164 BACTERIOLOGICAL METHODS 



filter, washed twice with cold 90 per cent, alcohol, and dried by suction. After 

 drying by suction they are dried at 100° C. for half an hour and the melting point 

 determined. 



Determination of the Melting Point. — A tube of about i mm. diam., sealed at 

 one end and having a slight flare at the other, is filled to a depth of about s mm. with 

 the dried crystals, which are packed somewhat firmly in the lower end by tapping on 

 a hard surface. This is attached to the bulb of a suitable thermometer and the melt- 

 ing point determined. A thermometer graduated from 95° to 200° C. in one-fifth 

 degrees is used in this laboratory. The determination is made in an Anschutz 

 apparatus, the outer bulb being filled with concentrated sulphuric acid and the inner 

 tube with glycerin. The apparatus is so adjusted that no correction of the observed 

 temperature is required. The melting point of the first crop of crystals usually gives 

 definite information as to the presence or absence of phytosterol, but the conclusion 

 indicated is confirmed by recrystallizing from absolute alcohol and again determining 

 the melting point. If the crystals are pure cholesterol acetate, the melting point of 

 the second crop should agree closely with that of the first. If phytosterol acetate is 

 present, however, a higher melting point should be noted, as phytosterol acetate is 

 less soluble than cholesterol acetate. 



The Emery Method for the Detection of Beef Fat in Lard 



James A. Emery of the Biochemic Division of the Bureau of 

 Animal Industry recommends the following method^ for detect- 

 ing beef fat in lard. It is given here because of its value in isolat- 

 ing the crystals of fats for microscopical examination. 



Technique of Method. — Five grams of the warm filtered fat is weighed (on a bal- 

 ance sensitive to o. i gram) in a glass-stoppered graduated cylinder of 25 cc. capacity, 

 150 to 17s mm. in height, with an internal diameter of about 18 mm., and warm ether 

 is added until the 25 cc. graduation is reached. The glass stopper is securely re- 

 placed and the cylinder is shaken vigorously until complete solution of the fat takes 

 place. The cylinder with its contents is then allowed to stand in a suitable place 

 where a constant temperature, at which it is desired to have the crystallization pro- 

 ceed, may be maintained. (/Vn apparatus described by Rogers proved efficient for 

 the maintenance of this constant temperature.)* After 18 hr. the cylinder is re- 



1 Circular 132, May 23, 1908. Bureau of Animal Industry, U. S. Dept. of 

 Agriculture. 



2 It is necessary to observe great caution in the use of this form of apparatus, as 

 the sparking of the thermo-regulator is a source of danger if the solutions are care- 

 lessly handled. A better form for this work would be one in which the temperature 

 is controlled by a circulating hot-water system heated by a small lamp outside of the 

 box, the regulation of which could be adjusted by using one of the many forms of gas 

 regulators on the market. 



