EDIBLE FATS AND OILS. 



133 



Press B against A and bring F bark into its original position by turning it in the 

 .,]>]> osite direction. Adjust the mirror until it gives the sharpest reading. If 

 :li- reading be not distinct after running water of a constant temperature 

 through the instrument for some time, the fat is not evenly distributed on the 

 surfaces of the prism and the process must be repeated. The instrument should 

 lx> carefully adjusted by means of the standard fluid which is supplied. As the 

 index of ivfrat-tion is greatly affected by temperature, care must be used to keep 

 the latter constant. 



Use the following table to convert the degrees of the instrument l^to refrac- 

 tive indexes: 



llHtyro-refractometer and indexes of refraction.* 



"Winton, Conn. Agr. Exper. Stat. Kept., 1900, Part 2, p. 143. 



4. Melting Points of Fats and Fatty Acids, 

 (a) MELTING POINTS OF FATS (WILEY'S METHOD). OFFICIAL. 



(1) PREPARATION OF REAGENTS. 



Place a piece of ice in recently boiled distilled water. Prepare a mixture o> 

 alcohol and water of the same specific gravity as the fat to be examined. 

 This is done by boiling distilled water and 95 per cent alcohol for ten minutes 

 to remove the gases which they may hold in solution. While still hot pour the 

 water into the test tube until it is almost half full. Nearly fill the test tube with 

 the hot alcohol, which is carefully poured down the side of the inclined tube 

 to avoid too much mixing. If the alcohol be not added until the water has 

 cooled, the mixture will contain so many air bubbles as to be unfit for use. 

 These bubbles gather on the disk of fat as the temperature rises and finally 

 force it to the top. 



(2) APPARATUS. 



The apparatus for determining the melting point consists of an accurate 

 thermometer reading easily tenths of a degree ; an ordinary thermometer ; a 

 tall beaker, 35 cm high and 10 cm in diameter ; a test tube, 30 cm long ard 

 3.5 em in diameter ; a stand for supporting the apparatus ; some method of 

 stirring the water in the beaker (for example, a blowing bulb of rubber am* 

 a bent glass tube reaching nearly to the bottom of the beaker). See fig. 6. 



