142 METHODS OF ANALYSIS. 



11. Liquid and Solid Fatty Acids (Muter's Method Modified by Lane*). 



Provisional. 



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

 with lead acetate, and extract with ether, as directed under determination 

 of arachidic acid (p. 145, d). Filter the ether solution of soluble lead soap 

 into a Muter tube or separatory funnel and decompose the soap by shaking 

 with a 40 cc of a 1 : 5 solution of hydrochloric acid. The soap is completely 

 decomposed when the ether becomes clear and colorless. 



Draw off the lead chlorid from the ether solution and wash the ether free 

 from acid. Evaporate an aliquot of this solution until it is free from ether 

 in an atmosphere of carbon dioxid, in order to prevent the oxidation of the 

 oleic acid, and weigh to determine the per cent of liquid acids ; weigh 0.2 to 

 0.3 gram of this and determine the iodin number in the usual way (see 

 page 136). 



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 follow- 

 ing 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 in hot 95 per cent alcohol, transfer to weighed dish, remove the 

 alcohol by evaporation, dry, weigh, and calculate the percentage of soll( 

 fatty acids. 



12. Free Fatty Acids, c Provisional. 



Weigh 20 grams of fat or oil into a flask, add 50 cc of 95 per cent alcol 

 which has been neutralized with weak caustic soda, using phenolphthalein 

 indicator, and heat to the boiling point. Agitate the flask thoroughly in ordt 

 to dissolve the free fatty acids as completely as possible. Titrate with tenth-] 

 normal alkali, agitating thoroughly until the pink color persists after vigoroi 

 shaking. 



Express results either as percentage of oleic acid, as acid degree (cub! 

 centimeters of normal alkali required to neutralize the free acids in 100 grai 

 of oil or fat), or as acid value (milligrams of potassium hydroxid required 

 saturate the free acids in 1 gram of fat or oil). 



1 cc of tenth-normal akali = 0.0282 gram of oleic acid. 



13. Acetyl Value <* Benedikt-Lewkowitsch Method. Provisional. 



Boil the oil or fat with an equal volume of acetic anhydrid for two 

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

 half an hour. To prevent bumping, pass a slow current of carbonic a< 

 into the liquid through a finely drawn out tube reaching nearly to the botl 

 Allow the mixture to separate into two layers, siphon off the water, and 

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



Separate the acetylated fat from the water and dry and filter in a dryii 

 oven. 



Muter and De Konlngh, Analyst, 1889, 14: 61. 

 6 J. Amer. Chem. Soc., 1893, 15 : 110. 

 r Allen, Commercial Organic Analysis, 3d ed., 2: 105. 



* Lewkowitsch, J. Soc. Chem. Ind., 1897, 16: 503; Benedikt, Analyse der Fette 

 Wachsarten, 3d ed., p. 146; Allen, Commercial Organic Analysis, 3d ed., 2 (1): 66. 



