146 METHODS OF ANALYSIS. 



flask has cooled, the water and excess of lead can be poured off and the soap 

 washed with cold water and with 90 per cent (by volume) alcohol. Add 200 cc 

 of ether, cork, and allow to stand for some time until the soap is disintegrated ; 

 heat on the water bath, using a reflux condenser, and boil for about five minutes.** 

 In the oils most of the soap will be dissolved, while in lards, which contain much 

 stearin, part will be left undissolved. Cool the ether solution of soap to from 

 15 to 17 C. and let stand until all the insoluble soaps have crystallized out 

 (about twelve hours). 



Filter and thoroughly wash the precipitate with ether. Save the filtrate for 

 the determination of the iodin number of the liquid fatty acids by the Muter 

 method (page 142). Wash the soaps on the filter back into the flask by means of 

 a stream of hot water acidified with hydrochloric acid. Add an excess of dilute 

 hydrochloric acid, partially fill the flask with hot water, and heat until fatty 

 acids form a clear oily layer. -Fill the flask with hot water, allow the fatty 

 acids to harden and separate from the precipitated lead chlorid, wash, drain, 

 repeat washing with hot water, and dissolve the fatty acids in 100 cc of 

 boiling 90 per cent by volume alcohol. Cool to 15 C., shaking thoroughly to 

 aid crystallization. 



From 5 to 10 per cent of peanut oil can be detected by this method, as it 

 effects a complete separation of the soluble acids from the insoluble, which 

 interfere with the crystallization of the arachidic acid. Filter, wash the precipi- 

 tate twice with 10 cc of 90 per cent by volume alcohol, and then with alcohol 70 

 per cent by volume. Dissolve off the filter with boiling absolute alcohol, evapo- 

 rate to dryness in a weighed dish, dry, and weigh. Add to this weight 0.0025 

 gram for each 10 cc of 90 per cent alcohol used in the crystallization and wash- 

 ing if done at 15 C. ; if done at 20? add 0.0045 gram for each 10 cc. The melting 

 point of arachidic acid thus obtained is between 71 and 72 C. Twenty times 

 the weight of arachidic acid will give the approximate amount of peanut oil 

 present. No examination for adulterants in olive oil is complete without making 

 the test for peanut oil. Arachidic acid has a characteristic structure and can 

 be detected by the microscope. 



(e) BAUDOUIN TEST FOR SESAME OIL. PROVISIONAL. 



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

 gf. 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. In the presence 

 of even a very small admixture of sesame oil this is colored crimson. Some 

 olive oils give a slight pink coloration with this reagent, but they are not hard 

 to distinguish if comparative tests with sesame oil are made. 



(f ) VILLA VECCHIA & TEST FOR SESAME OIL. PROVISIONAL. 



Add 2 grams of furfural to 100 cc of alcohol (95 per cent) and mix thoroughly 

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

 oil by shaking them together in a test tube. The same color is developed as 

 when sugar is used, as in the Baudouin test. 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. 



Process used by N. .T. Lane In his modification of Muter's method ; J. Amer. Chem. Soc., 

 1893, 18: 110. 



6 Villavecchia and Fabrls, J. Soc. Chem. Ind., 1893, 12: 67; 1894, 13: 69. Benedikt 

 and Lewkowltscb, Oils, Fats, and Waxes, p. 385. 



