URINARY CALCULI. 451 



Brugnatelli states that he examined an urinary secretion con- 

 sisting of carbonate and oxalate of lime, and benzoate of 

 ammonia. 



When carbonate and oxalate of lime occur together, the cal- 

 culus dissolves in hydrochloric acid with effervescence, both be- 

 fore and after heating. Before the application of heat it is par- 

 tially soluble in acetic acid with effervescence, the oxalate 

 remaining undissolved. 



On dissolving a portion of the calculus in dilute hydrochloric 

 acid, and adding ammonia, we precipitate the oxalate of lime ; 

 the lime corresponding to the carbonate may then be precipi- 

 tated from the filtered solution by oxalate of ammonia. The 

 oxalate of lime precipitated by ammonia may be easily mistaken 

 for phosphate of lime ; all ambiguity may, however, be avoided 

 by recollecting that the oxalate may be converted by heat into 

 carbonate of lime, which dissolves with effervescence in acids 

 from which it is not precipitable by ammonia, while the phos- 

 phate of lime is unaffected by heat, and dissolves without effer- 

 vescence in hydrochloric acid from which it may be thrown 

 down by ammonia. When carbonate of lime is associated 

 with oxalate and phosphate of lime, the calculus dissolves 

 with effervescence in hydrochloric acid both before and after 

 heating. In this case the oxalate of lime may be readily over- 

 looked, but on dissolving a fragment of the calculus in hydro- 

 chloric acid, and precipitating with ammonia, the oxalate and 

 phosphate of lime are thrown down together, while the carbonate 

 of lime exists in the filtered solution as chloride of calcium, and 

 may be precipitated by oxalate of ammonia. On drying and 

 gently heating the mixture of oxalate and phosphate of lime, 

 the oxalate becomes converted into carbonate. We then dis- 

 solve the heated residue in hydrochloric acid, precipitate the 

 phosphate of lime with ammonia, filter, and throw down the 

 lime from the filtered solution with oxalate of ammonia. This 

 lime corresponds with the original oxalate. When the car- 

 bonate is mixed with urate of lime, the latter must be taken 

 up with boiling water. 



Carbonate of magnesia is only rarely associated with car- 

 bonate of lime in urinary calculi, although Berzelius supposes 

 that they always occur together. In order to separate them, 

 they must be dissolved in hydrochloric acid, and the cliloride 

 of magnesium then taken up by alcohol. 



