2 7 8 



PHYSIOLOGICAL CHEMISTRY, 



ditions. Collect the crystals on a filter paper and wash them with 

 alcohol to remove chlorides. Now treat the zinc chloride compound 

 with a little warm water, boil with lead oxide and filter. The fil- 

 trate may now be decolorized by animal charcoal, evaporated to 



FIG. 91. 



CREATININE-ZINC CHLORIDE. (Salkotvski.) 



dryness and the residue extracted with strong alcohol. (Creatine 

 remains undissolved under these conditions. ) The alcoholic extract 

 of creatinine is now evaporated to incipient crystallization and left 

 in a cool place until crystallization is complete. If desired the crys- 

 tals may be purified by recrystallization from water. 



2. Weyl's Test. Take 5 c.c. of urine in a test-tube, add a few 

 drops of sodium nitro-prusside and render the solution alkaline 

 with potassium hydroxide solution. A ruby-red color results which 

 soon turns yellow. See Legal's test for acetone, page 329. 



3. Salkowski's Test. To the yellow solution obtained in Weyl's 

 test above add an excess of acetic acid and apply heat. A green 

 color results and is in turn displaced by a blue color. A precipi- 

 tate of Prussian blue may form. 



4. Jaffe's Reaction. Place 5 c.c. of urine in a test-tube, add an 

 aqueous solution of picric acid and render the mixture alkaline with 

 potassium hydroxide solution. A red color is produced which turns 

 yellow if the solution be acidified. Dextrose gives a similar red 

 color but only upon the application of heat. This color reaction 

 observed when creatinine in alkaline solution is treated with picric 

 acid is the basic principle of Folin's colorimetric method for the 

 quantitative determination of creatinine (see page 392). 



