in the Structure of Calculi. 22 g 
To injure these calculi as little as possible, they were care- 
fully cut through with a fine saw, and a portion of the whole 
cut surface removed by a file ; in this way all the different 
ingredients of the calculi were obtained. 
In the experiments upon uric calculi from the bladder, I 
found, in most instances, a far more considerable loss in at- 
tempting to obtain their pure uric acid, than in the kidney 
calculi, which led me to suppose that they contained urea 
and that the presence of this substance, with some of the 
salts of urine, and with small portions of the ammoniaco- 
magnesian phosphate, was the cause of the occasional evolu- 
tion of ammonia when treated with the fixed alcalies, and of 
their easy solubility in those substances. 
To determine this point a small calculus, weighing twenty- 
five grains, and of the species commonly supposed to consist 
of urate of ammonia,* was digested for two hours with water 
in a very moderate heat. The water which had assumed a 
pale yellow colour was filtered off, and fresh water added to 
the residuum three successive times, when it appeared that 
every thing soluble in that fluid was separated. The insoluble 
part of the calculus being now carefully dried and weighed, 
was found to have lost 5.5 grains. 
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 phos- 
phate. 
• Fourcroy observes that urate of ammonia is easily detected by its rapid solu- 
bility in the fixed alcalies, and the odour of ammonia, which is perceived during its 
solution. — Vide Thomson’s Syst. of Chem. vol. v. p. 691. 
