IRE 
a space for one day’s work, which may not 
be interesting, and can therefore be told in 
a few lines, as for another, which may pro- 
bably abound with important incidents, and 
consequently require much room. Accord- 
ing to circumstances the matter must be 
greater or less, and the appropriated space 
should admit of all.' 
JOURNEYMAN, properly one who 
works by the day only ; but it is now used 
for any one who works under a master, 
either by the day, the year, or the piece. 
JOY, one of the most powerful mental 
emotions accompanied with an extraordi- 
nary degree of animation and pleasure. 
The effect of joy, if not too violent, invigo- 
rates the whole animal frame. But sudden 
and excessive joy is often as injurious as 
the operation of either grief or terror, and 
there are a thousand instances on re- 
cord, in which the precipitate communica- 
tion of unexpected good news has proved 
fatal. 
IPECACUANHA. See Materia Me- 
dica. 
IPOMOEA, in botany, a genus of the 
Pentandria Monogynia class and order. 
Natural order of Campanacese. Convolvu- 
li, Jussieu. Essential character: corolla 
funnel-form ; stigma headed globose ; cap- 
sule three-celled. There are twenty-seven 
species, of which I. quamoclit, winged-leav- 
ed ipomoea is an annual plant, rising with 
oblong, broad seed leaves, which remain a 
considerable time before they fall off; stems 
slender, twining, rising by support to the 
height of eight feet, sending out several 
side branches, which twine about each 
other. The flowers come out singly from 
the side of the stalks, on slender peduncles 
an inch long. The tube of the corolla is 
about the same length, narrow at bottom, 
and gradually widening to the top, where 
it spreads open, flat, with five angles. It is 
of a beautiful scarlet colour, making a fine 
appearance. It is a native of both Indies. 
IRESINE, in botany, a genus of the 
Dioecia Pentandria class and order. Na- 
tural order of Holoraceae. Amaranthi, 
Jussieu. Essential character: calyx two- 
leaved ; corolla five-petalled : male, nec- 
tary seven : female, stigmas two, sessile ; 
capsule with tomentose seeds. There is 
only one species, viz. I. celosia, a perennial 
weak plant requiring support, rising twelve 
feet in height, having large knots at each 
joint, with oval lanceolate smooth leaves ; 
stems very diffused, branching out on every 
side ; flowers terminating in slender loose 
IRI 
panicles, covered with a silky down, of a 
pale yellow colour. Native of Jamaica 
and other Islands in the West Indies. 
IRIDIUM. Mr. Tennant, on examinirfg 
the black powder left after dissolving pla- 
tina, which from its appearance had been 
supposed to consist chiefly of plumbago, 
found it contained two distinct metals never 
before noticed, which he has named iridium 
and osmium. The former of these was 
observed soon after by Descostils, and by 
Vauquelin. 
To analyse the black powder, Mr.Tennant 
put it into a silver crucible with a large 
proportion of pure dry soda, and kept it in 
a red heat for some time. The alkali being 
then dissolved in water ; it had acquired a 
deep orange or brownish yellow colour, but 
much of the powder remained undissolved. 
This digested in muriatic acid gave a dark 
blue solution, which afterward became of a 
dusky olive green, and finally, by continu- 
ing the heat, of a deep red. The residuum 
being treated as before with alkali, and so 
on alternately, the whole appeared capable 
of solution. As some silex continued to be 
taken up by the alkali, till the whole of the 
metal was dissolved, it seems to have been 
chemically combined with it. The alkaline 
solution contains oxide of osmium, with a 
small proportion of iridium, which separates 
spontaneously in dark-coloured thin flakes 
by keeping it some weeks. 
The acid solution contains likewise both 
the metals, but chiefly iridium. t By slow 
evaporation it affords an imperfectly cry- 
stallized mass; which, being dried on blot- 
ting-paper, and dissolved in water, gives 
by evaporation distinct octaedral crystals. 
These crystals, dissolved in water, produce 
a deep red solution inclining to orange. 
Infusion of galls occasions no precipitate, 
but instantly renders the solution almost 
colourless. Muriate of tin, carbonate of 
soda, and prussiate of potash, produce near- 
ly the same effect. Ammonia precipitates 
the oxide, but, possibly from being in ex- 
cess, retains a part in solution, acquiring a 
purple colour. The fixed alkalies precipi- 
tate the greater part of the oxide, but re- 
tain a part in solution, this becoming yellow. 
All the metals that Mr.Tennant tried, ex- 
cept gold and platina, produced a dark or 
black precipitate from the muriatic solution, 
and left it colourless. 
The iridium may be obtained pure, by 
exposing the octaedral crystals to heat, 
which expels the oxygen and muriatic acid. 
It was white, and could not be melted by 
S s % 
