28 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



8. FOR ESTIMATION OF LIQUID AND SOLID FATTY ACIDS, MUTER' s METHOD a MODI- 

 FIED BY LANE. b 



Weigh 5 grams of oil or fat into an Erlenineyer flask, saponify, precipitate with 

 lead acetate, and extract with ether, as directed under determination of arachidic acid. 

 Filter the ether solution of soluble lead soap into a Muter tube or separatory fun- 

 nel and decompose the soap by shaking with 40 cc of a 1 : 5 solution of hydrochloric 

 acid. The soap is completely decomposed when the ether becomes clear and colorless. 



The lead chlorid is drawn off from the ether solution and the ether washed free 

 from acid. An aliquot of this ether solution is evaporated free from ether in an 

 atmosphere of carbon dioxid in order to prevent the oxidation of the oleic acid, and 

 weighed to determine the per cent of liquid acids; .2 to .3 gram of this is weighed 

 and the iodin number determined in the ordinary way. 



As it is very difficult to dry the oleic acid without very serious oxidation, it is just 

 as satisfactory to determine the weight of insoluble acids by the following method: 

 Wash the insoluble soap left on the filter into a flask, decompose with hydro- 

 chloric acid, and heat until the fatty acids are melted. Fill the flask with hot water, 

 cool, pour off the water, and wash again the solidified fatty acids. Dissolve them in 

 hot 95 per cent alcohol, transfer to weighed dish, remove the alcohol by evaporation, 

 dry, weigh, and calculate the percentage of solid fatty acids. 



9. DETERMINATION OF ACETYL VALUE. C 



Benedikt proposed to determine the hydroxy acids and" alcohols by the use of 

 acetic anhydrid (C 2 H 3 O) 2 as illustrated in the following reaction : d 



C 17 H 32 (OH)COOH-f(C 2 H 3 0) 2 0=C 17 H 32 (OC 2 H 3 0)COOH+HC 2 H 3 2 



He proposed to work on the fatty acids, but the process was modified by Lewko- 

 witsch e who works on the oils or fats directly, which gives more exactly the true 

 content of hydroxy acids. f 



The procedure is as follows: 



Boil the oil or fat with an equal volume of acetic anhydrid (C 2 H 3 O) 2 O for two 

 hours and pour the mixture into a large beaker containing 500 cc of water and boil 

 for half an hour. To prevent bumping, a slow current of carbonic acid is passed into 

 the liquid through a finely drawn out tube reaching nearly to the bottom. Allow 

 the mixture to separate into two layers, siphon off the water, and boil the oily layer 

 with fresh water until it is no longer acid to litmus paper. 



The acetylated fat is then separated from the water and dried and filtered in a 

 drying oven. 



Weigh from 2 to 4 grams of the acetylated fats into a flask and saponify with 

 alcoholic potash as in the determination of saponification equavalent. If the distil- 

 lation process is to be adopted it is not necessary to work with a standardized alco- 

 holic potash solution. In case the filtration method is used, which will be found 

 much shorter, it is necessary that the alcoholic potash should be measured exactly. 



In either case evaporate the alcohol after saponification and dissolve the soap in 

 water. Now two procedures are possible either distillation or filtration. 



(a) DISTILLATION PROCESS. 



Acidify with dilute sulphuric acid (1-10) and distill the liquid as in the Reichert 

 test. As several hundred cubic centimeters must be distilled, either a current of 



J. Muter and L. L. De Koningh, Analyst, 1889, 14, 61. 

 ' X. J. Lane, Jour. Am. Chem. Soc., 1893, 15, 110. 



c Lewkowitsch, Jour. Soc. Chem. Ind., 1897, 16, 503-506; Benedikt, Analyse der Fette u. Wach, 3d ed., 

 p. 146; Allen, Com. Org. Anal., 3d ed., 2, pt. 1, pp. 66-67. 

 (1 Benedikt and Lewkowitsch, Oils, Fats, and Waxes, p. 127. 

 .lour. S.>c. ('In-ill. Ind., 1897, 16, 503. 

 f J. Lewkowitsch, Jour. Soc. Chem. Ind., 1890, 9, 846. 



