210 



PHYSIOLOGICAL CHEMISTRY 



8. Tests for Cholesterol. 



(a) Microscopical Examination. Examine the crystals under the microscope 

 and compare them with those shown in Fig. 57, below. 



(b) Sulphuric Acid Test (Salkowski). Dissolve a few crystals of cholesterol 

 hi a little chloroform and add an equal volume of concentrated sulphuric acid. 

 A play of colors from bluish-red to cherry-red and purple is noted in the chloro- 

 form while the acid assumes a marked green fluorescence. 



(c) Acetic Anhydride-H 2 SO4 Test (Liebermann-Burchard). Dissolve a 

 few crystals of cholesterol in 2 c.c. of chloroform in a dry test-tube. Now add 10 

 drops of acetic anhydride and 1-3 drops of concentrated sulphuric acid. The 

 solution becomes red, then blue, and finally bluish-green in color. This reaction 

 is used in the quantitative determination of cholesterol (see Chapter XVI). 



(d) Iodine-sulphuric Acid Test. Place a few crystals of cholesterol in one of 

 the depressions of a test-tablet and treat with a drop of concentrated sulphuric acid 

 and a drop of a very dilute solution of iodine. A play of colors consisting of violet, 

 blue, green, and red results. 



FIG. 57. CHOLESTEROL. 



(e) Schiff 's Reaction. To a little cholesterol in an evaporating dish add a few 

 drops of a reagent made by adding i volume of 10 per cent ferric chloride to 3 vol- 

 umes of concentrated sulphuric acid. Evaporate to dryness over a low flame and 

 observe the reddish-violet residue which changes to a bluish-violet. 



9. Preparation of Taurine. To 300 c.c. of bile in a casserole add 100 c.c. of 

 hydrochloric acid and heat until a sticky mass (dyslysin) is formed. This point 

 may be determined by drawing out a thread-like portion of the mass by means of a 

 glass rod, and if it solidifies immediately and assumes a brittle character we may 

 conclude that all the taurocholic and glycoholic acid has been decomposed. Decant 

 the solution and concentrate it to a small volume on the water-bath. Filter the 

 hot solution to remove sodium chloride and other substances which may have sepa- 

 rated, and evaporate the filtrate to dryness. Dissolve the residue in 5 per cent 

 hydrochloric acid and precipitate with 10 volumes of 95 per cent alcohol. Filter 

 off the taurine and recrystallize it from hot water. (Save the alcoholic nitrate for 

 the preparation of glycocoll, p. 211.) Make the following tests upon the taurine 

 crystals. 



