184 PHYSIOLOGICAL CHEMISTRY 



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. 54, p. 183). 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 temperature at 

 which the fat first begins to melt. This point is indicated by the initial trans- 

 parency. For ordinary fats, raise the temperature very cautiously from 3OC. 

 To determine the congealing-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 con- 

 gealing-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? 



