46 FOODS AND FOOD ADULTERANTS. 



the disk of fat as the temperature rises and finally force it to the top 

 of the mixture. 



The test tube containing the alcohol and water is placed in a vessel 

 containing cold water, and the whole cooled to below 10 C. The disk 

 of fat is dropped into the tube from the spatula, and at once sinks until 

 it reaches a part of the tu be 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. I n order to secure an even tempera- 

 ture 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. A tube prepared in this way will be suitable for use for sev- 

 eral days, in fact, until the air bubbles begin to attach themselves to the 

 disk of fat. In no case did the two liquids become so thoroughly mixed 

 as to lose the property of holding the disk at a fixed point, even when 

 they were kept for several weeks. 



In practice, owing to the absorption of air, I have found it necessary 

 to prepare new solutions every third or fourth day. 



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

 is slowly heated and kept constantly stirred by means o*f the blowing 

 apparatus already described. 



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

 degrees below the melting point, the disk of fat begins to shrivel, and 

 gradually 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 rotary movement should be given to the thermometer bulb, and 

 I have thought it would be convenient to do this with a kind of clock- 

 work, although I have not carried this idea into execution. The rise of 

 temperature should be so regulated that the last 2 degrees of increment 

 require about ten minutes. The mass of fat gradually approaches the 

 form of a sphere, and when it is sensibly so the reading of the ther- 

 mometer 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 sec- 

 ond tube, containing alcohol and water, is at once placed in the bath. 

 It is not necessary to cool the water in the bath. The test tube (I use 

 ice water 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 about l.5 above the melting point of the fat under exam- 

 ination. 



Working thus with two tubes about three determinations can be made 

 in an hour. 



