402 



PHYSIOLOGICAL CHEMISTRY 



the solution to cool slowly and stand for some hours. This product should be per- 

 fectly pure creatine. If necessary it can be recrystallized with very little loss. The 

 crystallized product should be filtered off, washed with alcohol and ether and dried 

 in air for about half an hour. Thus obtained the creatine contains water of crystal- 

 lization which it loses very readily upon exposure to air. To prepare creatine which 

 can be weighed with absolute exactness it is necessary to dehydrate this product by 

 heating for some hours at about 95. 



The yield in this process is about 18 grams of recrystallized creatine, and 

 about 55 grams of creatinine zinc chloride recovered. Longer boiling with lime 

 does not bring about a greater yield, as after the 20-minute point creatine is de- 

 composed almost exactly as fast as it is formed. 



Examine the crystals of creatine under the microscope and compare with illus- 

 tration in Chapter XX on Muscular Tissue. For other creatine tests see Chapter 

 XX. 



FIG. 129. CREATININE-ZINC CHLORIDE. (Salkowski.) 



3. Nitro-prusside Test (Weyl). 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 452. 



4. Nitro-prusside-acetic Acid Test (Salkowski). To the yellow solution ob- 

 tained 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 precipitate of Prussian 

 blue may form. 



5. Picric Acid Reaction (Jaffe). 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. Glucose 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 526). 



ETHEREAL SULPHATES 



The most important of the ethereal sulphates found in the 

 urine are phenol-sulphuric acid, p-cresol-sulphuric acid, indoxyl-sulphuric 



