r.-* 
UR A 
• Tlie third ore of the metal is the native 
carbonate of nranium. Of tliis tliere are 
two distinct varieties, tlie one of a pale 
preen, and sometimes of a silvery white 
colour. This contains but a small quantity 
of the oxide of copper, and is very rare. 
Tlie other is of a shining deep green, which 
is the green mica, or glimmer, of mineralo- 
gists. Klaproth supposed that it contained 
an oxide of nranium, mixed with the oxide 
of copper ; but it has been since discovered 
to have carbonic acid in its composition. 
It is crystallized in small square plates, and 
sometimes, though rarely, in complete oc- 
tahedrons. 
The process by which Klaproth reduced 
this metal is the following : He mixed the 
yellow oxide of uranium, precipitated from 
its solutions by an alkali, with linseed oil, in 
the form of a paste, and this being exposed 
to a strong heat, there remained a black 
powder, which had lost rather more than 
one-fourth of its weight. It was then ex- 
posed to the heat of a porcelain furnace, in 
a close crucible, and the oxide was after- 
wards found in a coherent mass, but friable 
under the lingers, and reduced to a black 
shining powder. It decomposed nitric acid 
with effervescence. This black powder, 
covered with calcined borax, was for the 
second time exposed to a still stronger 
heat, by which a metallic mass was obtain- 
ed, consisting of very small globules adher- 
ing together. 
The colour of uranium iS of a dark grey , 
and internally of a pale brown. It has little 
brilliancy, on account of the spongy mass 
in which state it is obtained. It may be 
scratched with a knife, and is extremely in- 
fusible. The specific gravity is 6.4. When 
uranium is exposed to a red heat in the 
open air, or w'hen it is acted on by the 
blow-pipe, it undergoes no change. The 
yellow oxide of uranium does not melt. It 
acquires a brownish-grey colour when it is 
long heated in the air, but it has not been 
ascertained whether it gains or loses oxygen. 
The oxide of uranium is reduced by means 
of charcoal, when it is exposed to heat. 
The yellow oxide, when mixed with com- 
mon enamelling flux, tinges porcelain of a 
deep orange colour. 
URANIA, in botany, a genus of the 
flexandria Monogynia class and order. 
Natural order of Musae, Jussieu. Essential 
character; calyx none ; corolla three-petal- 
ed ; nectary two-leaved, with one of the 
leaves bifid ; capsule inferior, three-celled, 
many-seeded j seeds in two rows, covered 
URE 
with an aril. There is only one species, 
riz. U. speciosa, a lofty tree, growing 
naturally in the marshy places of Mada- 
gascar. 
URANOSCOPUS, the star-gazer, in na- 
tural history, a genus of fishes of the order 
Jugulares. Generic character : head large, 
depressed, rough ; mouth with an internal 
cirrus ; gill-membrane with six papillous- 
toothed rays ; gill-covers edged with a mem- 
branaceous fringe. 
U. scaber, or the bearded star-gazer, is a 
native of the Mediterranean, and frequents 
deep places near the shores, feeding on 
aquatic insects and small fishes, which it 
decoys within its reach by waving the long 
cirrus of the mouth in various directions. 
The smaller fishes mistake these for worms, 
and in endeavouring to seize the supposed 
food are themselves caught and devoured 
by the star-gazer, which lay imbedded and 
unobserved in the mud or gravel of the 
bottom. ^ 
URENA, in botany, a genus of the Mo- 
nadelphia Polyandria class and order. Na- 
tural order of Coliimuiferae. Malvaceae, 
Jussieu. Essential character: calyx double, 
outer five-cleft; capsule five-cleft, divisible 
into five parts, with the cells closed, and 
one seed in each. There are eight species. 
URETHRA. See Anatomy. 
UREA, in chemistry. The nature and 
properties of urea have been chiefly inves- 
tigated by Fourcroy and Vauquelin. It is 
obtained from urine. It may be extracted 
by the following process: If a quantity of 
human urine which has been passed a few 
hours after taking food, be evaporated with 
a gentle heat, to the consistence of a thick 
syrup, and allowed to cool, it concretes into 
a crystalline mass. Add to this mass, in se- 
parate portions, four times its weight of 
alcohol ; with the application of a gentle 
heat, great part is dissolved, and w hat re- 
mains consists of different saline substances. 
Separate the solution from the undissolved 
part, and introduce it into a retort. Distil 
with the heat of a sand-bath, and continue 
the boiling till the liquid is reduced to the 
form of a thick syrup. The matter which 
remains in the retort crystallizes as it cools. 
The crystals thus formed are urea. 
Urea, which is prepared by this process, 
is crystallized in the form of plates, crossing 
each other. It is viscid, resembling thick 
honey, and of a yellowdsh-white colour. It 
has a strong acrid taste, anda fetid alliaceous 
smell. It deliquesces in the air, and by 
attracting moisture is converted into a thick 
