490 PRACTICAL PHYSIOLOGY 



(b) Melt in a crucible with fusion mixture ; after the ash 

 cools, dissolve it in nitric acid and add molybdate of 

 ammonia solution. A yellow precipitate on warming 

 indicates Nuclein. 



If the Biuret Test gives a Rose Pink Colouration, add a few 

 drops of concentrated pure nitric acid. 



A. A white precipitate, which clears up on warming and 



returns on cooling, points to Proteose. Confirm by the 

 salicyl sulphonic acid test (p. 270). 



If proteose be present, saturate some of the original 

 fluid, from which native proteids have been separated 

 by boiling, with sodium chloride. A precipitate indicates 

 primary proteoses. Filter and add a drop of acetic acid; 

 a precipitate points to secondary proteoses. 



B. No precipitate with nitric acid, but a distinct pink biuret 



reaction points to Peptone. Confirm by saturating the 

 original fluid with ammonium sulphate, filtering and 

 applying the biuret test to the filtrate (see p. 172). 

 When two or more Proteids are present, the following method will 

 be found very useful. 



Add a few drops of salicyl sulphonic acid to several c.c. of the 

 original fluid. A white precipitate may indicate native 

 proteid or proteoses. Boil. The proteoses dissolve, 

 whereas the native proteid becomes coagulated. Filter 

 hot. If a precipitate forms in the filtrate on cooling, it 

 indicates Proteoses. Filter off this precipitate and apply 

 the biuret test to the filtrate. A rose pink colouration 

 indicates Peptone. 



III. For Fats. In watery solution fat may be dissolved as a soap. 

 The presence of this can be detected by pouring some of the original 

 fluid into about 20 c.c. of 20 per cent. H 2 S0 4 contained in a small 

 beaker, and heated to near boiling point. If soap be present a film of 

 fatty acid will form on the surface of the fluid. 



IV. The following substances should also be tested for. I. Bile salts 

 Pettenkofer's reaction (p. 233) ; II. Bile Pigments Gmelin's test 

 (p. 234). 



V. Urea (1). Add some fuming nitric to some of the original fluid. 

 Effervescence points to urea. 



(2) Eepeat with hypobromite solution. 



(3) If 1 and 2 be positive, confirm by obtaining urea nitrate crystals. 

 To do this evaporate about 30 c.c. of the original fluid to small bulk, 



