66 FOODS AND FOOD ADULTERANTS. 



the stopper under the water aud simultaneously sucking at the syphon. 

 Thus all waiting for the fat to cool is discarded, and reasonable quan- 

 tity of water can be rapidly used to thoroughly wash the fatty acids^ 

 and a filter is not required; 



DETERMINATION OF SOLUBLE AND INSOLUBLE FAT ACIDS. 



METHOD ADOPTED BY ALLEN. 1 



(a). Dissolve 14 grams of good stick-potash in 500cc. of rectified spirit, or methylated 

 spirit which has been redistilled with caustic alkali, and allow the liquid to stand 

 till clear. This solution will be approximately semiuormal. 



(&). A standard hydrochloric or sulphuric acid of approximately semiuormal 

 strength. 



(c). Accurately prepared decinormal caustic soda. Each l.Occ. contains .0040 grams 

 of NaOH and neutralizes, .0088 grams of butyric acid, C^IgO^. 



A quantity of the butter fat (separated from water, curd, and salt, as described on 

 page 152) is melted in a small beaker, a small glass rod introduced, aud (he whole 

 allowed to cool, aud then weighed. It is reinelted, stirred thoroughly, aud about 5 

 grams poured into a strong 6-ounce bottle. The exact weight of fat taken is ascer- 

 tained by reweighing the beaker containing the residual fat. 



By means of a fast-delivering pipette 50cc. measure of the alcoholic potash (solution 

 a), is run into the bottle, and the pipette drained exactly thirty seconds. At the 

 same time another quantity of 50cc. is measured off in an exactly similar manner into 

 an empty flask. 



The bottle is fitted with an india-rubber stopper, which is tightly wired down, and 

 is placed in the water-oven, and from to time removed and agitated, avoiding contact 

 between the liquid and the stopper. In about half an hour the liquid will appear 

 perfectly homogeneous, and when this is the case the saponification is complete, aud 

 the bottle may be removed. When sufficiently cool, the stopper is removed, aud the 

 contents of the bottle rinsed with boiling water into a flask of about 250cc. capacity, 

 which is placed over a steam bath, together with the flask containing merely alco- 

 holic potash, until the alcohol has evaporated. 



Into each of the two flasks is now run about Ice. more semiuormal acid (solution &) 

 than is required to neutralize the potash, and the quantity used accurately noted. 

 The flask containing the decomposed butter fat is nearly tilled with boiling water, 

 a cork with a long upright tube fitted to it, and the whole allowed to stand on the 

 water-bath until the separated fatty acids form a clear stratum on the surface of the 

 liquid. When this occurs the flask and coiiteuts are allowed to become perfectly 

 cold. 



Meanwhile the blank experiment is completed by carefully titrating the contents 

 of the flask with the deciuormal soda, a few drops of an alcoholic solution of phenol- 

 phthalein being added to indicate the point of neutrality. 



The fatty acids having quite solidified, the resultant cake is detached by gently 

 agitating the flask, so as to allow the liquid to be poured out, but avoiding fracture 

 of the cake. The liquid is passed through a filter to catch any flakes of fatty acids* 

 and is collected in a capacious flask. If any genuine butter be contained in the sam- 

 ple, the filtrate will have a marked odor of butyric acid, especially on warming. 



Boiling water is next poured into the flask containing the fatty acids, a cork and 

 long glass tube attached, and the liquid cautiously heated till it begins to boil, when 

 the flask is removed and strongly agitated till the melted fatty acids form a sort of 

 emulsion with the water. When the fatty acids have again separated as an oily layer, 

 the contents of the flask should be thoroughly cooled, the cake of fatty acids detached, 



1 Commercial Organic Analysis, vol. 2, 2d ed., pp. 156 et seq. 



