URINE AND ITS CONSTITUENTS. 725 



the zone of contact, the extent and intensity of the cloud varying 

 with the quantity of albumin present. Very small quantities of 

 albumin cannot be detected at once, but will appear on standing, the 

 cloudiness extending gradually upward. A distinct ring from 1 to 2 

 cm. above the zone of contact, and appearing within five to ten 

 minutes after the addition of nitric acid, was formerly thought to be 

 due to uric acid, and was called the urate ring. It is believed now 

 to be in some cases composed of protein material. In urines contain- 

 ing a high percentage of urea, a ring may form at the plane of con- 

 tact, consisting of urea nitrate, which is distinctly crystalline in 

 appearance. Following the ingestion of turpentine and various bal- 

 sams, this test may show a precipitate of resinous acids at the junc- 

 tion of urine and acid, which is recognized by its solubility in alcohol 

 or ether. Albumoses produce a ring which dissolves on heating and 

 reappears on cooling. 



At the zone of contact a change in color is generally noticed. In 

 normal urine this varies from pale red to intense brick red ; in biliary 

 urine a color- play similar to the colors of the rainbow may be noticed, 

 while the presence of indican is indicated by a violet or blue tint. 

 It is important to distinguish between color rings and precipitate 

 rings. 



3. Trichlor acetic acid may be used for the detection of albumin by 

 dropping a fragment into a few cubic centimeters of urine contained 

 in a test-tube. As the acid dissolves, a cloudy ring forms in the pres- 

 ence of albumin, which is not dissolved on warming. 



4. Potassium ferrocyanide test. 5 to lOc.c. of cold urine are acidu- 

 lated with 5 to 10 drops of acetic acid, and to the mixture are added 

 a few drops of solution of potassium ferrocyanide. In the presence 

 of even traces of albumin a turbidity is caused. A precipitate which 

 dissolves on heating is due to albumose. This test is extremely deli- 

 cate, especially when modified so as to allow a few cubic centimeters 

 of diluted acetic acid, to which a few drops of potassium ferrocynaide 

 solution had been added, to flow down the side of the test-tube con- 

 taining the urine. A decided turbidity at the point of contact of the 

 two liquids shows albumin. 



In case the addition of acetic acid to the cold urine should cause a 

 turbidity (which may be due to mucin or nucleo-albumin) it must be 

 filtered before adding the potassium ferrocyanide. 



In the above methods the manipulations and precautions are mi- 

 nutely described, in order to detect small quantities or even traces of 

 albumin. When albumin is abundantly present, there is no difficulty 



