132 LABORATORY WORK IN PHYSIOLOGICAL CdE.tliX 



enough iodo-potassium iodide to give the solution a decided 

 yellow color Warm at 65 C. for 5 minutes and allow to 

 cool. A yellow precipitate of iodoform settles out, recogniza- 

 ble by its odor and its hexagonal crystals. This test is also 

 given by alcohol. 



(6) Gunning's Modification. In this test ammonia is 

 substituted for the sodium carbonate and a tincture of iodine 

 in place of the iodopotassium iodide. A black precipitate of 

 iodide of nitrogen is first formed, but this gradually disappears 

 on standing, leaving the iodoform visible, if present. Alcohol 

 or aldehydes do not give this reaction. 



(c) LegaVs Test. To a few c.c. of the distillate add a few 

 drops of a freshly prepared solution of sodium nitroprusside 

 and make the solution alkaline with NaOH. A ruby-red 

 color is produced which quickly disappears. Creatinine also 

 gives this reaction. If the alkaline acetone solution is treated 

 with a large excess of acetic acid, the color becomes red, 

 whereas in the case of creatinine it is changed to green and 

 then blue. 



(d) Lange's Modification of LegaVs Test. To 15 c.c. of 

 urine add one c.c. of glacial acetic acid, and two or three drops 

 of a freshly prepared solution of sodium nitroprusside. Mix 

 this solution well and carefully stratify upon it concentrated 

 ammonium hydroxide. At the line of contact a violet ring 

 will appear. This reaction is not given with creatinine, 

 alcohols or aldehydes. 



EHRLICH'S DIAZO REACTION. 



Diazobenzenesulphonic acid comes into prominence as a 

 reagent in various connections. 



It is employed in the detection of sugar, protein, bilirubin, 

 and an unknown chromogen of the urine which is so com- 

 monly present associated with certain pathological conditions 

 (typhoid, pulmonary tuberculosis, etc.). It is especially 

 as a test for this unknown substance or substances that 



