440 FOODS AND FOOD ADULTERANTS. 



for measuring the temperature of water in the large beaker glass; (3) 

 a tall beaker glass, 35cm high and 10cm in diameter; (4) a test tube 

 3Qcm high and 3.5cm in diameter; (5) a stand for supporting the appa- 

 ratus ; (G) 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; (7) a mixture of alcohol and water of the same 

 specific gravity as the fat to be examined. 



Manipulation. The disks of the fat are prepared as follows: The 

 melted and filtered fat is allowed to fall from a dropping tube from a 

 height of 15 to 20 cm on to a smooth piece of ice floating in water. The 

 disks thus formed are from 1 to 1 cm in diameter and weigh about 

 200 milligrams. 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. 



The mixture of alcohol and water is prepared 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 already described until it is nearly half full. The test tube 

 is then nearly filled with the hot alcohol. It should be poured in gently 

 down the side of the inclined tube to avoid too much mixing. If the 

 tube is not filled until the water has cooled, the mixture 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 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. The disk 

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

 it reaches apart of the tube 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. In ordnr to secure an even temperature 

 in all parts of the alcohol mixture in the vicinity of the disk the ther- 

 mometer is moved from time to time in a circularly, pendulous manner. 

 A tube prepared in this way will be suitable for use for several 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, it has been found neces- 

 sary 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 of the blowing 

 apparatus already described. 



When the temperatu.v of the alcohol-water mixture rises to about 

 C below the melting point the disk of fat begins to shrivel and gradu- 

 ally rolls up into an irregular mass. 



