314 METHODS OF ANALYSIS [Chap. 



Distil the ether from the solution of insoluble fatty acids and dry the latter in the 

 flask by adding a little absolute alcohol and evaporating on a steam bath. Dissolve 

 the dry fatty acids by warming with 100 cc. of 90% alcohol by volume and cool 

 slowly to 15°C., shaking to aid crystallization. Allow to stand at 15°C. for 30 

 minutes. In the presence of peanut oil, crystals of arachidic acid will separate from 

 the solution. Filter, wash the precipitate twice with 10 cc. of 90% alcohol by 

 volume, and then with 70% alcohol by volume, care being taken to maintain the 

 arachidic acid and the wash solutions at a definite temperature in order to apply 

 the solubility corrections given below. Dissolve the arachidic acid upon the filter 

 with boiling absolute alcohol, evaporate to dryness in a weighed dish, dry and 

 weigh. Add to the weight 0.0025 gram for each 10 cc. of 90% alcohol used in the 

 crystallization and washing, if conducted at 15°C.; if conducted at 20°C., add 0.0045 

 gram for each 10 cc. The melting point of arachidic acid thus obtained is 71°- 

 72°C. Twenty times the weight of arachidic acid will give the approximate amount 

 of peanut oil present. Arachidic acid has a characteristic appearance and may 

 be identified by the microscope. As little as 5-10% of peanut oil can be detected 

 by this method. 



SESAME OIL. 



38 Baudoin Test. — Official. 



Dissolve 0.1 gram of finely powdered sugar in 10 cc. of hydrochloric acid (sp. 

 gr. 1.20), add 20 cc. of the oil to be tested, shake thoroughly for a minute and allow 

 to stand. The aqueous solution separates almost at once and, in the presence of 

 even a very small admixture of sesame oil, is colored crimson. Some olive oils 

 give a slight pink coloration with this reagent. Comparative tests with known 

 samples containing sesame oil will differentiate them. 



39 Villavecchia Test^^.— Official. 



Add 2 grams of furfural to 100 cc. of 95% alcohol by volume and mix thoroughly 

 0.1 cc. of this solution, 10 cc. of hydrochloric acid (sp. gr. 1.20), and 10 cc. of the oil 

 by shaking them together in a test tube. A crimson color is developed as in the 

 Baudoin test, 38, where sugar is used. 



Villavecchia explained this reaction on the basis that furfural is formed by the 

 action of levulose and hydrochloric acid and therefore substituted furfural for 

 sucrose. As furfural gives a violet tint with hydrochloric acid it is necessary to use 

 the very dilute solution specified in the method. 



BEEF FAT IN LARD. 



40 Emery Method^°. —Tentative. 



Weigh 5 grams of the melted fat into a glass-stoppered 25 cc. cylinder about 

 150-175 mm. in height. Add warm ether up to the 25 cc. mark, stopper securely 

 and shake until the fat is completely dissolved. Allow the cylinder to stand for 

 about 18 hours at a temperature of 16°-20°C. during which time some of the solid 

 glycerides will crystallize out. Decant the clear solution carefully from the crys- 

 tals, wash with three 5 cc. portions of cold ether, avoiding breaking up the deposit 

 during the first 2 washings. Agitate the crystals with the third portion of ether 

 and transfer to a small filter. Wash on the paper with successive small amounts 

 of cold ether until 15-20 cc. have been used, then remove the last traces of ether by 

 means of slight suction on the stem of the funnel. Break up any large lumps and 

 allow the deposit to dry. 



