Conditions Affecting Butter-Fat. 449 



margarine, or between genuine butter and mixtures of butter 

 and margarine. The following is a summary of the essential 

 features of the methods, some or all of which are usually followed 

 by the analyst in his examination of samples of butter : — 



(1) Determination of Soluble and Insoluble Acids. — In this pro- 

 cess a small quantity of the butter-fat, separated from water and 

 curd, is saponified by heating with an alcoholic solution of potash. 

 By this treatment the fatty acids of the glycerides are liberated 

 from their combination with the glycerin, and combine with the 

 alkali to form a soap. From this soap, dissolved in hot water, 

 they are set free by the addition of sulphuric acid, and on 

 cooling the mixture, the " insoluble fatty acids " are obtained as 

 a solid cake upon the surface of the liquid, whilst in the latter 

 the "soluble fatty acids" remain dissolved. The insoluble acids 

 are separated from the liquid by filtration, washed with water 

 to remove adherent soluble acids, dried, and weighed. The 

 quantity of insoluble acids thus obtained, expressed as a per- 

 centage of the butter-fat, is usually referred to as the " Hehner 

 value" of the butter, and in normal samples may range from 

 about 86£ to 89. In margarine the value is about 95. 



The soluble acids are contained in the liquid which has been 

 filtered from the cake of insoluble acids. In order to ascertain 

 their amount this acid liquid is neutralised with a standard 

 solution of alkali, of which the volume required is carefully noted. 

 The quantity of standard alkali used, after being corrected for 

 the known amounts of potash and sulphuric acid employed in 

 the earlier stages of the experiment, is a measure of the soluble 

 acids in the liquid, and the weight of these acids can be at once 

 calculated from the result obtained. As a rule the soluble acids 

 are from about 4^ to 7 per cent, of the butter-fat, whereas in 

 margarine the figures are much lower, and usually less than 

 1 per cent. 



(2) Volatile Fatty Acids. — In determining the amount of these 

 acids the butter-fat is first saponified and treated with sulphuric 

 acid, as already described for the insoluble acids. Mixed with 

 water in a flask, the free fatty acids thus obtained are distilled, 

 and the volatile members are in this way separated from the 



fixed " or non-volatile acids. They are collected, together with 

 the condensed steam, in a receiver, filtered from such small 



K K 



