392 PHYSIOLOGICAL CHEMISTRY. 



urates, calcium oxalate, phosphate, or carbonate, magnesium- 

 ammonium phosphate, cystin, hippuric acid, etc. 



The chemical examination of any urinary sediment^ should 

 always be preceded by a microscopical examination, which latter 

 is in many cases the only way of determining the nature of the 

 sediment, especially of the organized substances. Most of the 

 unorganized and either crystalline or amorphous sediments may 

 be easily recognized by chemical means. 



Urates of ammonium, calcium, and sodium dissolve on heating 

 the urine, arid are reprecipitated on cooling. The murexid test 

 is used in addition. 



Phosphates of calcium or ammonium-magnesium dissolve in acetic 

 acid, and ammonium molybdate dissolved in nitric acid produces 

 a yellow precipitate on heating. 



Calcium oxalate is insoluble in acetic, but soluble in hydro- 

 chloric acid, from which solution it is reprecipitated on neutraliz- 

 ing with ammonia. 



Uric acid is not dissolved by heat, nor by acetic or hydro- 

 chloric acid, but burns on platinum foil without leaving a 

 residue; it is recognized by the murexid test. 



Urinary calculi are solid deposits of larger or smaller size- 

 formed from the urine within the tracts (kidneys, ureter, 

 bladder, and urethra). The chemical composition of the calculi 

 is generally that of either of the above-named unorganized 

 sediments, and their nature can easily be determined by using 

 the tests mentioned for them. 



Most common are calculi of uric acid; often met with are 

 those of urates, phosphates, and oxalates; rarely, however, those 

 of xanthin and cystin. 



QUESTIONS. 



531. What points are to be considered, and what substances deter- 

 mined in the analysis of normal and abnormal urine? 



532. What is the color of urine, and what are the chief causes influ- 

 encing the color? 



533. What is the specific gravity of healthy urine, how is it deter- 

 mined, and how is the total amount of solids approximately calculated 

 from the specific gravity? 



