1426 FOODS AND FOOD ADLTLTEEANTS. 



reaches a part of the tube where the density of the alcohol water is 

 exactly equivalent to its own. Here it remains at rest and free from 

 the action of any force save that inherent in its own molecules. 



The delicate thermometer is placed in the test tube and lowered 

 until the bulb is just above the disk. In order to secure an even tem- 

 perature in all parts of the alcohol mixture in the vicinity of the disk, 

 the thermometer is moved from time to time in a circularly pendulous 

 manner. 



The disk having been placed in position, the water in the beaker is 

 slowly heated and kept constantly stirred by means of the blowing 

 apparatus already described. 



When the temperature of the alcohol-water mixture rises to about 

 6 below the melting point, the disk of fat begins to shrivel and grad- 

 ually rolls up into an irregular mass. 



The thermometer is now lowered until the fat particle is even with 

 the center of the bulb. The bulb of the thermometer should be small, 

 so as to indicate only the temperature of the mixture near the fat. A 

 gentle rotatory movement should be given to the thermometer bulb. 

 The rise of temperature should be so regulated that the last 2 of 

 increment require about ten minutes. The mass of fat gradually 

 approaches the form of a sphere, and when it is sensibly so the read 

 ing of the thermometer is to be made. As soon as the temperature is 

 taken the test tube is removed from the bath and placed again in the 

 cooler. A second tube, containing alcohol and water, is at once placed 

 in the bath. The test tube (ice water having been used as a cooler) is 

 of low enough temperature to cool the bath sufficiently. After the 

 first determination, which should be only a trial, the temperature of 

 the bath should be so regulated as to reach a maximum of about 1.5 

 above the melting point of the fat under examination. 



The edge of the disk should not be allowed to touch the sides of the 

 tube. This accident rarely happens, but in case it should take place 

 and the disk adhere to the sides of the tube, a new trial should be made. 



Triplicate determinations should be made, and the second and third 

 results should show a close agreement. 



Example Melting point of sample of butter: Degrees. 



First trial 33. 15 



Second trial 33.05 



Third trial 33.00 



DETERMINATION OF MELTING POINT OF FATTY ACIDS. a 



Draw up the melted fatty acid into a very thin-walled capillary tube 

 1 or 2 inches long, according to the length of bulb of the thermometer 

 used. Seal one end of the tube and allow the fatty acid to cool on ice 



a U. S. Dept. Agr., Div. of Chem. Bui. 13, pt. 4, p. 448; Benedikt and Lewkowitsch, 

 Oils, Fats, and Waxes, p. 97; Wiley, Prin. and Prac. Agr. Anal., vol. 3, p. 321. 



