CHOLIC ACID. 15 



32 atoms carbon, = 24- or per cent. 72*45 



25 atoms hydrogen, = 3-125 9-43 



6 atoms oxygen, =6- 18 '12 



33-125 100-00 



But these atomic constituents differ from those of Dema^ay by 

 five atoms of C H. 



SECTION VIII. OP CHOLIC ACID. 



It has been already mentioned in the last section that bile is a 

 compound of choleic acid and soda. Now, when we boil bile 

 with a fixed alkali, the choleic acid is changed into cholic acid. 

 But it is not easy in this way to obtain cholic acid in any quan- 

 tity. The most convenient method, according to Demarcay, who 

 discovered this acid, is the following.* 



Boil in a capsule equal parts of bile and caustic potash dis- 

 solved in twice its weight of water, adding just water enough to 

 keep the mixture liquid. This boiling process should be con- 

 tinued for some days. The brown clots, which separate by the 

 evaporation of the alkaline liquid, are removed, drained, washed 

 on the filter, and dissolved in water. Acetic acid precipitates 

 from the solution white flocks, which collect on the surface, 

 forming a solid crust, spongy and very friable, if most of the 

 choleic acid has been decomposed ; but if not, the flocks are 

 brown and pitchy, and require to be again treated with potash. 



The precipitate is thrown on a filter, washed, dissolved in al- 

 cohol, and the solution left to spontaneous evaporation. White 

 acicular crystals gradually appear on the surface. They are 

 to be separated by decantation, and washed in cold alcohol. By 

 degrees, the liquid separates into two layers ; the undermost of 

 which has the colour of cashew nut, and is thick and viscid. It 

 is a mixture of choleic and cholic acids. The uppermost is clear 

 and transparent. It is a dilute solution of the two acids. This 

 mixture of the two acids must be again boiled with potash as 

 before. 



The crystals must be dissolved in hot alcohol. By evapora- 

 tion, the acid separates in tetrahedrons. It may be rendered 

 pure by two or three crystallizations from alcoholic solutions. 



The crystals of cholic acid are at first transparent and colour- 



* Ann. de Chim. et de Phys. Ixvii. 200. 



