EDIBLE OILS AND FATS. 27 



from number of cubic centimeters necessary to neutralize the 50 cc of alkali added, 

 multiplying the result by 28.06 (mg. potassium hydroxid per cubic centimeter) and 

 dividing by the number of grams of fat used. 



To calculate the saponification equivalent a divide 56,100 by the saponification 

 number, the saponification equivalent being the number of grams of fat saponified 

 by one equivalent of potassium hydroxid, or 56.1 grams. There is no advantage in 

 stating it in this way, and for sake of uniformity, the Koetstorfer number being more 

 generally used, it would seem advisable to adopt it. 



(d) 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 saponiiication number will be 1 cubic centimeter in excess of the amount 

 required to neutralize the 50 cc of alcoholic 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 deci-normal alkali, using phenolphthalein as indicator. 



The number of cubic centimeters of deci-normal alkali used in this titration dimin- 

 ished 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. 



(e) 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. 



6. DETERMINATION OF FREE FATTY ACIDS. b 



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, 

 ui id heat to boiling point. Agitate the flask thoroughly in order to dissolve the free 

 fatty acids as completely as possible. Titrate with deci-normal 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 ivi|iiirvd to neutralize the free acids in 100 grams of oil or fat), or as 

 acid value (milligrams of potassium hydroxid required to saturate the free acids in 

 1 gram of fat or oil). 



1 cc deci-normal alkali =0.0282 grams oleic acid. 



7. DETERMINATION OF VOLATILE ACIDS OR REfcHERT-MEissL NCMHKK. 

 Sec methods for dairy products p. 38. 



'Allen, Com. Org. Anal., 3d ed., vol. 4 2, pt. 1. pp. 

 ' Allen, Coin. Ortf. Anal., M !.. vol. '2, p. 10V 



