1U CHEMICAL PHYSIOLOGY. 



green colour, and it froths very easily when shaken. Filter- 

 paper dipped into it gives a yellow stain on drying. 



(b.) Gmelin's Test (Nitric acid containing nitrous acid). 

 (1) Place a few drops of the suspected urine on a white por- 

 celain plate, and near it a few drops of the impure nitric acid; 

 let the fluids run together and the usual play of colours is 

 observed (Lesson IX., 6). (2) Take urine in a test-tube, pour 

 in the impure HNO 3 , until it forms a stratum at the bottom ; 

 if bile-pigments be present, at the line of junction of the 

 fluids a play of colours takes place from above downwards 

 green, blue, violet or dirty red, and yellow. Nearly all 

 urines give a play of colours, but green is the necessary and 

 characteristic colour to prove the presence of bile-pigments. 

 Or (3) filter the urine several times through the same 

 filter, dry the filter-paper, and to it apply the impure nitric 

 acid, when the same play of colours is observed. 



(c.) A solution of methyl-violet poured on icteric urine 

 by the contact method gives a bright carmine ring at the 

 point of contact. 



(d.) If much bile-pigment be present, the following test 

 succeeds : Mix the urine with caustic potash (1 KHO to 3 

 water), and add hydrochloric acid. The fluid becomes green, 

 due to the formation of biliverdin. 



B. Bile-Acids (Glyco-cholic, and Tauro-cholic acids). 



(a.) Pettenkofer's Test. Add to urine a few drops of syrup 

 of cane sugar (8 per cent.), mix them, and pour strong 

 sulphuric acid down the side of the tube until it forms a 

 layer at the bottom. The temperature must not rise above 

 70 C., nor must the urine contain albumin. At the line of 

 junction a cherry-red or purple-violet colour indicates the pre- 

 sence of the bile-acids. Or proceed as follows : Shake the 

 tube with the urine and the syrup to get a froth, and when 

 the sulphuric acid is added, the froth shows the colour. 

 N.B. The test in this simple form often fails with urine, 

 and in fact there is no satisfactory simple test for minute 

 quantities of these acids in urine. 



(b.) Strasburg's Modification. Dissolve cane sugar in the 

 suspected urine, dip into it filter-paper, and allow it to dry. 

 Touch the paper with a glass rod dipped in strong sulphuric 



