EXAMINATION OF NORMAL AND ABNORMAL URINE. 385 



acid), in order to allow the albumin to subside, when it can be 

 more distinctly seen and its quantity noticed. 



b. Nitric acid test. A test-tube is filled to the depth of about 

 half an inch with colorless nitric acid, and an equal quantity of 

 urine is allowed to flow down the side of the test-tube in such a 

 manner that the specifically lighter urine forms a distinct and 

 separate layer over the nitric acid. (If the urine be allowed 

 to flow from a pipette, the formation of the two strata is easily 

 accomplished.) In case albumin is present, a white band or 

 zone of varying thickness (according to the quantity of albumin 

 present) appears at the point of contact. 



If the urine be highly concentrated, a similar white zone is 

 formed between the acid and urine, due to the separation of in- 

 soluble acid urates; the difference between the separated urates 

 and albumin is that the latter forms a sharply defined zone, 

 whilst the urates diffuse into the urine above. Moreover, the 

 urates dissolve on the application of heat. Finally, the separa- 

 tion of acid urates may be avoided by diluting the urine with 

 an equal volume of water and placing this diluted urine upon 

 the nitric acid. 



c. Picric acid test. This test has the advantage that neither 

 phosphates nor urates can be mistaken for albumin. It consists 

 in slowly dropping urine into a test-tube filled to about one- 

 fourth with a highly colored solution of picric acid in water. 

 In the presence of albumin a white cloud or sharply defined 

 white turbidity is formed, and on warming the liquid the albu- 

 min collects into balls which rise to the surface of the liquid. 



In the above methods the manipulations and precautions are 

 so minutely described, in order to detect small quantities or even 

 traces of albumin. When albumin is abundantly present, there 

 is no difficulty whatever in its determination, as heat will pre- 

 cipitate it from an acid, neutral, or sometimes even alkaline 

 urine ; the precipitate should, however, always be tested by the 

 addition of a few drops of nitric acid, and the previous addition 

 of a few drops of acetic acid is also advisable. 



A neutral urine should never be acidified by nitric acid 

 (instead of acetic acid), because a drop or two of nitric acid 

 may in some cases prevent the coagulation of albumin by 

 heat, though a larger quantity (10 to 20 drops) has no such 

 effect. 



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