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thin parts of the Juices of peculiar plants, the curd or thick part of which being glutinous and infipid, mayferve them as wax, and the thin part may make their honey. The throat-wort, fpurge, and many other plants, replete with milky Juices, are of this kind, and their Juice, when let out, feparates into curd and whey. But this, though a common law of nature, is not-univerfal; for there are many plants which yield the like milky Juices which do not fepa- rate and break into curds and whey, but coagulate all to- gether into one fimple mafs. The white Juice of the fonchus never feparates, but dries into an uniform cake ; the com- mon red wild poppy bleeds freely with a milky Juice, and the heads or capfules of feed bleed not lefs than the reft of the plant, even after the flower is fallen. This Juice, on "being received into a {hell or other fmall veflel, foon changes its white to a deep yellow colour, and dries into a cake which feems refmous and oily, but no whey feparates from it.
It feems by the experiments on the Juice of the opium let- tuce before mentioned, that thefe milky liquors are of a mixed kind, and compofed of different fluids, of various and perhaps of contrary qualities ; fo that if the curd part be Am- ple and harmlefs, the whey may be a powerful medicine, and fo of the reft : But in thefe which do not feparate in this manner, we are forced to take the whole together, unlefs fome way may be found of feparating them by art. Perhaps the fetting them in wooden veffels, and after a time adding frefh Juice to them, may do it ; and poflibly the adding a little calf's runnet may be able to effecT: it. The tragopogon, or goat's-beard, when wounded, bleeds freely a milky Juice ; it is at firft white, but becomes im- mediately yellow, and after that more and more red ; at length it is wholly of a duflty red. It never feparates but dries ton-ether into one cake, and is oily and refmous, but of an infipid tafte. The great bindweed bleeds freely alfo a white Juice ; the flowers, as well as the ftalks and leaves, affopd this liquor. It is of a ftiarp tafte, and as many of the purging plants are of this clafs, it would be worth trying whether this milk be not purgative.
Thefe Juices, as well as the generality of others which bleed freely from plants, are white like milk, but there are fome of other colours. The -Juice of the great celandine is of a fine yellow; it flows from the plant in the th'icknefs of cream, and foon dries into a hard cake, without any whey feparating from St. Another yellow Juice is yielded by the feed veffels of the yellow centaury, in the month of July, ■when the feeds are full grown. This is of a fine yellow co- lour, and very clammy ; it foon hardens altogether into a cake, no whey feparating from it; it fticks to the fingers like birdlime, and is of the colour of pale amber, and will never become harder than foft wax, if dried in the "{hade ; but if laid in the fun it immediately becomes hard like refin. Thefe cakes burn like wax, and emit a very pleafant fmcll. The great angelica alfo yields a yellowifh Juice on being wounded ; and this will not harden at all, but if kept feveral years will ftill be foft and clammy, drawing out into threads like wax, or half melted refin.
Another kind of Juices, very different from all thefe, are thofe of a gummy nature ; fome of thefe remain liquid a long time, and are not to be dried fooner without the aflift- ance of heat ; the others very quickly harden of themfelves, and are not inflammable. The gum of the Juice ^ of rhu- barb leaves foon hardens, and is afterwards foluble in com- mon water, and fparkles when put into the flame of a can- dle. Thefe two qualities mew that thefe gums have a watery part in them, and they melt alfo in the flame of a candle, and become ductile ; and this fhews that they have alfo the curdy part, though this does not feparate from the whey in drying, as in fome other cafes. Thefe do not fparkle in the flame fo much as fome others which contain more water ; and their not burfting out into an a&ual flame, fhews that they want oil.
The clufters of the common honeyfuckle are full of a liquid gum; they frequently throw this out, and it falls upon the leaves, and retains its own form there ; the red hairs of the fundew are all terminated by large bladders of a thin wa- tery fluid : This is alfo a liquid gum, it fticks to the fingers, and draws out into long threads, and this ftands the force of the fun all day. In the center of each of thefe dew drops, there is a fmall red bladder which ftands immediately on the fummit of the red hair. This is of the nature of the blebs on the leaves and flowers of the St. John's wort, containing a purple Juice which may be fqueezed out of it. ' The pin- guicula, or butter-wort, has alfo fome gummy liquid matter on its leaves. It docs not ftand upon fuch long hairs as that of the fun-dew, but it is in much greater quantity. The hairs of the leaves of thefe two plants ftand on the upper fides of the leaves, and are very thick fet there, while the under fide is fmooth. This is a angularity not obfervable in any other plant, at leaft of our own growth. Vid. Lijler, in Philof. Tranf. N° 224. and Lowtborp's Abridg. vol. 2. p. 696, feq.
Mr. Boyle tells us that the fumigated Juices of plants may be fuccefsfully preferved by adding a fmall quantity of the
white coagulum, made by the pure fpirits of wine and urine'* See the article Offa alba.
Oily Juices. Some plants yield Juices which are of a mani- feftly oily nature, which, being rubbed between the fingers, are not at all clammy, hut make them glib and flippery ; and thefe Juices do not harden at all on being expofed to the air. If the ftalk of elecampane be wounded, there flows out a plain oily Juice fwimming upon a watery one. The ftalks of hemlock alfo afford the fame oily liquor fwimming upon the other ; and the common white mullein, if the leaves are pulled off in the month of June, yields the fame fort of oil very freely along with its watery Juice. The berries of ivy, the bay, juniper, dogberry tree, and the fruit of the olive, when wounded, fhew their oil in the fame manner floating on the watery Juice.
Some of thefe oily Juices, foon after they are let out of the plant, coagulate and harden into a kindofrefm. Our ivy yields fuch a Juice very abundantly ; and the Juice of the fmall purple-berried juniper is of the fame kind, being hard and fat, and not very gummy.
If the bark of the common ivy be wounded in March, there will ooze out a tough and grcafy matter of a yellowifh co- lour; if this be taken up between the fingers, it feels not at all gummy or flicking, but melts in handling into a fort of oil, which in procefs of time hardens and crufts upon the wounds, and looks like brown fugar ; it burns with a lafting flame, and fmells very ftrong. The tops of the wild lettuce, and the leaves growing near the tops, if examined with a magnifying-glafs, fhew a great number of fmall bladders or drops of an oily Juice of a brownifh colour, hardening into a kind of refin ; they are eafily wiped off when of any fize, and are truly an oily Juice hardened a little. It is probable alfo, that the fine blue flower or powder called the bloom, upon the furface of our common plums, is no other than fuch an oily Juice exfudating from their pores in fmall parti- cles, and hardening into a fort of refin. The leaves and ftalks of the common Englifh mercury, are all over covered with fmall tranfparent drops looking like pearls ; and if the plant is taken into the hand, thefe feel rigid and greafy. The leaves of the (linking orach abound alfo with the fame fort of drops, and thefe are only fmall portions of the oily Juices of the plant, which arc continually exfudating through its pores, and harden into thefe refmy pearls. Phil. Tranf. N° 224.
The fap or Juice of trees appears to be very different, ac- cording to the fpecies or genus of the tree, as we find by experiments, or by their fpontaneous exfudations. The ex- travafations of fap in the plum and cherry kind, being all clammy, and hardening into a gum like gum-arabic; and on the other hand, thofe of the vine, the oak, and many other trees, being thin as water. The clamminefs of the fap in trees, feems one of the great things that renders them hardy, and not liable to injuries from cold, c?V. In the hard frofts, thofe trees which have watery Juices pcrifh, and even fplit and cleave of themfelves ; while thofe which have gummy and vifcous Juices efcape. In our gardens the vines crack and burft with the froft, while the plums, cherries, peaches, and other gummy trees, ftand without any damage or danger ; and in the fields no trees fo readily fplit in fevere frofts as the oaks, which though the hardeft wood of all our timber trees, yet has of all the moll thin and watery Juices. The trees which have deciduous leaves, have in general thinner and more watery Juices than the evergreens ; to the freezing of thefe, or their decay from want of due heat, and other accidents, is owing the decay and fall of thofe leaves, while the others remain in their places, though not encrea- fing, or no new ones growing, the Juices remaining unal- tered, though ftagnated in the veffels, and fafe from injury, though waiting the fun's heat to put them in motion. The earlier or later germination of trees and plants of different kinds, is probably owing alfo to the fame caufe. The thin- neft Juices, as they are'fooneft injured by cold, fo they are probably fooneft influenced alfo by heat ; and that warmth may make them move, and prepare the plant for growing, which could fcarce begin to attenuate the tough and gummy ones. Phil. Tranf. N° 165. See the article Sap.
Concrete Juices, in mineralogy, a name given by many au- thors to fuch fubftances found in the bowels of the earth, as have once been in a ftate of fluidity, and are capable of be- ing rendered fluid again by art, by means of heat, moifture, or other common agents.
Others apply the word concrete to all thofe fubftances which may be feparated from fluids by chemical operations, whe- ther they are afterwards foluble in them again or not ; fuch are the particles of fpar feparated from water by a flow dif- tillation, and remaining at the bottom of the veflel. The concrete Juices of the earth are fuppofed to be the prin- cipal things which give the virtue to mineral waters ; for thofe which receive no concretion, and are only mingled with the waters in their paffage through that part of the earth where they are evaporated, on the waters being expofed to the air, tho' they may give a brifknefs to it, while entire in it, yet are not to be fuppofed to give the principal virtues. Thefe fluid and volatile Juices all fly off in the analyfes of the wa- ters*
