304 CHOLALIC ACID. [BOOK II. 



is set aside, when it becomes crystalline ; it is purified by being 

 recrystallised from its solution in ethyl alcohol, and finally from its 

 solution in methyl alcohol. 



Physical and Cholalic acid may be obtained in the crystalline 

 chemical pro- form, either anhydrous or with one molecule of water 

 perties. of crystallisation. 



From its solutions in ethyl alcohol it separates in the form of 

 colourless, transparent tetrahedra or octahedra, having the com- 

 position C 24 H 40 5 + C 2 H 6 O. Analogous crystalline compounds with 

 methyl and allyl alcohols respectively are obtained when it is 

 crystallised from solutions in these bodies. It also forms compounds 

 with the volatile oils of mustard. 



FIG. 19. CHOLALIC ACID. 



Cholalic acid is very sparingly soluble in cold water requiring 

 4000 times its weight for solution. It is soluble in 750 parts of 

 boiling water ; the acid which separates from the solution on cooling 

 is anhydrous and occurs in microscopic crystals. From solutions in 

 dilute acetic acid, cholalic acid separates in rhombic plates containing 

 one molecule of water of crystallisation. The water of crystallisation 

 is expelled by long continued heating at 100 120 C. The water- 

 free acid melts at 195 C. Cholalic acid is very sparingly soluble 

 in ether; 1000 parts of 70 per cent, alcohol dissolve 48 parts of the 

 acid. It is somewhat soluble in glycerin and in almond oil. 



Solutions of cholalic acid possess the bitter-sweet taste which 

 characterises the conjugated bile acids. Cholalic acid in the free 

 condition, as well as in combination with bases, is dextrogyrous. 



Cholalic acid forms crystalline salts with the alkaline metals, 

 which are readily soluble in water but less so in alcohol. From a 

 watery solution which is not too dilute they are precipitated in 

 a crystalline form by the addition of ether. The sodium salt, 

 C 24 H 39 Na0 5 , has the specific rotation (<z)D = + 31'4. The barium salt 

 (C 24 H 39 5 ) 2 Ba crystallises in silky needles, and is soluble in 30 parts 

 of cold and 23 parts of boiling water ; it is still more soluble in 

 alcohol. The ready solubility of barium cholalate is taken advantage 



