24 A MANUAL OF PHYSIOLOGY 



Fats. 



(a) Take a little lard or olive-oil, and observe that fat is soluble in 

 ether or warm alcohol, but not in water. Put a drop of the ethereal 

 solution of fat on a piece of paper, and note that it leaves a greasy 

 stain. 



(/?) Boil a little lard with potassium hydrate in a capsule. The 

 fat is broken up into glycerine and fatty acid, and the latter unites 

 with the alkali to form a soap. Add a small quantity of a 20 per 

 cent, solution of sulphuric acid, and heat. The fatty acids are set 

 free and collect on the surface. 



(y) Emulsification. Put in one watch-glass a few drops of neutral 

 (fresh) olive-oil, and in another a few drops of a rancid oil containing 

 fatty acids. Add a dilute solution (0-25 per cent.) of sodium 

 carbonate to each. An emulsion will be formed in the second 

 watch-glass, but not in the first. Examine it under the microscope, 

 and note the globules of oil of various sizes. 



Or the watch-glasses may first be filled with the sodium carbonate 

 solution, and a drop of fresh oil then placed on the surface of the 

 solution in one and of rancid oil in the other, by means of a small 

 pipette. A creamy white ring will soon spread out from the rancid 

 oil, and cov?r the sodium carbonate solution. 



