224 
Mr. W. Brande on the Differences 
SECTION I. 
Of Calculi formed in the Kidnies, and voided without having 
afterwards undergone any Change in the urinary Passages. 
These have the following properties : 
They are of a brownish yellow colour, sometimes of a 
grayish hue, which seems to arise from a small portion of dry 
mucus adhering to their surface. 
They are entirely soluble in a solution of pure potash, and 
during their solution, they seldom emit an odour of ammonia. 
When heated to dryness, with nitric acid, the residuum is 
of a fine and permanent red colour. 
When exposed to the action of the blow-pipe, they blacken 
and emit a strong odour of burning animal matter, very dif- 
ferent from that of pure uric acid. This arises from a variable 
proportion of animal matter which they contain, and which 
occasions the loss in the analysis of these calculi. Its relative 
quantity is liable to much variation, as may be seen from the 
following statements. 
A calculus from the kidney, weighing seven grains, was 
dissolved in a solution of pure potash. A quantity of muriatic 
acid (rather more than sufficient for the saturation of the 
potash) was added, and the precipitate of uric acid thus ob- 
tained weighed when dry 4,5 grains. No other substance, 
except animal matter, which was evident on attempting to 
obtain the muriate of potash, could be detected, consequently 
the composition of this calculus was as follows : 
