URINE 347 



Do not add acetic acid before heating: (1) because albumin, 

 if present, may be converted into acid albumin; (2) because 

 acid tends to disintegrate cellular elements which may be 

 present, with the consequent separation of cell-proteins. The use 

 of strong mineral acids in this test is objectionable for simi- 

 lar reasons. 



46. Heller's Nitric Acid Test. To four c.c. of urine in a test 

 tube add, by means of a pipette, a few cubic centimeters of 

 concentrated nitric acid. Run in carefully, so that two distinct 

 layers may be formed. In the presence of albumin or globu- 

 lin, a distinct white ring will form at the junction of the 

 two layers. 



The following important facts should be taken into con- 

 sideration: Not over five minutes should be occupied in this 

 test, since prolonged action of nitric acid will separate cell- 

 proteins, which may be present. 



When urea is present in large quantities, particularly if 

 the volume of the urine is low, crystals of urea nitrate may 

 be deposited at the line of contact of the two liquids. The 

 crystalline character of this material suffices for differentiation. 



In the presence of large quantities of uric acid, a whitish 

 ring may appear several mm. above the line of contact. If 

 doubt exists as to either of these two conditions, dilute the urine 

 and repeat the test. If the ring was due to uric acid or urea, it 

 will fail to appear after dilution. A cloud, high up in the urine, 

 may be caused by mucin. The pigments form rings of dark 

 color between the urine and the acid. These rings, once recog- 

 nized, cannot be mistaken for proteins. A ring due to certain 

 ingested substances, e. g., copaiba, may be dissolved with ether; 

 iodine, excreted in the urine, forms a dark ring at the surface 

 of the nitric acid. Indican is the most common pigment produc- 

 tive of colored rings. 



47. F errocyanide Test. Add a few drops of potassium ferro- 

 cyanide solution to the clear urine and then acidify with acetic 

 acid. In the presence of albumin or globulin, a white cloud or 



