30 



PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



12. DETERMINATION OF MELTING POINTS OF FATS* WILEY'S METHOD." 

 (a) PREPARATION OF REAGENTS. 



Have a piece of ice floating in distilled water that has been recently boiled. Pre- 

 pare a mixture of 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, 

 the water is poured into the test tube described below (2) until it is nearly half 

 full. The test tube is nearly filled with the hot alcohol, which is carefully poured 



down the side of the inclined 

 tube to avoid too much mixing. 

 If the alcohol is not added until 

 the water has cooled, the mix- 

 ture will contain so many air 

 bubbles as to be unfit for use. 

 These bubbles will gather on the 

 disk of fat as the temperature 

 rises and finally force it to the 

 top. 



(b) APPARATUS. 



The apparatus for determin- 

 ing the melting point consists of 

 an accurate thermometer read- 

 ing easily tenths of a degree; a 

 cathetometer for reading the 

 thermometer (but this may be 

 done with an eyeglass if held 

 steadily and properly adjusted) ; 

 an ordinary thermometer; a tall 

 beaker 35 cm high and 10 cm in 

 diameter; a test tube 30 cm long 

 and 3.5 cm in diameter; a stand 

 for supporting the apparatus; 

 some method of stirring the 

 water in the beaker (for example, 

 a blowing bulb of rubber, and a 

 bent glass tube extending to near 

 the bottom of the beaker ) . ( See 

 fig. 2.) 



(c) DETERMINATION. 



w. SCKOLL ai 



FIG. 2. Apparatus for the determination of the melting 

 point. 



The disks of fat are prepared 

 as follows: The melted and fil- 

 tered fat is allowed to fall from 



a dropping tube from a height of from 15 to 20 cm on a smooth piece of ice floating 

 in distilled water that has been recently boiled. The disks thus formed are from 1 

 to 1.5 cm in diameter, and weigh about 200 mg. By pressing the ice under the 

 water the disks are made to float on the surface, whence they are easily removed 

 with a steel spatula, which should be cooled in the ice water before using. 



The disks must be allowed to stand for two or three hours in order to obtain the 

 normal melting point. 



The test tube containing the alcohol and water is placed in a tall beaker contain- 



a See Appendix, p. 151. 



11 F. S. Dept. of Agr., Div. of Chem., Bui. 46 revised, p. 52. 



