32 Observations on the Changes which take place 
watch-glass, there is often seen in the centre a kind of spume 
formed of a brown or yellow colour. This is more conspicuous 
if the experiment be performed on a larger scale. In such a case, 
having projected the nitrous on the uric acid, without diluting 
it, until the rapid decomposition has ceased, after some repose, 
a copious deposit of minute grains is formed *, On evaporat- 
ing the whole with a moderate heat, many suffocating white va- 
pours are disengaged, which become still more numerous in the 
rocess. After a time, the whole mass acquires a yellowish co- 
lotr and becomes fluid, but coagulates immediately if removed 
from the fire. Continuing therefore the heat, the vapours finally 
cease to be suffocating, and the mass acquires a brown colour, 
while the edges usually become of a rose colour. Urging the 
fire still further, white vapours continue to be disengaged ; mean 
time the mass becomes a bulky charcoal, which with a crack is 
in an instant almost entirely destroved. 
But, stopping here to consider the brown matter above men- 
tioned, it is at first so hard that with difficulty can it be re- 
moved from the vessel, although in a little time it attracts hu- 
midity and softens. Placed in water it dissolves, and communi- 
cates a citrine yellow colour, leaving behind a blackish matter. 
The solution has a slight acid taste, and reddens the blue tinc- 
ture of vegetables. Caustic potash either immediately or after 
a slight concentration produces a flaky precipitate, and at the 
same time ammonia is sensibly disengaged. Subcarbonate of 
potash produces a similar precipitate, which has a colour inclined 
to red. Treated with lime-water, the solution requires to be more 
concentrated to produce the precipitate, which assumes the form 
of very light flakes, which, on being reduced to dryness, become 
yellow shining scales. Similar scales are obtained even by evapo- 
rating the original simple solution. These salts have a sweetish 
taste, and are much more soluble in warm than cold fluids; they 
are deliquescent; but it appears that this property is greatly aug- 
mented by a particular yellowish matter which accompanies them, 
and which greedily attracts the humidity ofthe air, deliquescing 
itself, dissolving them with it, and even rendering them more 
soluble in water. 
The above solution decomposes immediately when brought 
into contact with a solution of lead or silver, and becomes turbid. 
If it be mixed with acetate of lead, the precipitate collected, and 
afterwards very well washed, and dried with a moderate heat, the 
salt of lead may then be decomposed by dilute sulphuric acid. 
* Bergman, operating directly on the calculi of uric acid, observed the 
constant formation of this deposit. It is indeed immaterial to this experi- 
ment, whether pure uric acid is used, or that which is found well farmed in 
human calculi. 
In 
