosphorus and sulphur by fusion. 



(c) Dissolve some in very dilute NH 4 OH and reprecipitate 

 with acetic acid. 



(d) Test for lead-blackening sulphur. 



(e) Grind up a little of the substance in a mortar with 

 CaC0 3 and water, then filter and in the filtrate test for case- 

 inogen. What chemical reaction has taken place here? 



