114 THE CHEMICAL COMPOSITION OF THE BODY 



FATS. 



16. Neutral Fat. a. Melting-point. Compare neutral olive oil, some 

 fresh rendered lard, and some tallow. The former is fluid at ordinary 

 room temperature. Determine the melting-points of the lard and of the 

 tallow by the method of Wiley. Fill a test-tube one-half full of water and 

 add a two-inch top layer of alcohol. Prepare a thin flake of fat and suspend 

 it in the test-tube at the dividing line of the water and alcohol. Insert the 

 bulb of a thermometer at the same level. Mount the test-tube with the 

 thermometer in a beaker on a ring stand, fill the beaker with water above the 

 level of the content of the test-tube, and gradually heat with stirring of the 

 water in the beaker. At the melting temperature the flake of fat will run 

 into a round drop. 



b. Solubility. Fat is insoluble in water, but soluble in acetone, ether, 

 chloroform, benzol, and in alcohol. 



c. Saponification. Heat some fat in an evaporating-dish, add sodium 

 hydrate, and boil. Saponification takes place. The soap is soluble in water. 

 Add 25 per cent, sulphuric acid to some of the soap, the fatty acid is liberated 

 and collects on the surface of the solution. 



17. Fatty Acids. Collect some of the fatty acids, wash to remove 

 excess of sulphuric acid, and dissolve in ether. 



a. Acid Reaction. Add an ether solution of the fatty acid to neutral 

 litmus, or to faintly alkaline phenolphthalein. The former turns red, and 

 the red of the alkaline solution of the latter is discharged. 



b. Acrolein Test. Evaporate the ether from 2 c.c. of the solution, add 

 potassium bisulphate crystals to the acid in a test-tube, and raise to a high 

 heat over a Bunsen. No acrolein is given off. Repeat on neutral fat and 

 on glycerin. Both liberate the irritating fumes of acrolein. 



18. Emulsification. a. Shake up neutral olive oil and water, no 

 emulsion is formed and the oil quickly separates. 



b. Add a couple of drops of fatty acid, a very good but temporary emul- 

 sion is now formed. 



c. Use rancid fat, a temporary emulsion is formed. 



d. Add a little soap to each of the above. A good permanent emulsion 

 is now formed, but best in c. 



19. Lipoids. a. Grind some pig's or calf's brain with ether in a 

 mortar, place in a flask with sufficient ether to make a thin suspension of 

 the material and set aside until the undissolved material has sedimented 

 completely to the bottom. Decant the clear ether and add acetone until 

 the lecithins have been precipitated. Cholesterol will crystallize from the 

 filtrate on spontaneous evaporation of the latter. Sketch the cholesterol 

 crystals. 



b. Show the presence of nitrogen in lecithin (see Exp. 2 a). 



