EXAMINATION OF FATS. 1421 



SOLUBLE ACIDS. 



Place the flask on a water bath and evaporate the alcohol. Add 

 such an amount of half-normal hydrochloric acid that its volume plus 

 the amount used in titrating for the saponification number will be 

 1 cc in excess of the amount required to neutralize the 50 cc of alco- 

 holic potash added. Connect the flask with a condensing tube 3 feet 

 long made of small glass tubing and place it on the steam bath until 

 the separated fatty acids form a clear stratum on the upper surface 

 of the liquid. Fill the flask to the neck with hot water and cool 

 it in ice water until the cake of fatty acids is thoroughly hardened. 

 Pour the liquid contents of the flask through a dry, weighed filter into 

 a liter flask, taking care not to break the cake. Fill the flask again 

 with hot water, set on steam bath until the fatty acids collect at the 

 surface, cool by immersing in ice water, and filter the liquid again 

 into the liter flask. Repeat this treatment with hot water, followed 

 by cooling and filtration of the wash water three times, collecting the 

 washings in the liter flask, and titrate with decinormal alkali, using 

 phenolphthalein as indicator. 



The number of cubic centimeters of decinormal alkali used in this 

 titration diminished by 5 (corresponding to the excess of 1 cc of 

 half -normal acid) and multiplied by 0.0088 gives the weight of butyric 

 acid in the amount of fat saponified; dividing this by the weight of fat 

 taken gives the percentage of soluble acids. 



INSOLUBLE ACIDS OR HEHNER NUMBER. 



Allow the flask containing the cake of insoluble acids and the filter 

 paper through which the soluble acids have been filtered to drain and 

 dry for twelve hours in the air. Transfer the filter paper to the flask 

 and dry the flask and contents for three hours in a water- jacketed oven, 

 cool, and weigh. Then dry for another two hours, cool, and weigh. 

 If there be any considerable decrease in weight, repeat the drying. 

 The weight obtained less the weight of the filter paper gives weight 

 of insoluble acids, from which the percentage can be easily calculated. 



DETERMINATION OF FREE FATTY ACIDS. a 



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

 alcohol which has been neutralized with weak caustic soda, using 

 phenolphthalein as indicator, and heat to boiling point. Agitate the 

 flask thoroughly in order to dissolve the free fatty acids as completely 

 as possible. Titrate with decinormal alkali, agitating thoroughly 

 until the pink color persists after vigorous shaking. 



Express results either as percentage of oleic acid, as acid degree 

 (cubic centimeters of normal alkali required to neutralize the free acids 



a Allen, Com. Org. Anal., 3d ed., vol. 2, p. 105. 



