CHOLESTERIN. PIGMENTS. 129 



acid, then a drop of iodin solution. The crystal becomes 

 first violet, then blue, green, and red. 



279. Dissolve a crystal of cholesterin in a few drops 

 of chloroform in a test-tube, then add an equal volume of 

 concentrated sulphuric acid. The chloroform solution be- 

 comes red, then cherry red, and purple. On pouring it 

 into a dish it becomes blue, green, and finally yellow. 



280. Evaporate on a piece of porcelain a small crys- 

 tal of cholesterin with a drop of concentrated nitric acid. 

 A yellow stain remains which, if treated while warm with 

 ammonia, gives a red color. Too high heating prevents the 

 reaction. 



All these reactions can be employed for the identifica- 

 tion of cholesterin. 



281. PREPARATION OF THE BILIARY PIGMENTS. If 

 biliary calculi are not available, bile may be used for ob- 

 taining bilirubin, employing the yellow or brown in pref- 

 erence to the green. Dilute it with a little water and add 

 a small amount of lime-water, avoiding an excess. Mix 

 by shaking. Pass through the liquid a stream of carbon 

 dioxid to convert any excess into calcium carbonate. Filter 

 out the bilirubin, which has been precipitated as the cal- 

 cium compound, and wash it with water. Suspend the 

 precipitate in water, decompose it with a slight excess of 

 hydrochloric acid, and shake it immediately with a small 

 amount of chloroform to take up the free bilirubin, other- 

 wise it will oxidize to biliverdin. Separate the chloroform 

 solution from the water and precipitate the bilirubin from 

 it by alcohol. 



282. If biliary calculi are at hand they may be used 

 instead of the bile. Pulverize the calculi, then dissolve 

 the cholesterin with a mixture of alcohol and ether. The 

 residue from the alcoholic extraction in the preparation of 



