172' On the Differences in the Structure of Calculi. 



The aqueous solution was evaporated by a gentle heat, 

 nearly to dryness, and a substance was' obtained having all 

 the properties of urea, in combination with a small portion 

 of muriate of ammonia, and of the ammoniaco-magnesian 

 phosphate. 



Sixty grains of another calculus of a considerable size, 

 supposed, from a superficial analysis, to consist of nearly 

 pure urate of ammonia, were digested at a low temperature 

 in one ounce of alcohol. In an hour the alcohol was de- 

 canted off, and fresh portions were added successively, a$ 

 long as it appeared to act upon the calculus, which, after 

 having been carefully dried in a temperature below 212°, 

 weighed 54*8 grains, so that 5*2 grains had been taken up 

 by the alcohol. 



On evaporating the alcoholic solutions, a substance was 

 obtained having all the properties of urea, with a small por- 

 tion of saline matter, probably muriate of ammonia, as by 

 the addition of potash a slight ammoniacal odour was per- 

 ceptible ; its quantity however was too minute for accurate 

 examination. 



The remaining portion of the calculus, weighing 54"8 

 grains, was treated with small portions of acetic acid, by 

 which six grains of the ammoniaco-magnesian phosphate 

 were obtained. 



The part of the calculus remaining after this treatment, 

 weighing 4S*8 grains, was perfectly soluble in a splution of 

 pure potash ; it emitted no ammoniacal odour when acted 

 upon by the alkali, and possessed the properties of pure uric 

 flcid._ 



The following therefore is the composition of this calculus. 



Grains. 



Urea, and muriate of ammonia 5*2 



Ammoniaco-magnesian phosphate f5- 

 Uric acid - - 48*8 



60- 



From these and many similar experiments upon other cal- 

 culi, hitherto generally supposed to consist of urate of am- 

 monia, I am induced to believe that the evolution of am- 

 monia 



