LARD AND LARD ADULTERATIONS. 441 



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, which 

 might be done with a kind of clock-work. The rise of temperature 

 should be so regulated that the last 2 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 thermometer 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 second 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 (ice- water being used 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 1.5 above 

 the meltuig point of the fat under examination. 



Working thus with two tubes about three determinations can be made 

 in an hour. After the test tube has been cooled the globule of fat is 

 removed with a small spoon attached to a wire before another disk of 

 fat is put in. 



(d) Refractive index. The apparatus used in determining the refrac- 

 tive index is one described by Professor Abbe in a brochure entitled 

 " Neue Apparatezur Bestimmung des Brechungs-nnd Zcrstreuungsver- 

 mngen fester und fliissiger Korper." 'The apparatus is represented 

 in Fig. 21. For lard it is necessary that the index of refraction be de- 



termined in a room where the temperature is higher than 30 and even 

 higher than 35. For determining the refractive index of oleo-stearines 

 the temperature must be considerably above 40. For very high tern- 



