— 
a new Species of Urinary Calculus. 55 
Tt was dissolved, with the exception of a very small resi- 
duum, by distilled vinegar. 
_. The whole of the phosphoric acid was then precipitated 
by acetate of Jead, added to excess. 
The liquor was then poured off, and sulphuric acid was 
added, which precipitated the excess of lead, and at the same 
time formed sulphate of maguesia in solution. 
By evaporation to dryness, the acetic acid was removed, 
and by subsequent increase of heat, the suiphate of ammo- 
nia and excess of sulphuric acid were expelled. 
The residuum being then dissolved in water, and the liquor 
suffered to crystallize by spontaneous evaporation, there re- 
mained a quantity of sulphate of magnesia, that weighed 
rather more than the quantity of calculus taken for the ex- 
periment. 
It was evident, therefore, that in this instance, the cal- 
culus examiued did not consist of super-phosphate of lime, 
and there is some reason to doubt, whether a compound, 
that is so very solutle in water, ever forms a part of urinary 
concretions. 
Although the treatment of diseases is not in general a 
fit subject to occupy the time of this Society, there is never- 
theless one suggestion, with respect to the prevention of 
calculous complaints, so nearly connected with my present 
subject, that I think it may deserve to be recorded. 
Since the white matter contained in the urine of birds, 
which is voided along with their dung, has been remarked 
by M. Vauquelin to consist principally of uric acid, I have 
paid some attention to the different proportion in which 
this matter is voided by different species of birds, to see 
how far it accorded with the different qualities of their food. 
And I found that in the dung of the goose, feeding wholly 
on grass, the proportion did not seem so much as 51. of 
the whole dung. In that of a pheasant kept in a cage, and 
fed on barley alone, it was about +4; part. In that of a hen, 
having the range of a garden and farm-yard, and conse- 
quently procuring insects, and possibly other animal food, 
the proportion was manifestly much greater, and combined 
with lime. In the dung of a hawk, fed upon flesh alone, 
the quantity of. matter voided in a solid state bears but a 
small proportion to the residuum of uric acid that is left 
by the urine when dry. And in the gannet, feeding solely 
on fish, 1 have observed the evacuations in some instances 
to be mere urine, for it contained no solid matter, except- 
ing the uric acid. 
Jt seems consequenily deserving of inquiry, what changes 
might 
