212 TAUKOCHOLIC ACID. 



purified by recrystallisation from hot water in which they are soluble, 

 separating out again as their solution cools 1 . 



The acid crystallises in fine glistening needles which require about 

 300 parts of cold but only 120 of hot water for their solution. They 

 are also very soluble in alcohol but practically insoluble in ether. The 

 salts of this acid, more especially those with the alkalis, are extremely 

 soluble even in cold water, also in alcohol, but very slightly so if at all 

 in ether. Both the free acid and its salts are dextro-rotatory : for the 

 former, in alcoholic solutions, (a) D = + 29'0, for the latter (a) D = + 25-7 

 (Hoppe-Seyler). Glycocholic acid is a compound of cholalic acid and 

 glycin (glycocoll) or amido-acetic acid. When boiled with hydrolysing 

 agents such as dilute acids or alkalis it takes up one molecule of water 

 and is resolved into its components : 



Glycin. Cholalic acid. 



CjajSO, + H 2 = CH 2 (NH 2 ) COOH + C 24 H 40 5 . 



It is thus analogous in constitution to hippuric acid in which glycin is 

 similarly united to benzoic acid. 



If dissolved in concentrated sulphuric acid and then warmed, glycocholic acid 

 by the removal of one molecule of water yields glycocholonic acid, C 26 H 41 N0 5 . The 

 barium salt of this last acid is insoluble in water, which fact is of importance, since 

 cholonic acid possesses nearly the same specific rotatory power as glycocholic acid. 



4. Taurocholic acid. C 26 H 45 NS0 7 . 



This acid is found to some extent in ox-bile, and is more plentifully 

 present in that of man. The bile of the dog contains taurocholic acid 

 alone, unmixed with glycocholic. 



Preparation. The method described above suffices to obtain 

 glycocholic acid free from taurocholic. On the other hand it is riot 

 by any means easy to obtain the latter free from the former, for 

 taurocholic acid is extremely soluble in water (its crystals are deli- 

 quescent) and this solution can readily dissolve the much less readily 

 soluble glycocholic acid. Hence the mother liquor from the glyco- 

 cholic acid crystals contains not merely the taurocholic acid but some 

 of the former acid also. This difficulty is avoided by employing 

 as a source for its preparation dog-bile in which there is no glyco- 

 cholic acid. The bile is treated as already described down to the 

 stage at which the taurocholate of soda is precipitated from its 

 alcoholic solution by an excess of ether. The precipitate is now 

 dissolved in water and the acid precipitated as a lead salt by the 



1 For details of other methods some special work should be consulted such as 

 Hoppe-Seyler's Handbuch. See also Maly in Hermann's Handbuch d. Physiol. 

 Bd. v. Th. 2, S. 130. Cf. Mylius, Zt. f. physiol Chem. Bd. xi. (1887), S. 231. 



