EXAMINATION OF URINARY DEPOSITS. 171 



The amount passed by an individual during each twenty-four 

 hours, varies from twenty to fifty ounces, holding in solution 

 from six hundred to seven hundred grains of solid matter. 

 When kept for some time it gradually becomes turbid, and de- 

 posits a sediment of earthly phosphates, previously held in 

 solution by the slight excess of acid present. If kept still 

 longer, it gradually putrefies, and, becoming concentrated by 

 evaporation, deposits small crystals of chloride of sodium, 

 phosphates, and other salts, and eventually becomes covered 

 with a grayish-colored mould. 



Urea appears to be the vehicle by which nearly the whole of 

 the nitrogen of the exhausted tissues of the body is removed 

 from the system. The proportion of urea in healthy urine 

 averages fourteen or fifteen parts in the one thousand. Pure 

 urea may be obtained by first converting it into the oxalate, 

 which is done by adding a strong solution of oxalic acid in hot 

 water, to urine previously concentrated to about one-eighth its 

 bulk, and filtered to free it from the insoluble sediments of 

 phosphates and urates. The crystal of oxalate of urea thus 

 obtained, a, Fig. 51, should be dissolved in hot water, and the 

 solution treated with pulverized chalk as long as effervescence 

 is produced. The urea remains in solution, and may be puri- 

 fied by boiling with animal charcoal, after which it may be 

 crystallized, in four- sided prisms, by careful evaporation. 



Nitrate of urea may be obtained in crystals, b, Fig. 51, by 

 concentrating urine to about one-half its bulk, and adding an 

 equal quantity of nitric acid. If urea be suspected in excess, 

 a drop of the urine, without concentration, may be treated with 

 nitric acid under the microscope. 



The proportion of uric acid in the healthy secretion varies 

 from 0-3 to 1-0 in 1000 parts. Its forms will be represented 

 when we treat of the examination of urinary deposits. It may 

 be obtained from urine concentrated to half its bulk, by adding 



