t>AlRY PRODUCTS. 67 



and the liquid filtered as before. This process of alternate washings in the flask by 

 agitation with boiling water, followed by cooling, and filtration of the wash-water, 

 is repeated three times, the washings being added to the first filtrate. It is often 

 difficult or impossible to obtain the wash-water wholly free from acid reaction, but 

 when the operation is judged to be complete the washings may be collected separately 

 and titrated with decinormal soda. If the measure of this solution required for neu- 

 tralization does not exceed 0.2cc. further washing of the fatty acids is unnecessary. 



The mixed washings and filtrate are next made up to l,000cc., or some other definite 

 measure, and an aliquot part carefully titrated with decinormal soda (solution c). The 

 volume required is calculated to the whole liquid. The number so obtained repre- 

 sents the measure of decitiormal soda neutralized by the soluble fatty acids of the but- 

 ter fat taken, plus that corresponding to the excess of standard acid used. This last 

 will have been previously ascertained by the blank experiment. The amount of soda 

 employed in this is deducted from the total amount required by the butter fat quan- 

 tity, when the difference is the number of cubic centimeters of standard soda corre- 

 sponding to the soluble fatty acids. This volume multiplied by the factor 0.0088 gives 

 the butyric acid in the weight of butter fat employed. 1 



The flask containing the cake of insoluble fatty acids is thoroughly drained and 

 then placed on the water-bath to melt the contents, which are poured as completely 

 as possible into the (wet) filter, thrtmgh which the aqueous liquid was previously 

 passed. The fatty acids are then washed on the filter with boiling water, to remove 

 the last traces of sparingly soluble acids. The filter is then placed in a small dry 

 beaker and treated in the manner described on page 38, the main quantity of fatty 

 acids and the supplementary portion subsequently dissolved out of the flask and filter 

 being weighed separately. 2 



When it is only required to determine the insoluble acids of butter fat the foregoing 

 tedious mode of operating may be avoided by diluting the soap solution obtained by 

 saponifying 5 grams of the fat till it measures about 300cc. The large excess of alkali 

 is then neutralized by cautious addition of hydrochloric acid, and the hot solution 

 treated with a slight excess of barium chloride or magnesium sulphate. The precip- 

 itated barium or magnesium soap is well washed with hot water, and then rinsed off 

 the filter into a separator, where it is decomposed by dilute hydrochloric acid. The 

 resultant layer of insoluble fatty acids is washed by agitation several times with warm 

 water, and is then treated as directed on page 38. 



In the analysis of butter fat, the sum of the insoluble fatty acids by weight and of 

 the soluble fatty acids, calculated as butyric acid, should always amount to fully 94 

 per cent, of the fat taken. In the author's own experience the sum more frequently 

 approaches or even exceeds 95 per cent., especially if the butter be adulterated. 



The soluble fatty acids, calculated as butyric acid, should amount to at least 5 per 

 cent., any notably smaller proportion being due to adulteration. 3 The insoluble fatty 



1 Thus, suppose an experiment to have given the followiug figures: Weight of butter 

 it taken, 5.120 grams; deciuormal soda required in the blank experiment, 3.90cc. ; 

 jinormal soda required to neutralize one-fifth of the solution of the soluble fatty 

 jids, G.25cc. ; then 



.008 (31.253.9) X 100 



5~Y20 =4.70 per cent. 



8 Instead of weighing the insoluble fatty acids, W. F. Perkins has proposed to dis- 

 >lve them in alcohol, and titrate with standard alkali in the manner described on 

 ige 76. The objection to this plan is the somewhat variable character of the fa^ty 

 acids themselves. Calculating their neutralizing power on the assumption that they 

 are wholly stearic acid, Perkins found 92.0 ami 91.7 per cent, of insoluble acids in 

 pure butter fat. Calculated to oleic acid these figures would not be materially mod- 

 ified, but their equivalents in palmitic acid are 83.3 and 83.0 percent, respectively. 



According to J. Bell, the proportion of soluble acids calculated as butyric acid 

 not unfrequently falls as low as 4.5, and the percentage of insoluble acids sometimes 

 slightly exceeds 89.0. 



