2 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



tially of evaporated milk. The specific odor of milk becomes 

 stronger on heating. Milk which is a few days old coagulates 

 on heating. 



3. On the addition of acids, milk coagulates, the casein 

 being precipitated. 



4. When equal volumes of milk and caustic soda solution 

 are heated to boiling, the mixture becomes yellow and finally 

 brown, owing to the action of the caustic soda on the milk- 

 sugar. 



5. If we shake a few cubic centimeters of milk with one 

 and one-half to two times its volume of ether, the appearance 

 of the milk is only slightly changed, though the fat is for the 

 most part extracted. In order to show this, pour a part of 

 the ether into a watch-glass, taking care that none of the milk 

 gets into the glass. On evaporating in the air the ether 

 leaves the fat behind. If we now pour some caustic soda 

 solution down the side of the tube and mix the contents by 

 shaking gently, the milk becomes almost clear. This shows 

 that the white color of milk is due only in small part to the 

 fat which it contains; to a much greater extent it is due to 

 the swollen casein (and calcium phosphate). 



6. When some tincture of guaiacum (made by dissolving 

 some gum guaiacum in alcohol in a test-tube) is added to a 

 little milk, then some old oil of turpentine, and the mixture 

 shaken, it becomes blue. The color appears first at the sur- 

 face of contact of the milk and the oil of turpentine (Kowa- 

 lewsky). Boiled milk does not show this reaction. Milk, 

 blood or blood-pigment, and the pus-cells possess this prop- 

 erty in common. To distinguish boiled milk from unboiled, 

 the following method of Schaffer is also recommended: add 

 to 10 cc. of milk one drop of a 0.2 per cent, solution of hydro- 

 gen peroxide and two drops of a 2 per cent, solution of para- 

 phenylene diamine. Fresh milk turns blue, boiled milk does 

 not. 



