264 



PHYSIOLOGICAL CHEMISTRY 



Filter. The filtrate should be clear and the coagulum dark brown. Reserve 

 this coagulum. What body gives the coagulum this color? Evaporate the 

 filtrate to about 25 c.c., filtering off any precipitate which may form in the process. 

 Make the following tests upon the filtrate : 



(a) Fehling's Test To 5 c.c. of the neutralized filtrate add 5 drops of Feh- 

 ling's solution and boil one minute. 



(b) Chlorides. To a small amount of the filtrate in a test-tube add a few 

 drops of nitric acid and a little silver nitrate. In the presence of chloride, a white 

 precipitate of silver chloride will form. 



(c) Phosphates. Test for phosphates by nitric acid and molybdate solution 

 according to directions given on page 58. 



(d) Crystallization of Sodium Chloride. Place the remainder of the filtrate 

 in a watch glass and evaporate it on a water-bath. Examine the crystals under 

 the microscope and compare them with those in Fig. 86, page 269. 



6. Test for Iron. Incinerate a small portion of the coagulum from the last 

 experiment (5) in a porcelain crucible. Cool, dissolve the residue in dilute hy- 

 drochloric acid and test for iron by potassium ferrocyanide or ammonium thio- 

 cyanate. Which of the constituents of the blood contains the iron? 



FIG. 83. EFFECT OF WATER ON ERYTHROCYTES. 



7. Hemolysis ("Laky Blood"). Note the opacity of ordinary defibrinated 

 blood. Place a few cubic centimeters of this blood in a test-tube and add water, 

 a little at a time, until the blood is rendered transparent. Hemolysis has taken 

 place. How does the water act in causing this transparency? Examine a drop 

 of hemolyzed blood under the microscope. How does its microscopical appear- 

 ance differ from that of unaltered blood? What other agents may be used to 

 bring about hemolysis? 



8. Osmotic Pressure. Place a few cubic centimeters of blood in each of 

 three test-tubes. Hemolyze the blood in the first tube according to directions 

 given in the last experiment (7) : add an equal volume of isotonic (0.9 per cent) 

 sodium chloride to the blood in the second tube, and an equal volume of 10 per 

 cent sodium chloride to the blood in the third tube. Mix thoroughly by shaking 

 and after a few moments examine a drop from each of the three tutfes under the 



