INSOLUBLE FATTY ACIDS. 257 



50 c.c. of the alcoholic potash solution added, and the flask 

 stoppered and placed in the steam-bath until the fat is saponified 

 completely. The operation may be facilitated by occasional 

 agitation. The alcoholic solution is always measured with the 

 same pipette, and uniformity further secured by allowing it to 

 drain the same length of time (thirty seconds). Two or three 

 blank experiments are conducted at the same time. In from, 

 five to thirty minutes, according to the nature of the fat, the 

 liquid will appear perfectly homogeneous. Saponification being 

 then complete, the flask is removed and cooled. When suffi- 

 ciently cool, the stopper is removed and the contents of the 

 flask rinsed with a little 95 per cent, alcohol into an Erlenmeyer 

 flask of about 200 c.c. capacity, which is placed on the steam- 

 bath, together with the blanks, until the alcohol is evaporated. 

 Titrate the blanks with semi-normal hydrochloric acid. Then 

 run into each of the flasks containing the fatty acids 1 c.c. more 

 of the hydrochloric acid than is required to neutralise the alkali 

 in the blanks. The flask is then connected with a condensing 

 tube, 3 feet long, made of small glass tubing, and heated on 

 the steam-bath until the separated fatty acids form a clear 

 stratum. The flask and contents are then cooled in ice-water. 



The fatty acids having quite solidified, the liquid contents of 

 the flask are poured through a dry filter into a litre flask, care 

 being taken not to break the cake. 



Between 200 and 300 c.c. of water are next brought into 

 the flask, the cork with its condenser tube re-inserted, and the 

 flask heated on the steam-bath until the cake of fatty acids is 

 thoroughly melted. During the melting of the cake of fatty 

 acids, the flask should occasionally be agitated with a revolving 

 motion, but so that its contents are not made to touch the cork. 

 When the fatty acids have again separated into an oily layer, 

 the flask and its contents are cooled in ice-water and the liquid 

 filtered through the same filter into the same litre flask. This 

 treatment with hot water, followed by cooling and filtration of 

 the wash water, is repeated three times, the washings being 

 added to the first filtrate. The mixed washings and filtrates are 

 next made up to 1 litre, aliquot parts titrated with the deci- 

 normal sodium hydroxide, and the total acidity calculated. The 

 number so obtained represents the volume of deci-normal sodium 

 hydroxide neutralised by the soluble acids of the butter fat 

 taken, plus that corresponding to the excess of the standard acid 

 used viz., 1 c.c. The number is, therefore, to be diminished 

 by 5, corresponding to the excess of 1 c.c. of semi-normal acid. 

 This corrected volume, multiplied by 0-0088 gives the weight of 

 (fatty acids calculated as) butyric acid in the amount of butter 

 fat saponified. 



17 



