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Homberg is the pure falt, falt the principle, ?n it" self fimilar and unisorm, but never found alone. And although this principle be called the falt of the earth, yet it Mould seem it may more properly be called the salt of the air, since earth turned up and lying fallow receives it from the air. And it should seem that this is the great principle of vegetation, derived into the earth from all forts of manures, as well as from the air. The acid is allowed to be the cause of sermentation in all fermented liquors. Why therefore, may it not be supposed to serment the earth, and to constitute that fine penetrating principle, which introduces and assimilates the food of plants, and is so sugitive as to escape all the filtrations and perquisitions of the most nice observers?

127, It is the doctrine of Sir Ifaac Newton and Monsieur Homberg, that, as the watry acid is that which renders falt soluble in water, so it is that fame which joined to the earthy part makes it a falt. Let it therefore be considered, that the organs (d) of plants are tubes, the filling, unfolding, and distending whereof by liquors, doth constitute what is called the vegetation or growth of the plant. Bat earth it selt is not soluble in water, so as to form one vegetable fluid therewith. Therefore the particles of earth must be joined with a watry acid, that k, they must become skits in order to dissolve in water; that so, in the Iforrrr of a vegetable juice, they may pass through the ..strainers and tubes of the root into the ttody of the pfant, swelling and distending icVpanrts^od ftrgahs, thai is, increasing it's bulk. Therefor* the Vegetable matter of the earth is in eSict esarth tfhartged into sol*. And to render earth

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fertile, is to cause many of it'i particles to asturne a faline form. . , . '' .

- 128. Hence it is observed, there are more salts in the root than in the bark, more &ha in vegetables during the spring, than in the antuara* or winter* the crude klrne juices being in the summer months partly evaporated, and partly ri~>. pened by the action and mixture of light. Hence also it appears, why the dividing of earth, so as to enlarge it's surface, whereby it may admit more acid from the air, is of such ufe in promoting vegetation. And why aihes, lime, and* burnt clay are found so profitable manures, fire being in reality the acid, as is proved in the sequel (a). Marls also and shells are useful, foras-< much as those alcaline bodies attract the acid, and raise an effervescence with it, thereby promoting a sermentation in the glebe. The excrements of animals and putrid vegetables do in Jike manner contribute to vegetation, by increasing the falts of the earth. And where fallows are well broken,: and lye long to receive the acid of the air into all their parfs this alone will be sufficient to change many terrene particles into salts, and consequently -. render them soluble in water, and therefore fit aliment for vegetables. .

129. The acid, faith Homberg, is always joined to some sulphur, which determines it to this or that species, producing different falts, as it is the vegetable, bituminous, or metallique sulphur. Ev ven the alcaline, whether volatile or iixivial salts, are supposed to be nothing but this fame acid strictly detained by oil and earth, in spight of the extreme force of sire, which iodgeth in them, without being able to dislodge some remains of th» acid.

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; 130. Salts, according to fir Ifaac Newton, arc dry earth and watery acid united by attraction, the acid rendering them soluble in water (f). He supposeth the watry acid to flow round the terrestrial part, as the ocean doth round the earth, being attracted thereby, and compares .each particle of falt, to a chaos whereof the innermost part is hard and earthy, but the surface soft and; watery. Whatever attracts and is attracted most strongly is an acid in his sense.

131. It seems impossible to determine the figures! of particular falts. All- acid solvents together with the dissolved bodies are apt to shoot into certain figures. And the figures, in which the fossil falts crystallize, have been supposed the proper natural' fiiapes of them and their acids. But Homberg Jiath clearly shewed the contrary: forasmuch as the lame acid dissolving different bodies, assumes dis-. fcrent shapes. Spirit of nitre, for instance, having dissolved copper, shoots into hexagonal crystals; the fame having dissolved iron, shoots. into irregular squares; and again, having dissolved stiver, forms thin crystals of a triangular figure. . v iy2. Homberg-nevertheless holds in general, that acids are shaped Uke daggers, and alcalies like sheaths: and that moving in the fame liquor, the daggers;run into the sheaihs fitted to receive them, withisnch violence as jfa raise that efservescence observed in the mixture of acids and alcalies. But k feems very disficult to conceive, how, or why the Bicre configuration of daggers and sheaths, floating' ib:the fame liquor, should cause the fornaer to rush with such vehemence* and direct their points so aptly into the latœr, any more than a parcel- of spigots iuielifolsets floating together in thc/ame water, sliould rush one into the other. ...

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133. It should seem rather, that the vehement attraction which Sir Ifaac Newton attributes to ali acids, whereby he supposeth them so rush towards, penetrate, shake, and divide the most solid bodies, and to serment the liquid of vegetables, could better account for this phænomenon. It is in this attraction, that fir Ifaac placeth all their activity, and indeed it should seem, the figures of falts were not of such efficacy in producing their efsects, as the strong attractive powers whereby they are agitated and do agitate other bodies. Especially if it be true (what was before remarked) that lixivious salts are alike purgative, whatever may be the lhape of their angles, whether more or less acute or obtuse.

134. Sir Ifaac Newton accounts for the watery acids making earthy corpuscles soluble in water, by supposing the acid to be a mean between earth and water, its particles greater than those of water, and less than those of earth, and strongly to attract both. But perhaps there is no necessary reason for supposing the parts of the acid grosser than the parts of water, in order to produce this effect; may not this as well be accounted for, by giving them only a strong attraction or cohesion with the bodies to which they are joined?

j 35. The acid spirit or falt, that mighty instrument in the hand of nature, residing in the air, and difsused throughout that whole element, is discernible also in many parts of the earth, particularly in fossils, such as sulphur, vitriol, and alum *, it was already observed from Homberg, that this acid is never found pure, but hath always sulphur joined with it, and is classed by the disserence of its sulphurs, whether mineral, vegetable, or animal.

136. 9altsare vulgarly reckoned the most active of chemical principles. But Homberg derives all' their activity from the sulphurs joined with them, from which also, as hath been said, he derives all their kinds and disserences (g). Salt, water, oil, and earth seem to be originally the fame in all vegetables. All the difference, according to the chemists, ariscth from a spirit residing in the oil, called the Rector or Archæus. This is otherwise called by chemists, ens primum, or the native spirit, whereon depend, and wherein are contained, the peculiar flavour and odour, the specific qualities and virtues of the plant.

137, These native spirits or vegetable souls are all breathed or exhaled into the air, which seems the receptacle as well as source of all sublunary forms, the great mass or chaos which imparts and receives them. The air, or atmosphere, that surrounds our earth, contains a mixture of all the active volatile parts of the whole habitable world, that is, of all vegetables, minerals, and animals. Whatever perspires, corrupts, or exhales, impregnates the air; which, being acted upon by the solar fire, produceth within itself all sorts of chemical operations, dispensing again those falts and spirits in new

fenerations, which it hadreceived from putrefactins.

138. The perpetual oscillations of this elastic and restless element operate without ceasing, on all things that have life, whether animal or vegetable, keeping their fibres, vessels, and fluids in a motion always changing; as heat, cold, moisture, dryness, and other causes alter the elasticity of the air. Which accounts, it must be owned, for many effects. But there are many more which must be derived from other principles or qualities in the air. Thus iron and copper are corroded and gather rust in the air, and bodies of all sorts are dissolved or corrupted,

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