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preferve a long time. When they are to place the ends or pufls in the ground, they, on the lame principle, burn them a little, that the volatile falts, which would eafily be con- fumed by the moifture of the earth, may be, in feme degree, liquated and blended together by the heat, and be rendered fb much the more fixed, as to be lefs eafily affected by external accidents. Ship- builders, in fomc places, for the fame rca- fon, burn flight)}' all the timber that is to make the bottom of the vefTcl, or fuch part of it as is to be under water. Another very familiar inftance of the blending the two vola- tile fait s s naturally given to all vegetables, is in the formation* of foot. When wood is burning, there afcends from it a foroak ; In this fmonk the two volatile falts of the wood are contained, and they coagulate one another into that body which we call foot, and from which they may be again fe- parated by art, and rendered vifible diftinctly. Thefe falts continue afcending, and forming foot, till the wood is re- duced to afhes; and what remain of them toward this con- clufiun of the operation of the fire, are blended together by it, and make what we call the common fixed alkali, a fait eafily wafhed out by water.

The formation of the fixed fait being thus owing to the mix- ing together of the two volatile ones found in the plant, it is eafy to conceive why we obtain more of it from found wood, than from fuch as is rotten, and more from frefh plants, than from fuch as have been dried. If the fixed fait exifted as a fixed body in the vegetable, it could not be affe&ed by the evaporation of the water in drying, or by the evaporating of whatever elfe evaporates in the decaying of wood. But as "the fait itfelf, or its two conftituent parts, though called fixed by us, and rendered fo by fire, are really volatile while in the plants, it is no wonder that, being refoluble by the fait of the air, they are carried oft in the drying, and much more fo in the decaying of wood ; for the air, in this cafe, evidently pe- netrates all its parts ; and hence it is, that as dry plants yield lefs fixed fait than frefh ones, fo the fame wood, which, while found, would have yielded a very large quantity of fait, yet being rotten, yields fcarce any at all, though the fame procefs is obferved in burning it.

We are indebted to the pains of Dr. Cox for a method of pro- curing a volatile fait from plants, a thing of ccnfiderable ufe in medicine, though fo much out of the common road of the chemical analyfifes that it was not difcovered till about eighty years ago, and foon after reduced to practice, in a regular manner, by that phyfician.

The method is this: A quantity of the leaves of any plant are to be carefully {tripped from the ftalks in fummer, in dry weather; lay them in a heap, prefied bard together, and they will foon ferment and heat, and will be 'reduced to a pulpy fubfhnce. This is to be rolled into little balls, and put into a retort, and diftilled ; it will yield a thick liquor, of a ffrong fmell, and a large quantity of a black oil, of a btilfamic con- iiftence. The liquor is to be feparated from the oil, and di- ftilled over again in a tall glafs cucurbit ; a volatile fpirit arlfes ; this is to be rectified two or three times more, and then is not to be diliinguifhed from the fpirit of harts-horn, urine, or other animal fubftances, by any trials. Philof. Tranf. N°- ici. p. 4.

All plants that have ever been tried in this manner, yield this volatile fait diflolved into the form of a fpirit; and the very lowed clafs of plants, the moffes, and common grafs, yield it as well as any other. And it is remarkable, that the vefFels in which thefe operations arc performed, have afterwards a fmell like muik, which all the cleanfmg in the world, and even the expofiug them to the air, does not well clear them of. The caput mortuum left in the vefTtds is much lefs in quantity than in the common diftillations of a like quantity of the fame plant ; and if the plants have not been fufficiently fer- mented before the diftillation, there remains, after the firft reel: ificat ion of the fpiritucus' liquor, a four water. The volatile fait, thus obtained, isconiiderably more in quantity than the effential or the incinerated fait would have been in the common ways of preparing them; but thofe plants which yield maft fixed fait, always yield molt volatile fait this way. And thefe volatile falts, when well rectified, do not differ from one another, though made from ever fo different plants ; but this is not wonderful, fince the fixed falts alfo, and the vinous fpirits of all plants are alike, when reduced to the fame degree of perfection and purity. The herb, as it ferments, affords its natural fmell at firft very ftrongly ; after that it yields a mixed fmell, between its own natural fceht and an urinous one ; and at the end, when it is nearly ready for diftillation, the fmell becomes urinous. In this operation, the urinous fpirit and fait come over chiefly toward the end of the diftil- lation, and are fecn in form of white clouds, iifuing very faff out of the neck of the retort, and cendenfing on the fides of the receiver into little rivulets, or winding {breams of water. Sage, winter favoryj and fome other of the aromatic plants, yield thin volatile fait, on the firft diftillation, in a dry form, coating over the infide of the receiver on the upper part, and clogging the neck of the retort; and faffron, in digeftion with fpirit of wine, has been found to } ield its fait in the fame dry form.

The oils procured in this manner from fermented plants Su ppj,. Vol. II.

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partake nothing of the nature of the peculiar plant, hut are alike from all ; they are thick as tar, anil fcetid. If the plant be not well fermented, indeed; the oil will be clear, and leave the fmell and virtues of the plants : But this is an error in the procefs, and this oil comes at firft ; whereas the proper oil of this procefs comes not till the laff, with the fait. Thofe plants which, in the common way of diftillation, yield molt efler.tial oil, j ield alfo moil of this black thick oil in this pro- cefs. .

I he fatty, moilr, and infipid herbs, ferment much quicker than the other kinds : They become extremely hot in this fer- mentation, and lofe their peculiar qualities in it ; the fpurge loles its milkyuefs, and the celandine its tinging quality ; and the juices of thofe which are naturally the molt acrid and (harp, become little more fo than thofe of others. The flanking plants, fuch as the atriplex ' olida, are as fweet in this pro- cefs as any other ; and it is particular, that the monk's rhu- bard, and fome others, which are as inodorous as any plant can be, in their natural (late, are as fcetid as human excre- ments, under this treatment : And it is remarkable, that the very greateft heat of the fermentation of thefe plants, does not preveiu their being frored with a fort of maggots, which (warm in great numbers in thofe parts of the fermented rriafs, where the heat is fo great, that a pcrfon cannot bear his hand in it.

It is to be confidered, whether thefe animals may not afford the volatile fait attributed to the plants. The doctor does not feem to have confidered this ; but as they are faid to be Very numerous in the mafs, it wijl be very neceflary to try the ef- fect of a diftillation of fomeof this fermented matter, without thefe infects ; which might be done by covering the whole from the accefs of flics: For though the Doftor fcems to think they are equivocally generated there, it is certain that they owe their origin entirely and only to the eggs of flies. The Doctor fecms. to think they will of themfelves yield 1 no volatile fait or fpirit ; but this is fo different from the nature of animal bodies in general, that it may be this opinion was founded on too flight a trial. If the external air be excluded from plants, they will not ferment, and if they are put into a long-necked glafs,- and left open, they will, in a few weeks, become of a mucilaginous nature ; and after Handing a year in this manner, they will yield a large quantity of urinous fait or fpirit, but not a drop of oil. - -

Some 'mofles, and other of the plants ufually called imperfect, yield a volatile fait on diftillation, ' without preVious'putre- • faction; and fome' feeds, though in themfelves infipid to. the tafte, have the fame quality.

All thefe fpirits and falts have the fame properties and effects with the fpirits of harts-horn apd urine. They change fyrup of violets, and man'y other vegetable tinctures green. They are diaphoretic, ' diuretic, and deobft ruent, and contrary in their nature to acids. They precipitate all metals diffolVed in acids, by breaking the force of thofe acids, and when highly rectified, and mixed with fpirit of ; wine as highly rectified, they make the offa alba of Helmont like all other volatile alkali fpirits ; they unite with acids, and thereby become, ar- moniac or neutral falts. Phil. Tranf. N°. rbl. p. 7. Chemical experiments abundantly prove that volatile falts are obtainable from ail kinds of land animals, the am- amphibious and fubterraneous tribes, birds, fifh, and reptiles, from alkaline vegetables alfo without putrefaction, and from all other vegetables, after putrefaction, as alfo from foot, horns, hoofs, and all refufe animal and vegetable matters, fuch as the pith of horns, urine, the blood of flaughter-houfes, C5"c. and thefe as pure and perfect as from harts-horn; and this affords a hint for the making volatile alkalies and fal ar- moniac cheap in England. Shaw's Lectures, p. 168. The fhootings of volatile falts are not limited like thofe of the fixed and common falts, to any determinate figures, but, by various accidents are thrown into a great variety of pleafing forms. Fanciful people have fuppnfed the fhootings of fait of hartfhorn, in the tops of the veffels ufed in fubliming it, to refemble the horns of the deers ; and that of vipers, to affume. the figure of little crawling ferpents ; but all this is imaginary, and the things from which the falts are obtained have no power to determine their forms, which are governed by more vague principles ; fuch as the peculiar degree of heat, the tempera- ture of the external air, and many other the like uncertain principles.

We have, in the Philofophical Tranfactions, an account of a whole foreft of moff elegant trees painted in perfpective, in the head of a veffel, by thefe bodies. The fubftances em- ployed were fal armoniac and pot-afhes ; thefe were mixed in equal quantities, and put into a tall glafs body, which being placed in fand, immediately on the approach of the heat, a large quantity of the fait was fublimed in flowers in the com- mon way ; this was a procefs from which nothing particular could be expected ; but after fome time the fublimed fait be- gan to affume a regular form, and the head of the cucurbit, which was very large, was filled with the reprefentations of trees fo perfect and elegant, that a foreft, delineated by the ableft hand, could fcarce come up to it. The figures, though externally numerous, yet were very re- gular, and all reducible to three kinds ; the pine, the fir, and 5 M ens