34 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



be dissolved, while in lards, where there is so much stearin, part will be left undis- 

 solved. Cool the ether solution of soap down to from 15 to 17 C., and allow to 

 stand until all the insoluble soaps have, crystallized out. It should stand about 

 twelve hours. 



Now, filter and wash the precipitate with* ether. Save the filtrate for the deter- 

 mination of the iodin number of the liquid fatty acids by the Muter method. 

 * The soaps on the filter are washed back into the flask by means of a stream of hot 

 water acidified with hydrochloric acid. 



Add an excess -of dilute hydrochloric acid, fill up the flask with hot water, allow 

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

 drain, and dissolve the fatty acids in 25 cc of boiling 90 per cent (by volume) alcohol. 

 The crystals of arachidic acid separate out as the liquid cools. 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 

 arai'hidic acid. Filter, wash the precipitate twice with 10 cc of 90 per cent (by volume) 

 alcohol, and then with alcohol of 70 per cent (by volume). Dissolve off the filter 

 with boiling absolute alcohol, evaporate 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 washing if done at 15 C., if done at 20, 0.0045 gram for each 

 10 cc. 



The melting point of arachidic acid obtained in this way is between 71 and 72 C. 

 Twenty times the weight of arachidic acid will give the approximate amount of 

 peanut oil present. 



Another method a which gives as satisfactory an approximation of the amount of 

 peanut oil present is to allow the arachidic b acid to crystallize in a 100 cc graduated 

 cylinder and measuring the volume of the precipitate. This volume will have to be 

 determined for the working temperature and the length of the time by use of known 

 mixtures of peanut oil. Cotton-seed and lard oil give slight precipitates when 

 treated by this method. 



Arachidic acid has a characteristic structure and can be detected by the microscope. 



No examination of olive oil is complete without making the test for peanut oil, 

 which is probably a common adulterant, especially in French and Italian oils. 



19. BAUDOUIN TEST FOR SESAME OIL. 



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. 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. 



20. VILLIVECCHIA c TEST FOR SESAME OIL. 



Mix 2 grams of furfurol with 100 cc alcohol (95 per cent), and take 0.1 cc of this 

 solution, 10 cc hydrochloric acic (sp. gr. 1.20), and 10 cc of oil and mix thoroughly 

 by shaking in a test tube and the same color is developed as when the sugar is used. 

 Villivecchia attributed the Baudouin test to the formation of furfurol from the action 

 of levulose and hydrochloric acid, and so substituted furfurol for sucrose. 



As furfurol and hydrochloric acid give a violet tint with hydrochloric acid, it is 

 necessary to use the very dilute solution given in the method. 



Suggested by W. D. Bigelow. 



b As the solubility of arachidic acid in 90 per cent alcohol increases very rapidly with the tempera- 

 ture, care must be taken to keep the temperature of crystallization down to between 15 and 20 C., 

 and to obtain satisfactory results the temperature must be same as used in the standards. 



= Villivecchia and Pabris, Journ. Soc. Chem. Ind., 1893, 12, 97 and 1894, 13, 69. Benedikt and Lew- 

 kowitsch. Oils, Fats, and Waxes, p. 318. 



