Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/257

 P L A

P L A

The fpecies of platanus, enumerated by Mr. Tournefort, are thefe : I. The true oriental platanus. z. The occidental or Virginian platanm. Tourn. Inft. p. 590.

PLANKS, in a fhip, are the timbers which go fore and aft on each fide of the fhip, whereon lie the beams of the firft orlop.

Garboard Plank, in a fhip. See Garboard.

PLANT (Ojd.)— The greater the degree of heat given to plant: to a certain degree in the natural way, the fooner they go through the whole bufmefs of their ftu&ficatron. In the northern regions, where there are but a few fummer months, the herbs all are ripened in them in a furprizing manner : in Lapland, for inftance, where the greater part of the year is fubjea to intenfe and inceffant frofts, and for a conflderable time to the entire abfence of the fun, the fummer feafon affords an exceffive heat for two months, the fun never fetting in all that time. This feafon comes on toward the latter end of June, and the grafs and other herbs then firft begin to appear in their young (hoots above the ground, and the trees bud ; but all vegetation is, after this, carried on with fuch fpeed, that in a fortnight the flowers of the herbs and trees are expanded, and tire leaves of their full fize and maturity. Scbcffir's Htft. Lapon.

The virtues of plants are very variable ; a change of climate will alter or deftroy them, as we fee in many of the medicinal plants of other countries, brought over hither, which, tho' they feem to flourifli with us, never poffefs their virtues in the fame degreee as in their native climate. The bodies of different animals alfo render the effea of the fame plant dif- ferent : the tithymals or fpurges are all of them very violent cathartics, when taken by us ; but yet they are eaten by goats and feveral other animals without hurt, or without any purgative effea, and feem to give them a particular (hare of vigour and fpirits. The fifb. are, on the other hand, more ftrongly af- fefled by it than we are ; for the juice made into pafte with flower and honey, poifons, or at leatt intoxicates them fo, that they may be taken out of the water with one's hand. Bitter almonds are of no ill confequence to us, yet they kill all forts of birds. DiJIande's Trait. Phyfiq.

Imperfelt Plants, in botany, a name given to thofe plants which feem to want both flower and feed. Thefe were once a very large tribe of plants, but the more accurate obfervations of the moderns have proved, that the moft of thefe plants really contained feeds, and thofe very numerous, tho' fo fmall as not to appear obvious to the naked eye : and probably the farther difcoveries of the microfcope will in time leave us no one plant deferving the appellation of impirfia. In Mr. Ray's time, many whole genera of plants were efteemed imperfecf ; but he includes the feveral kinds he calls fo, under three gene- ral heads : 1. The fubmarine. 2. The fungufes. And, 3. The moffes. Tho' many of all thefe kinds have by later authors been (hewn to have true feeds, and it is fcarce to be doubted of the reft. Ra/s Synopf. Stirp. Brit. p. 1.

Flowering o/Plants. See the article Flowering.

Jnalyfis of Plants. The common method of attempting the analyfis of plants, by common diftillations, gave hopes that it would prove very ufeful in determining their virtues ; but ex- periment (hewed it to fail of this intent, fince the wholefome plants and the poifonous ones afforded by this means much the fame fort of principles ; and on the whole, thefe appeared in a great meafure to be creatures of the fire rather than parts of the fubjea. This fet Mr. BOulduc of the Paris academy upon trying, whether there might not be fome way invented at once more fimple and more certain ; and with this view he attempted to examine the juices and decoaions of feveral plants, to find their effential falts, which had not been pro- cured in their natural (late by the chemical trials. The plant this gentleman chofe as the fubjea of his experiments in this view, was the common borage.

Firft, he made a large quantity of a decoaion of borage ; this he divided into three equal parts : the firft of thefe he evaporated to a pellicle, or to the confidence of a fyrup ; it was then of a blackifh colour, and was charged with a great quantity of oily particles. This being fet by for fome days in a warm time of the year, covered itfelf with a thick (kin, which was again covered by a mouldinefs. When this (kin •was removed, there appeared underneath a large quantity of chryftals, in fine (lender filaments like needles, mixed among a large quantity of other cryftals, which were fmall, and of no regular figures ; all thefe were fwimming in a liquor of the thicknefs of a fyrup. Thefe long cryftals being taken out of the liquor, and laid upon a hot iron, took fire, and flamed in the manner of falt-petre when mixed with any fulpbureous fubftance ; and, in truth, this was a falt-petre, yet loaded with the oily matter of the decoaion.

Here, therefore, is a clear proof, not only of the nitrous acid being in this plant, but of plain nitre itfelf; for, on pouring oil of tartar on a folution of this fait, there was no precipita- tion made of any fubftance whatever; which would have been the cafe, had there been in this (late any earthy matter for its bans.

The fecond portion of this decoaion was diverted of its oil by means of lime, and then evaporated to a light pellicle over a very gentle heat. This was fet by to reft for fome days, and

finer and more perfeft cryftals were found, (hot in the form of needles in it : thefe were truly nitrous, and occupied the upper part of the liquor ; below thefe there were a great number of other cubic ones, which were eafily known to be cryftals of fea fait.

I he long cryftals of this operation took (ire on a lighted char- coal, and appeared plain nitre; and the others, when dry, cre- pitated in the (ire exaflly in the manner of fea fait : and when a folution of them was poured upon a folution of fllver, made in fp rit of nitre, it immediately occafioned a white curd to ap- pear, which being feparated, waffled, and put to the fire, became a true luna cornea, being* tranfparent and eafily cut with a knife. Here, therefore, are plain proofs of nitre and fea fait in this plant. Mem. Acad. Scienc. Par. J734. The third portion of the decoaion was poured upon fome frefh wood afhes, and being afterwards evaporated to a pel- licle, and fet by for fome days, there was found in this more nitre than in any of the others ; and that whiter and more clear, the others being ufually coloured brownifh or reddifll by the decoaion. The occafion of this feems to be, that part of the nitrous acid, which in the other experiments neither joined with any earthy matter, nor with the fatty matter of the de- coaion, mixed with the falts of the lixivium, made by pour- ing the liquor which contained it on wood afhes, and thus yielded a much larger quantity of faltpetre than before. The fatty fubftance which covered the 'firft decoaion being dried, was found to contain a great quantity of nitre, which it had not fuffered to fhoor, or form itfelf into cryftals : this dried cruft being laid on a burning charcoal, took fire in the fame manner as if nitre and powder of charcoal had been thrown into a crucible made red hot.

The falts of the plant being thus obtained from its decoaion, it was determined to try whether the plant remaining after the decoclion had any more to yield. To try this, it was gently dried in a (hade, and burned in a covered veffel to a black coal, and afterwards, in an open (ire, to afhes. Of thefe allies there was made a lixivium in the common way, in order to be evaporated for the fait : this lixivium being mix- ed with fyrup of violets, fcarce at all altered it from its blue colours, only juft bringing on a faint greenifhnefs, which foon went off again, and left the fyrup of as fine a blue as before; this made it evident, either that there was very little alkali fait there, or elfe that it was blended with falts of fome other kind, which altered its effeas : and this proved to be the true ftate of the matter on farther experiment, for, evaporating the lixi- vium to a pellicle, there very foon (hot in it regular and beautiful cryftals of a fait, having all the charaaers of tartarum vitriolatum. A fecond evaporation of the lixivium afforded more of the fame fait, but in fmaller cryftals. Evaporating the liquor to about half its quantity, and fetting it again to (hoot, there appeared plain cubic cryftals of fea fait ; which being ftrialy examined, were found to be perfea fea fait, no way altered, but having flood the force of the calcination. After thefe falts had been feparated from the lixivium, it changed fyrup of violets immediately to a beautiful green, which colour it always retained.

It is evident from thefe experiments, that this plant affords four different kinds of falts, viz. nitre, fea fait, tartarum vi- triolatum, and the common fixed alkali ; and it is hence no trivial observation, that the three mineral acids are found here all in one plant. It is not to be fuppofed, indeed, that the tartarum vitriolatum was aaually in the plant in that form, but it is very evident, that the vitriolic acid did always exift there, ready to form it ; but that being, before the calcination, enveloped in the oily matter of theplant, it was not eafy to difcover it either by its properties or effeas : but as foon as the oil was diflipated by fire in the calcination, the vitriolic acid immediately became free, and finding the alcaline fait of the plant, or its fixed nitre, which had remained after the de- flagration, it immediately united with it, and formed a tarta- rum vitriolatum in the fame manner as a tartarum vitriolatum may be made from fait of tartar and common fulphur, afiei the oily or inflammable part of the fulphur is burnt away.

It is not only this plant that yields a vitriolated tartar from a lixivium with its afhes, but great numbers of others of the aromatic and bitter kinds : whence it appears, that the vitrio- lic acid, tho' the moft fixed of all the mineral acids, yet raifes itfelf into the juices of a great number of plants; and on the refutt of great numbers of experiments, it appears, that there are very few plants which yield a pure alkaline fait, perhaps fait of tartar is the only perfectly pure known alkali of this kind, which retains no portion of any other fait. AJbes of Plants. The aftiesof a plant carefully prepared, re- tains its exafl form till difturbed by accidents. The way of preparing them is this: Take a whole plant which has been ufed for the diftillation of the oil, water, &c. lay it evenly upon a flat plate of iron, and place this on a clear fire, that no fmoak may prevent the fuccefs of the operation ; continue and raife the fire, till the whole fubftance of the plant appears per- fealy ignited. There firft arifes a light fmoak from it, this gradually becomes darker, and at length as black as pitch ; the fmell of burning increafesas the fmoak increafes, at length the fmoak breaks out into flame, and then the fmell in a great

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