LARD AND LARB ADULTERATIONS. 



447 



valuable indication. The method pursued in determining this point is 

 as follows : The fatty acids were prepared in sufficient quautities to 

 afford about 50 or 00 grams for analytical purposes. The apparatus 

 used is represented in Fig. 23. 



A very delicate thermometer with a long bulb is used, the thermom- 

 eter being graduated into tenths of a degree; the readings of fche mer- 

 cury are made with a small eye glass. 

 A test tube about 15 cm in length and 

 2.5 to 3 cm in diameter is filled with 

 the melted fatty acids. The tempera- 

 ture at which the acid is melted should 

 be sufficiently high to secure a com- 

 plete liquefaction. The tube contain- 

 ing the fat is placed in a stopper 

 carried in a bottle so that the whole 

 of the fatty acid may be contained in 

 that part of the tube protected from 

 external currents of air by the bottle. 

 The bottom of this protected bottle 

 should be warm, so that its tempera- 

 ture may be several degrees higher 

 than the crystallizing point of the 

 fatty acid. This precaution is neces- 

 sary to avoid a too rapid crystalliza- 

 tion of the fatty acid in the bottom of 

 the test tube and to secure as nearly 

 as possible a uniform crystallization 

 throughout the whole mass. The 

 thermometer is suspended in such a 

 manner that the bulb may occupy as 

 nearly as possible the center of the 

 fatty mass. The thermometer should 

 be protected from currents of air and 

 should be kept perfectly still. The 

 position of the mercury in the ther- 

 mometer is carefully watched by the 

 attendant as it gradually sinks toward 

 the crystallizing point. When the crystals of the acid begin to ap- 

 pear in the bottom and on the sides of the test tube the descent of 

 the mercury will become very slow and finally cease; the lowest 

 point reached by the mercury should be noted. As the crystalliza- 

 tion extends inward toward the bulb of the thermometer a point will 

 be reached when the mercury will begin to rise ; at that point, the test 

 tube being held by the -left hand, the thermometer should be taken by 

 the right hand of the operator and the partially crystallized mass of fat 

 thoroughly stirred by turning the thermometer three or four times 



FIG. 23. 



