208 CHOLALIC ACID. 



was first applied by Ginelin 1 and subsequently by Strecker 2 to the 

 acid which is now always known as glycoeholic. The acid now known 

 as taurocholic was originally called 'choleic' by Dernarcay, and the 

 same name has been quite recently used to denote an acid (C 25 H 42 4 ) 

 closely related to cholalic acid (see below). 



This acid occurs in traces as a product of the decomposition of 

 the bile-acids in the small intestine, in larger quantities in the 

 contents of the large intestine, and in the faeces of man and many 

 animals. In icterus the urine is also stated to frequently contain 

 traces of this acid. Its principal interest lies in its being the 

 starting-point, by its union with glycin or taurin, for the acids 

 which, as sodium salts, exist characteristically in bile (see 

 below). 



Owing to the readiness with which ox-bile can be obtained in 

 large quantities, this has been most frequently used for the prep- 

 aration of cholalic acid, whose properties as usually given hence 

 refer to the acid as obtained from this source. More recent re- 

 searches have however demonstrated comparatively unimportant 

 but still distinct differences in the composition and properties of 

 the acid as it occurs in the bile-acids of different animals. The 

 description of the acid which here follows refers to that form 

 which is obtained from ox-bile. 



Preparation. This depends upon the decomposition of the 

 bile-acids (glycocholic and taurocholic) by means of alkalis at 

 boiling temperature. It is not however necessary to employ the 

 purified acids for this purpose since the raw bile suffices. The bile 

 is boiled for twenty-four hours with as much caustic baryta as it 

 will hold in solution, concentration during this operation being 

 avoided by means of a condenser attached to the mouth of the 

 flask. When the decomposition is complete the fluid is filtered 

 while still hot, and the filtrate concentrated until crystals, con- 

 sisting of the barium salt of the acid, are copiously formed. These 

 are then purified by recrystallisation from boiling water and de- 

 composed by the addition of hydrochloric acid. The free cholalic 

 acid is finally obtained in a pure form by solution in a small 

 volume of boiling alcohol from which it separates out in the 

 crystalline form on cooling. 



As thus prepared the acid possesses the following properties. 

 The crystals obtained from hot alcoholic solutions are usually in 

 the form of large rhombic tetrahedra or octahedra, containing 2 

 molecules of water of crystallisation which may be driven off by 

 heating to 100 C. The crystals are but slightly soluble (1 in 

 750) either in water, even when boiling, or in ether, but readily 

 soluble in alcohol. This acid may also be obtained in an amor- 

 phous form by concentrating its solutions to dryness, and is now 



1 Die Verdauung nach Versuchen, 1826. 



2 Liebig's Ann. Bd. LXV. (1848), S. 1. 



