a new species of Urinary Calculus. 227 
a different shape, being nearly cubic. And it is possible, that 
the hexagonal crystals may owe their figure to a small por- 
tion 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 forma- 
tion of carbonic acid in distillation. The quantity of oxygen 
present in the calculus is not, however, sufficient to give it 
acid properties, for it has no effect on paper coloured with 
litmus. 
I am therefore inclined to consider it as an oxide ; and 
since both the calculi that have yet been observed have been 
taken from the bladder, it may be convenient to give it the 
name of cystic oxide, which will serve to distinguish it from 
other calculi ; and as this is unlike any other term at present 
employed in chemistry, it is to be hoped that it will not be 
thought to require any alteration. 
Since the period of my first essay on gouty and urinary 
concretions, the general results contained in it have been 
confirmed by others, and I believe are incontrovertible. But 
I am under the necessity of acknowledging a mistake in the 
analysis of the mulberry calculus, though not of much im- 
portance. An acid is mentioned to have arisen by sublimation, 
and it was supposed to originate from a partial decomposition 
of the oxalic acid. But since pure oxalate of lime yields no 
such sublimate, it most probably arose from the mixture of a 
small quantity of uric acid in the calculus' then under exami- 
nation. 
In the analysis of the triple phosphate of magnesia, there 
is another mistake of more consequence. In my selection 
