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Homberg is the pure salt, salt the principle, in it self similar and uniform, but never found alone. . And although this principle be called the salt of the earth, yet it should 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 sorts of manures, as well as from the air. The acid is allowed to be the cause of fermentation in all fermented liquors. Why therefore, may it not be supposed to ferment the earth, and to constitute that fine penetrating principle, which introduces and assimilates the food of plants, and is so fugitive as to escape all the filtrations and perquisitions of the most nice observers ?

127. It is the doctrine of Sir Isaac Newton and Monsieur Homberg, that, as the watry acid is that which renders salt soluble in water, so it is that same 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. But earth itself is not soluble in water, so as to form one vegetable Auid therewith. Therefore the particles of earth must be joined with a watry acid, that is, they must become salts in order to diffolve in water ; that so, in the form of a vegetable juice, they may pass through the strainers and tubes of the root into the body of the plant, swelling and distending it's parts and organs, that is, increasing it's bulk. Therefore the vegetable matter of the earth is in effect earth changed into falt. And to render earth

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fertile, is to cause many of it's particles to assume a faline form.

128. Hence it is observed, there are more falts in the root than in the bark, more salts in vegetables during the spring, than in the autumn or winter, the crude saline juices being in the summer months partly evaporated, and partly ripened 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 use in promoting vegetation : And why ashes, 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, forasmuch as those alcaline bodies attract the acid, and raise an effervescence with it, thereby promoting a fermentation in the glebe. The excrements of animals and putrid vegetables do in like manner contribute to vegetation, by increasing the salts of the earth. And where fallows are well broken, and lye long to receive the acid of the air into all their parts; this alone will be sufficient to change many terrene particles into falts, and consequently render them soluble in water, and therefore fit aliment for vegetables.

129. The acid, saith Homberg, is always joined to some sulphur, which determines it to this or that species, producing different salts, as it is the vegetable, bituminous, or metallique sulphur. Even the alcaline, whether volatile or lixivial salts, are supposed to be nothing but this fame acid strictly detained by oil and earth, in spight of the extreme force of fire, which lodgeth in them, without being able to disodge some remains of the

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130. Salts, according to sir Isaac Newton, are 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 doch round the earth, being attracted thereby, and compares each particle of salt, 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 salts. All acid solvents together with the dissolved bodies are apt to shoot into certain figures. And the figures, in which the foffil salts crystallize, have been supposed the proper natural thapes of them and their acids. But Homberg hath clearly shewed the contrary : forasmuch as the fame acid diffolving different bodies, assumes different shapes. Spirit of nitre, for instance, hav. ing dissolved copper, shoots into hexagonal crystals ; the fame having uifolved iron, shoots into irregular squares; and again, having diffolved silver, forms thin crystals of a triangular figure.

132. Homberg nevertheless holds in general, that acids are shaped like daggers, and alcalies like sheaths : and that moving in the same liquor, the daggers run into the sheaths fitted to receive them, with such violence as to raise that effervescence observed in the mixture of acids and alcalies. But it feems very difficult to conceive, how, or why the mere configuration of daggers and sheaths, floating in the same liquor, should cause the former to rush with such vehemence, and direct their points so aptly into the latter, any more than a parcel of spigots and foffets floating together in the same water, hould rush one into the other. (f) 127.

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133. It should seem rather, that the vehement attraction which Sir Isaac Newton attributes to all acids, whereby he supposeth them to rush towards, penetrate, shake, and divide the most solid bodies, and to ferment the liquid of vegetables, could better account for this phænomenon. It is in this attraction, that Sir Isaac placeth all their activity, and indeed it should seem, the figures of salts were not of such efficacy in producing their effects, 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 shape of their angles, whether more or less acute or obtuse. ..134: Sir Isaac Newton accounts for the watery acids making earthy corpuscles soluble in water, by supposing the acid to be a nean 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 ?

135. The acid fpirit or falt, that mighty instrument in the hand of nature, residing in the air, and diffused 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 difference of its sulphurs, whether mineral, vegetable, or animal. . 136. Salts are 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 differences (8). Salt, water, oil, and earth seem to be originally the same in all vegetables. All the difference, according to the chemists, ariseth from a spirit residing in the oil, called the Rector or Archæus. This is otherwise called by chemists, ens primum, or the native fpirit, whereon depend, and wherein are contained, the peculiar favour 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 salts and spirits in new generations, which it had received from putrefactions. .

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 Auids 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 diffolved or corrupted, (8) 129.

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