a new Species of Urinary Calculus. 53 
It is also dissolved readily by pure alkaline menstrua: by 
potash, by soda, by ammonia, and by lime-water. It is 
even dissolved by fully saturated carbonates of potash or of 
soda. Accordingly, these alkalies are not so convenient for 
the precipitation of this matter from acid solutions, as the 
carbonate of ammonia, which is not capable of redissulying 
the precipitate, though added in excess. 
For a similar reason, the acids best suited for its precipi- 
tation from alkaline solutions, are the acetic and citric acids. 
But the tartaric acid may occasion an appearance of precipi- 
tation, by forming a supertartrate with the alkali employed. 
The combination of this substance with acids, may be 
made to crystallize without difficulty, and they form slender 
spicula radiating from a centre, which readily dissolve again 
in water, unless they have been injured by being in any 
degree over-heaied. 
The niariatic sait is decomposed by the heat of boiling 
water, en account of the volatility of the acid, and the rest 
are easily destroyed by a greater excess of heat. 
The salt formed by combination with nitric acid, does 
not yield oxalic acid, and does not become red, as the uric 
acid does, when similarly treated; but it turns brown, be- 
coming gradually darker, till it is ultimately black. 
When the combinations with alkalies are evaporated, they 
leave small granular crystals ; but as I was desirous of ren- 
dering my experiments as numerous as a limited quantity 
would permit, the portion which I could employ in any 
one experiment was too small for me to attempt to deter- 
mine the form of such crystals. 
When a hot solution in potash was neutralized by distil- 
led vinegar, the precipitate did not immediately take place, 
but formed gradually during the cooling of the liquor in 
minute crystals, some at the surface of the fluid, and others 
attached to the sides of the vessel, The only definite form 
which I could observe, was that of flat hexagonal plates, 
but I could discern nothing which enabled me to, judge of 
the primitive form of the crystal. On the surface of the 
calculus belonging to Guy’s hospital, some minute crystals 
may be discerned, of a different shape, being nearly cubic, 
And it is possible, that the hexagonal crystals may owe their 
figure to a small portion of alkali remaining in combination. 
From the ready disposition of this substance to unite with 
both acids and alkalies, it would appear to be an oxide; and 
that it does, in fact, contain oxygen, is proved by the for- 
mation of carbonic acid in distillation. The quantity of 
oxygen present in the calculus is not, however, sufficient to 
D3 give 
