. of Urinary Concretions. 41 
Her prefcription brought into vogue the theory of thefe me- 
dicines operating by their caufticity. The fuccefsful ufe, by 
Mr. Colborne, of potafh faturated with carbonic acid, ac- 
cording to the difcovery of Bewley and Bergman, and the 
fill further improvement in praétice, from the ufe of foda, 
as well as potafh, fuper-faturated with carbonic acid, by the 
difcovery of a peculiar method by Mr. Schweppe, have 
completely refuted the theory of the agency of alkalies on 
the principle of caufticity. 
It appears, from the preceding brief hiftory, as jwell as 
from the confeflion of the lateft and beft writers, that the 
experiments hitherto made, rather “ afiord indications of 
what remains to be done, than furnifh demonftrations of the 
nature of anintal concretions.” It is alfo too obvious to 
need explanation, that more efficacious and innocent prac- 
fice, in difeafes from thefe concretions, can only be dif- 
covered by a further inveftigation of their properties. It is 
with this view, as well as for the fake of chemical philofo- 
phy, that I think it.my duty to fubmit to the Society fome 
of the obfervations I have made, in the courfe of inquiry on 
this fubject. 
The obfervations which I fhall now offer, are principally 
on a fubftance, which my experiments inform me is very 
generally a conftituent of both urinary and arthritic concre- 
tions. It is a fubftance obtained by diffolving it out of theie 
concretions, by lye of cauftic fixed alkali, and precipitating 
it from the folution by acids. In this way, Scheele feparated 
this matter; but he did not confider its importance, nor of 
courfe at all inveftigate its properties. He does not even 
feem to have been aware that it was a diftin& conftituent 
part of the urinary concretion ; for, when he relates the ex- 
periment of precipitating matter from the nitric folution of 
calculus by metallic falts, no diftinétion is made between 
the precipitations in this experiment, and that in the former: 
yet we can now fhow, that in the one cafe the precipitate 
js a peculiar animal oxide, and in the other they are metallic 
pholphates, 
