URINE. 175 



clears throughout its whole extent: on being allowed to cool it 

 again becomes turbid, and deposits the sediment afresh. If a 

 portion of the sediment, after being washed, is rubbed with 

 caustic lime, a perceptible odour of ammonia is developed : and 

 if a few drops of nitric acid are poured over it in a porcelain 

 basin, and gentle heat applied, the purple colour, indicating the 

 presence of uric acid, appears. On heating a little of it on 

 platinum foil, it burns away without a residue. 



2. If uric acid is mixed with the urate of ammonia, the sedi- 

 ment sinks rapidly to the bottom, as a dense granular powder, 

 after the fluid has been cleared by the application of heat. If 

 hydrochloric acid is added, after the urate of ammonia has been 

 dissolved by heat, the precipitate on cooling consists of uric acid 

 alone. 



3. If earthy phosphates are mixed with the urate of am- 

 monia, the urine is either neutral or alkaline, and is only 

 partially cleared by heat. The turbidity which remains, pro- 

 duced by the earthy phosphates in suspension, disappears imme- 

 diately upon the addition of hydrochloric acid. Free uric acid 

 is precipitated on cooling. 



4. If mucus or pus is mixed with the urate of ammonia the 

 fluid becomes only partially cleared on warming, neither does it 

 become perfectly clear on the addition of hydrochloric acid, since 

 mucus and pus are not dissolved by that agent. If there should 

 be so large a proportion of mucus and earthy phosphates mixed 

 with the urate of ammonia, that the solution of the latter salt 

 on the application of heat produces no perceptible effect, it 

 will only be necessary to filter the heated urine, and to allow it 

 to cool. The separation of urate of ammonia on cooling renders 

 it turbid, and crystals of uric acid may be obtained on the 

 addition of hydrochloric acid. 



5. If urine containing urate of ammonia is albuminous, it is 

 necessary to be very cautious in the application of heat as a test. 

 On gently warming the tube, the urate of ammonia dissolves 

 before the albumen begins to coagulate. If the fluid which 

 has thus become clear is exposed to a stronger heat, it becomes 

 cloudy, the turbidity commencing in the upper, hottest stratum 

 of fluid, and gradually extending itself. 



Urate of ammonia is recognized under the microscope as an 



