ANALYSIS OF BUTTER-FAT. 43 



On the addition of a strong mineral acid, such as sulphuric 

 acid, to the soap obtained by the action of the alkali, the 

 fatty acids are liberated, sulphate of potash being formed. 

 Thus are obtained, partly in solution, partly as precipitate, 

 sulphate of potash, glycerin, fatty acid, and excess of mineral 

 acid. Some of the fat acids, as oleic, palmitic, and stearic acids, 

 are, as we have shown in Chapter I., insoluble in water, whilst 

 others, such as butyric, caproic, etc., are soluble in the same 

 menstruum ; the soluble acids possess, moreover, the property 

 of being volatile, and, to distil from their aqueous solution 

 without decomposition ; their solubility decreases as the num- 

 ber of carbon atoms they contain increases, and the volatility 

 stands in a similar relation to their composition. Hence in the 

 case of fatty acids, soluble and volatile are synonymous terms. 

 The simplest plan, which seemed to allow of an accurate, 

 quantitative determination, in butter-fat of the acids, which 

 we comprise under the name of butyric, appeared to be to 

 saponify the fat, to decompose the soap by means of dilute 

 sulphuric acid, and to subject the mixture containing the 

 free acids to distillation. The volatile acids would thus be 

 found in the distillate. This process had been applied 

 many years ago by Chevreul, who thus prepared butyric acid 

 from butter. A quantitative determination seems, however, 

 never to have been made. 



The following experiments were undertaken with this view : 

 Experiment 1. A weighed quantity of the fat of genuine 

 butter was saponified by means of caustic potash in 

 a boiling flask. The saponification presented many diffi- 

 culties, since the oil floats on the top, and is but slowly 

 decomposed by the alkaline solution, which, under such cir- 

 cumstances, boils most irregularly and violently, so as either 

 to break the flask or to cause the liquid to run over. After 

 many unsuccessful experiments we at last obtained a perfectly 

 bright and clear yellowish soap, which gelatinised on cooling. 



