LESSON III 



THE FATS 



LARD and olive oil are given round as examples of fats. 



1. They are insoluble in water. 



2. They dissolve readily in ether. On pouring some of the ethereal solu- 

 tion on to a piece of blotting paper, a greasy stain is left after the ether has 

 evaporated. 



3. Saponification. By boiling with potash, fat yields a solution of soap. 

 On adding some sulphuric acid to this and heating, the fatty acid collects in 

 a layer on the surface of the fluid. This experiment may conveniently be 

 performed in the following way : Melt some lard in an evaporating basin 

 and pour it into a solution of potash in alcohol ' contained in a small flask 

 and heated carefully on a water -bath nearly to boiling-point. Continue to 

 boil and saponification is soon completed. When the process is completed 

 drop some of the solution into a test-tube containing about 10 c.c. of water ; 

 the solution of soap will be clear, and no oil globules should separate out. 

 If there is any separation of oil globules continue the boiling. 



Then drop the soap solution into some 25-per-cent. sulphuric acid con- 

 tained in a small beaker and heated nearly to boiling ; the fatty acid soon 

 separates out and floats on the surface. 



4. Eeaction of Fatty Acids. (a) They produce a greasy stain on paper. 

 (&) Wash the fatty acid obtained in experiment 3 repeatedly with water, 



until the wash water is no longer acid, and divide it into two portions. 

 Dissolve one portion in ether ; this solution reacts acid to phenolphthalein ; 

 to show this, place a few drops of phenolphthalein in 5 c.c. of water contain- 

 ing a drop of 20-per-cent. potash. If this red solution is dropped into the 

 solution of fatty acid, the colour is discharged. Place the second portion of 

 fatty acid in some half- saturated solution of sodium carbonate and warm ; a 

 solution of sodium soap is obtained and carbon dioxide comes off. 



5. Separation of Neutral Fats from Fatty Acids. In most fats some 

 free fatty acid is present, They may be separated by the fact that the latter 

 only dissolves in a solution of sodium carbonate to form soap. The resulting 

 mass is shaken with water and then with ether ; the two fluids separate on 

 standing ; the ether contains the neutral fat and the water the soap. 



6. Test for Glycerin. The most important reaction for glycerin, the 

 other constituent of a fat, is the acrolein test, which is performed in the 

 following way : Place some lard in a dry test-tube, add a crystal of potassium 

 sulphate and heat. Acrolein is given off, which is recognised by its charac- 

 teristic unpleasant odour, and by the fact that it blackens a piece of filter 

 paper previously moistened with ammoniacal silver nitrate solution. 



7. Osmic Acid Test. Fat, if it contains olein or oleic acid, is blackened 

 by osmic acid. Try this with both the lard and the olive oil. 



1 30 grammes of potash are dissolved in 20 c.c. of water, and 200 c.c. of 90-per- 

 cent, alcohol added. 



