- ^ URI 
brown liquid It is very soluble in water, 
and also in alcohol. The solution in water 
concentrated, is of a brown colour. This 
solution is gradually decomposed, air is 
emitted, which is partly composed of am- 
monia, and acetic acid is formed in the 
liquid. If the solution in water be boiled, 
and as the evaporation goes on fresh por- 
tions of water be added, the urea is decom- 
posed ; carbonate of ammonia is disengag- 
ed, while acetic acid is formed, and char- 
coal precipitated. Tlie component parts 
of urea, therefore, are supposed to be 
Oxygen 39.5 
Azote 32.5 
Carbon 14.7 
Hydrogen 13.3 
100.0 
The caustic fixed alkalies readily dissolve 
urea, and disengage from it ammonia ; and 
the solution contains tlie benzoic, acetous, 
and carbonic acids, united with the alkali 
employed. The urea almost entirely dis- 
appears from urine during certain diseases, 
and a very large quantity of saccharine mat- 
ter is produced, which when evaporated 
and clarified resembles Muscovado sugar. 
URIC acid. This acid was discovered 
by Scheele in the year 1776. It was at first 
called litliic acid. It constitutes one of the 
component parts of urinary calculi, and is 
also found in human urine. There is one 
species of calculus which is almost entirely 
composed of this substance; it is that 
sjiecies which resembles wood in appear- 
ance and colour. Thik acid is insipid, in- 
odorous, almost insoluble in cold water, and 
soluble only in about 360 parts of boiling 
water. It separates fi om this when it cools, 
into small yellowish crystals. The solution 
in water reddens the tincture of turnsole. 
There is scarcely any action between the 
tsric acid and the sulphuric and nturiatic 
acids. It is soluble in the concentrated 
nitric acid, to which it communicates a red 
colour. It would appear that in this change 
of colour the nature of the acid is also 
changed, for part of it is converted into 
oxalic acid. Oxyninriatic acid very readily 
acts upon uric acid, either by suspending a 
calculus in the liquid acid, or, which is 
easier, by passing a stream of oxymuriatic 
acid gas through water, at the bottom of 
which is placed the uric acid in powder. 
Its colour becomes pale, the surface swells 
up, it softens, and is at last converted into 
a jelly. This part disappears, and is soon 
dissolved, giving a milky colour to the 
URI 
liquid. There is extricated, by slow effer- 
vescence, small bubbles of carbonic acid 
gas. The liquid by evaporation gives mu- 
riate of ammonia, acidulous oxalate of am- 
monia, both crystallized ; muriatic acid, and 
malic acid. Thus the oxymuriatic acid de- 
composes the uric acid, and converts it into 
ammonia, carbonic, oxalic, and malic acids. 
Various facts show that uric acid is a com- 
pound of a very peculiar kind, formed of 
azote, of carbon, of hydrogen, and oxygen, 
and susceptible of a great number of diffe- 
rent changes by chemical agents. 
URINL. The properties of urine vary 
considerably, according to the consti- 
tution and health of the body, and the 
period when it is voided after taking food. 
The urine of a healthy person is of a light 
orange colour, and uniformly transparent. 
It has a slightly aromatic odour, in some de- 
gree resembling that of violets. It has a 
slightly acrid, saline, bitter taste. The spe- 
cific gravity varies from 1.005 to 1.033. 
The aromatic odour, which leaves it as it 
cools, is succeeded by what is called the 
urinous smell, which latter is converted to 
anotlier, and, finally, to an alkaline odour. 
Urine converts the tincture of turnsole into 
a green colour, from which it is concluded 
that it contains an acid. No less than thirty 
different substances have been detected in 
urine by chemical analysis ; viz. a great va- 
riety of salts, acids, ammonia, &c. 
Urine is much disposed to spontaneous 
decomposition. The time when this pro- 
cess commences, and the rapidity of the 
changes which take place, depend on the 
quanxity of the gelatine and albumen. When 
the proportion of these substances is con- 
siderable, the decomposition is very rapid. 
This is owing to the great number of sub- 
stances, and.the united force of their attrac- 
tions overcoming the existing affinities of 
the different compounds of which fresh 
urine consists, and especially to the facility 
with which urea is decomposed. This sub- 
stance is converted during putrefaction into 
ammonia, carbonic acid, and acetic acid. 
Hence the smell of ammonia is' always re- 
cognized while urine is undergoing "these 
changes. Part of the gelatine is deposited 
in a flaky form, mixed with mucilage. Am- 
monia combines with phosphoric acid, and 
the phosphate of lime is precipitated. It 
combines also with phosphate of magnesia, 
and forms a triple salt. The other acids, 
the uric, benzoic, the acetic, and carbonic 
acids, are all satmated with ammonia. See 
Physiology. 
