FATS. 139 



(d) Borax Fusion Test. Fuse a little glycerol on a platinum 

 wire with some powdered borax and note the characteristic green 

 flame. This color is due to the glycerol ester of boric acid. 



(e) Fehling's Test. How does this result compare with the 

 results on the sugars? 



(/) Solution of Cu(OH) 2 . Form a little cupric hydroxide by 

 mixing cupric sulphate and potassium hydroxide. Add a little 

 glycerol to this suspended precipitate and note what occurs. 



12. Melting-Point of Fat. First Method. Insert one of the 

 melting-point tubes, furnished by the instructor, into the liquid fat 

 and draw up the fat until the bulb of the tube is about one-half 

 full of the material. Then fuse one end of the tube in the flame 

 of a bunsen burner and fasten the tube to a thermometer by means 

 of a rubber band in such a manner that the bottom of the fat 

 column is on a level with the bulb of the thermometer (Fig. 39, 

 page 138). Fill a beaker of medium size about two-thirds full of 

 water and place it within a second larger beaker which also contains 

 water, the two vessels being separated by pieces of cork. Immerse 

 the bulb of the thermometer and the attached tube in such a way 

 that the bulb is about midway between the upper and the lower 

 surfaces of the water of the inner beaker. The upper end of the 

 tube being open it must extend above the surface of the surround- 

 ing water. Apply gentle heat, stir the water, and note the tem- 

 perature at which the fat first begins to melt. This point is 

 indicated by the initial transparency. For ordinary fats, raise the 

 temperature very cautiously from 30 C. To determine the con- 

 gealing-point remove the flame and note the temperature at which 

 the fat begins to solidify. Record the melting- and congealing- 

 points of the various fats submitted by the instructor. 



Second Method. Fill a small evaporating dish about one-half 

 full of mercury and place it on a water-bath. Put a small drop 

 of the fat under examination on an ordinary cover glass and place 

 this upon the surface of the mercury. Raise the temperature of 

 the water-bath slowly and by means of a thermometer whose bulb 

 is immersed in the mercury, note the melting-point of the fat. 

 Determine the congealing-point by removing the flame and leaving 

 the fat drop and cover glass in position upon the mercury. How 

 do the melting-points as determined by this method compare with 

 those as determined by the first method? Which method is the 

 more accurate, and why? 



