DETECTION OF PROXIMATE PRINCIPLES 173 



(c) If the blood is old and dry, and its haemoglobin converted into 

 haeniatin : 



i. Try haemin test. 



ii. Dissolve it in potash ; add ammonium sulphide, and examine for 

 spectrum of haemochromogen. 



11. If bile is suspected : 



(a) Try Gmelin's test for bile pigments (see p. 79). 

 (6) Try Pettenkofer's test for bile salts (see p. 79). 

 (c) Try Hay's sulphur test (see p. 79). 



12. Miscellaneous substances. 



(a) Mucin. Precipitated by acetic acid or by alcohol. The precipitate is 

 soluble in lime water. By collecting the precipitate and boiling it with 25- 

 per-cent. sulphuric acid, a reducing sugar-like substance is obtained. Mucin 

 gives the protein colour tests. 



(b) Nucleo-protein. Precipitated by acetic acid or by alcohol. The pre- 

 cipitate is often viscous. It is soluble in dilute alkalis such as 1-per-cent. 

 sodium carbonate. This solution causes intravascular clotting. If the pre- 

 cipitate is collected and subjected to gastric digestion, an insoluble deposit of 

 nuclein is left, which is rich in phosphorus. Nucleo-protein gives the protein 

 colour tests. 



(c) Gelatin. This also gives some of the proteid colour tests, but not 

 those of Millon or Adamkiewicz. It is not coagulated, but dissolved in hot 

 water. The solution gelatinises when cold. 



(d) Urea. Very soluble in water. The solution effervesces when sodium 

 hypobromite or fuming nitric acid is added. Concentrate a fresh portion, 

 add nitric acid, and examine for crystals of urea nitrate. Solid urea heated 

 in a dry test-tube gives off ammonia, and the residue is called biuret. This 

 gives a rose-red colour with copper sulphate and caustic potash. 



(e) Uric acid. Very insoluble in water ; soluble in potash, and precipitated 

 from this solution in crystals by hydrochloric acid. Uric acid crystals from 

 human urine are deeply pigmented red. Try murexide test (see p. 156). 



(/) Cuolesterin. Characteristic flat crystalline plates. For various colour 

 tests see p. 79. 



13. Urine. Normal constituents 



(a} Chlorides. Acidulate with nitric acid ; add silver nitrate ; white 

 precipitate. 



(6) Sulphates. Acidulate with nitric or hydrochloric acid : add barium 

 chloride ; white precipitate. 



(c) Phosphates. Acidulate with nitric acid ; add ammonium molybdate ; 

 boil ; and a yellow crystalline precipitate forms. To another portion add 

 ammonia ; earthy (i.e. calcium and magnesium) phosphates are precipitated. 



(d) Urea (see above). 



(e) Uric acid. To 100 c.c. of urine add 5 c.c. of hydrochloric acid ; leave 

 for twenty-four hours, and pigmented crystals of uric acid are formed. For 

 tests see above. 



(/) Hippuric acid. Evaporate the urine with nitric acid, and heat the 

 residue in a dry test -tube. A smell of oil of bitter almonds is given off. 



