328 BUTTBE. 



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. 



The flask containing the cake of insoluble acids and the paper 

 through which the soluble acids were filtered are allowed to 

 drain and dry for twelve hours, when the cake, together with as 

 much of the acids as can be removed from the filter paper, is 

 transferred to a weighed glass dish. . The funnel and filter are 

 then set in an Erlenmeyer flask and the filter washed thoroughly 

 with absolute alcohol. The flask is rinsed with the washings 

 from the filter paper, then with pure alcohol, and these trans- 

 ferred to the glass dish, which is placed in the steam-bath. After 

 the alcohol has evaporated, the residue is dried for two hours 

 in an air-bath at 100° C, cooled in a desiccator, and weighed. 

 It is heated in the air-bath for two hours more, cooled and weighed. 

 If the two weighings are decidedly different, a further heating 

 for two hours must be made. The residue is the total insoluble 

 acids of the sample. 



This method has been submitted to numerous modifications ; 

 Hager proposes to add a known weight of wax, picks out the lump, 

 dries, and weighs it. Fleischmann and Vieth advise that the wash- 

 ing should be continued till at-each succeeding washing the colora- 

 tion produced by the addition of a few drops of litmus solution 

 to a few cubic centimetres of the filtrate is not changed. Cassal 

 has devised an ingenious flask, which has a tap at the bottom so 

 that the liquid can be run off, leaving the fatty acids in the 

 flask ; washing can be thus much expedited, as hot water can be 

 added, the fatty acids shaken up with the water, and the water 

 run off. 



The variation of insoluble fatty acids is from 85 '5 per cent. 

 (Bell and Menozzi) to 90'0 per cent. (Reichardt, Cornwall, and 

 others) in genuine butters ; the soluble fatty acids calculated as 

 butyric vary from 7'0 per cent, to 4'0 per cent. Most other fats 

 give about 95 '5 per cent, of insoluble fatty acids and traces only 

 of soluble fatty acids. Coco-nut and palm-nut oils are, how- 

 ever, exceptions to this, yielding from 82 to 85 per cent. 



Estimation of the Mean Combining "Weight of the 

 Insoluble Patty Acids. — The fatty acids are dissolved in 

 alcohol, a little phenolphthalein added, and titrated with alcoholic 

 alkali ; when a pink colour is obtained a small excess is added 

 (2 or 3 c.c), the solution heated to boiling for ten minutes, and 

 the excess titrated back, as in the Koettstorfer process. 



The mean combining weight of the fatty acids is calculated as 

 the saponification equivalent. Direct titration of the fatty acids 



