BILIARY ACIDS. 127 



269. Examine the spectrum of the colored liquid obtained in 

 267. There are two absorption-bands: one at F, the other be- 

 tween D and E, near E. 



270. PREPARATION OF THE FREE BILIARY ACIDS. Dissolve 

 in water some of the sodium salts obtained in 266. Add dilute 

 sulphuric acid slowly, until a precipitate commences to form, 

 then add a little ether. After standing in the cold until the acid 

 has separated, filter, wash, and recrystallize from a small amount 

 of hot water. This gives the glycocholic acid. Examine with the 

 microscope and sketch. 



271. PREPARATION OF CHOLALIC ACID. Add to ox-bile 

 one-fifth of its weight of 30-per-cent. sodium hydrate and boil 

 for twenty-four hours, adding more water to replace that which 

 has evaporated. Then saturate the liquid with carbon dioxid, 

 evaporate to dryness, and extract the mass with strong alcohol. 

 The sodium salt of cholalic acid dissolves, as well as some other 

 sodium compounds. Dilute with water until the solution contains 

 no more than 20 per cent, of alcohol, then precipitate with 

 dilute barium chlorid as long as there is a precipitate. Filter 

 and test the filtrate with barium chlorid, which must give no pre- 

 cipitate. Then precipitate the cholalic acid from this filtrate by 

 decomposing its sodium salt by means of hydrochloric acid. Let 

 it stand several hours until it has become crystalline, then re- 

 crystallize from alcohol. Make sketches of the crystals. 



272. Test the cholalic acid thus obtained with concentrated 

 sulphuric acid, and notice that it gives a green fluorescence. Add 

 a few drops of a cane-sugar solution and see that a red color 

 appears, as with the undecomposed biliary acids. 



273. PREPARATION OF TAUROCHOLIC ACID. The bile of 

 dogs is preferable to ox-bile for this purpose. It contains the 

 sodium salt of the acid. Evaporate the bile to dryness on a 

 water-bath, dissolve in alcohol and precipitate with ether as in 

 266. Dissolve the precipitate in water and precipitate the glyco- 

 cholic acid by the repeated additions of small amounts of ferric 

 chlorid, each time nearly neutralizing the acid reaction with 

 sodium hydrate. Filter and precipitate the iron from the filtrate 

 by an excess of sodium carbonate. Nearly neutralize the filtrate 

 and evaporate to dryness. Dissolve in absolute alcohol, evaporate 

 to dryness and dissolve in water. From this precipitate the 



