IRi 



1RI 



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, invi- 

 gorates the whole animal frame. But 

 sudden and excessive joy is often as inju- 

 rious as the operation of either grief or 

 terror, and there are a thousand instances 

 on record, in which the precipitate com- 

 munication of unexpected good news has 

 proved fatal. 



IPECACUANHA. See MATERIA ME- 

 PICA, 



IPOMOEA, in botany, a genus of the 

 Pentandria Monogynia class and order. 

 ^Natural order of Campanacex. 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- 

 leaved ipomoea, is an annual plant, rising 

 with oblong, broad seed leaves, which re- 

 main a considerable time before they fall 

 off; stems slender, twining, rising by 

 support to the height of eight feet, send- 

 ing outseveral side branches, which twine 

 about each other. The flowers come out 

 singly from the side of the stalks, on 

 glender 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 ap- 

 pearance. 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 peren- 

 nial weak plant requiring support, rising 

 twelve feet in height, having 1 large knots 

 at each joint, with oval lanceolate smooth 

 leaves; stems very diffused, branching 

 out on every side ; flowers terminating in 

 slender loose panicles, covered with a sil- 

 ky down, of a pale yellow colour. Na- 

 tive of Jamaica, and other islands in the 

 West Indies. 



IRIDIUM Mr. Tennant, on examining 

 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, 

 pever before noticed, which he has named 

 mdium and osmium. The former of these 



was observed soon after by Descostils, 

 and by Vauquelin. 



To analyse the black powder, Mr. Ten- 

 nant 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 brownisl* 

 yellow colour, but much of the powder 

 remained undissolved. This digested in 

 muriatic acid gave a dark blue solution, 

 which afterwards became of a dusky olive 

 green, and finally, by continuing the heat, 

 of a deep red. The residuum being treat- 

 ed as before with alkali, and so on alter- 

 nately, 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 os- 

 mium, with a small proportion of indium, 

 which separates spontaneously in dark, 

 coloured thin flakes, by keeping it some 

 weeks. 



The acid solution contains likewise 

 both the metals, but chiefly iridium. By 

 slow evaporation it affords an imperfectly 

 crystallized mass ; which being dried on 

 blotting-paper, and dissolved in water, 

 gives by evaporation distinct octaedral 

 crystals. These crystals, dissolved in wa- 

 ter, produce a deep red solution, inclin- 

 ing to orange. Infusion of galls occasions 

 no precipitate, but instantly renders the 

 solution almost colourless. Muriate of tin, 

 carbonate of soda, and prussiate of pot- 

 ash, produce nearly the same effect. Am- 

 monia precipitates the oxide, but, possi- 

 bly from being in excess, retains a part in 

 solution, acquiring a purple colour. The 

 fixed alkalies precipitate the greater part 

 of the oxide, but retain a part in solu- 

 tion, this becoming yellow. All the me- 

 tals that Mr, Tennant tried, except 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 oyxgen and muriatic 

 acid. It was white, and could not be melt- 

 ed by any heat Mr, Tennant could em- 

 ploy. It did not combine with sulphur, 

 or with arsenic. Lead unites with it ea- 

 sily, but is separated by cupellation, leav- 

 ing the iridium on the cupel as a coarse 

 black powder. Copper forms with it a 

 very malleable alloy^ which, after cupella- 

 tion, with the addition of lead, leaves a 

 small proportion of the iridium, but much 

 less than in the preceding instance. Silver 

 forms with it a perfectly malleable com- 



