78 ORGANIC CONSTITUENTS. 



The only compound of butyric acid tliat concerns us at present 

 is the butyrate of glycerin, or butyrin, the essential fatty matter 

 of butter. In order to isolate butyrin from the various com- 

 pounds with which it is associated in butter, we must adopt the 

 following method. Purified butter must be kept for some days 

 at a temperature of about 66°. At that temperature olein and 

 butyrin are liquid, while the solid stearin forms a mass by 

 degrees, so that the liquid portion may be decanted off. On 

 this decanted oily matter its own bulk of absolute alcohol must 

 be poured, the mixture must be left for twenty-four hours, and 

 the temperature be regulated to 66°. On distilling off the al- 

 cohol from this alcoholic solution a residue of butyrin is left, 

 mixed with a little olein. A slightly acid reaction is usually ob- 

 served, in consequence of the decomposition of a little of the 

 butjT:'in into butyric acid. This may be removed by digesting 

 the butyrin in a mixture of magnesia and water. A butyrate 

 of magnesia, soluble in water, is formed, and the butyrin may 

 then be obtained perfectly neutral. The removal of all traces 

 of olein from butyrin is nearly impossible. 



Butyrin occurs as a colourless oil, which solidifies at 32°, is 

 soluble in cold alcohol, but not in water, is devoid of odour, 

 and produces no effect on litmus. In a warm atmosphere it 

 speedily decomposes, and yields butyric acid. M M. Pelouze 

 and Gelis have recently shown that by a peculiar process of 

 fermentation butwic acid may be obtained from sugar. They 

 recommend the following as the best process for obtaining the 

 largest possible amount of butyric acid from this source. 



" A small quantity of casein is mixed with a solution of 

 sugar, indicating 10" on the saccharometer, and sufficient chalk 

 to saturate the whole of the butyric acid which subsequently 

 forms. This mixture is left at a constant temperature of from 

 77'^ to 86°. It soon undergoes very considerable alterations ; 

 the fermentation, at first viscous, subsequently lactic, gradually 

 becomes butyric. These decompositions are sometimes successive, 

 sometimes simultaneous, without its being possible to regulate 

 their course. The disengagement of gases becomes more abun- 

 dant, and analyses show that a period arrives when the free 

 hydrogen amounts to a third of the volume of the carbonic 

 acid. At this period the butyric fermentation is in all its 

 vigour ; when at last, at the end of some weeks, all disengage- 



