54 On Cystic Oxide, 
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 [ am under the necessity of acknowledging a mistake 
in the analysis of the mulberry calculus, though not of 
much importance. 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 cal- 
culus then under examinatton. 
In the analysis of the triple phosphate of magnesia, there 
is another mistake of more consequence. In my selection 
from numerous experiments for ascertaining the presence 
of phosphoric acid, I gave the preference to one in which 
nitrate of mercury was employed, on account of the facility 
of extracting the acid from the phosphate of mercury, by 
heat alone. But since the whole of the phosphoric acid is 
not precipitated by nitrate of mercury, sulphate of magnesia 
will not be formed on the addition of sulphuric acid, and 
the magnesia cannot be obtained separate by the same pro- 
cess. 
It may have been in consequence of this oversight, that 
a mistake on that subject has occurred in the succeeding 
volume of the Transactions. 
A calculus is there described, which had been taken by 
Mr. Thomas from the bladder ofa dog, and a series of ex- 
periments are related, from which it was inferred to consist 
of super-phosphate of lime, and phosphate of ammonia. 
But from the appearance of this calculus (which was ex- 
hibited to the Society at the time when the paper was read) 
I was much inclined to think that the nature of it was 
mistaken, and upon full consideration of the experiments, 
they did rot appear to me conclusive. 
I therefore obtained a portion of the calgulus, and by the 
following process, the earth contained in it was proved to 
consist almost wholly of magnesia, ' 
t 
