192 THE URINE. 



402. In urine which is highly colored with other substances 

 the bilirtibin may be identified by Stokvis's test. To 20 or 30 

 cubic centimeters of urine in a test-tube add 5 or 10 cubic centi- 

 meters of a 20-per-cent. solution of zinc acetate. Wash the pre- 

 cipitated bilirubin upon a small filter; then dissolve it by the 

 addition of a few drops of ammonia. The liquid which passes 

 through the filter becomes, after standing, brownish green, and 

 shows the spectrum of bilicyanin: an absorption-band between G 

 and D and one between D and E. If much bile is present the 

 liquid becomes blue upon slightly acidifying. 



403. To the urine add a few drops of very dilute tincture of 

 iodin. A green color results. If the iodin is flowed on to the 

 top of the urine by slanting the tube or by dropping from a 

 pipette a green ring is formed. 



404. Test the biliary urine for biliary acids by dis- 

 solving in it a few crystals of cane-sugar, then dipping in 

 it a strip of filter-paper. Dry the paper and place on it 

 a drop of concentrated sulphuric acid. In a few seconds 

 it becomes violet, best seen by holding it before a window. 

 Too much sugar gives a brown color. 



405. Instead of using concentrated acid make the 

 test with dilute H 2 S0 47 as in Experiment 268. 



It is not advisable to depend upon Pettenkofer's test alone in 

 the urine, as other substances may be present and give reactions 

 similar to those of the bile-acids, although their spectra are differ- 

 ent. The pure bile-acids may, in cases of doubt, be extracted by 

 the following method: 



406. If the urine is highly colored or only a slight amount 

 of bile-acids are present, it may be necessary to extract the latter 

 before testing. Add to the urine lead acetate solution and a few 

 drops of ammonia to make it slightly alkaline. Wash with 

 water the precipitate, which contains the acids, then dry it. Ex- 

 tract it several times with warm alcohol, filtering hot. Make the 

 filtrate alkaline with sodium carbonate, and evaporate to dryness 

 on a water -bath. Dissolve the sodium salts of the bile-acids from 

 the residue with hot, strong alcohol and filter. The bile-salts can 



