fertile, is to cause many of its particles to affume a faline form. more 128. Hence it is obferved, there are falts in the root than in the bark, more falts in vegetables during the fpring, than in the autumn or winter, the crude faline juices being in the fummer months partly evaporated, and partly ripened by the action and mixture of light. Hence alfo it appears, why the dividing of earth, fo as to enlarge its furface, whereby it may admit more acid from the air, is of such use in promoting vegetation: And why afhes, lime, and burnt clay are found fo profitable manures, fire being in reality the acid, as is proved in the fequel (a). Marls alfo and fhells are useful, forafmuch as thofe alkaline bodies attract the acid, and raise an effervefcence 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 falts 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 fufficient to change many terrene particles into falts, and confequently render them foluble in water, and therefore fit aliment for vegetables. 129. The acid, faith Homberg, is always joined to fome fulphur, which determines it to this or that fpecies, producing different falts, as it is the vegetable, bituminous, or metallic fulphur. Even the alkaline, whether volatile or lixivial falts, are fuppofed to be nothing but this fame acid ftrictly detained by oil and earth, in fpight of the extreme force of fire, which lodgeth in them, without being able to diflodge fome remains of the acid. (a) 202. 130. Salts, 130. Salts, according to Sir Ifaac Newton, are dry earth and watery acid united by attraction, the acid rendering them foluble in water (f). He fuppofeth the watery acid to flow round the terreftrial part, as the ocean doth round the earth, being attracted thereby, and compares each particle of falt, to a chaos whereof the innermoft part is hard and earthy, but the furface foft and watery. Whatever attracts and is attracted moft ftrongly is an acid in his fenfe.. 131. It feems impoffible to determine the figures of particular falts. All acid folvents together with the diffolved bodies are apt to fhoot into certain figures. And the figures, in which the foffil falts crystallize, have been fuppofed the proper natural fhapes of them and their acids. But Homberg hath clearly fhewed the contrary: forafmuch as the fame acid diffolving different bodies, affumes different fhapes. Spirit of nitre, for inftance, having diffolved copper, fhoots into hexagonal crystals; the fame having diffolved iron, fhoots into irregu lar fquares; and again, having diffolved filver, forms thin cryftals of a triangular figure. 132. Homberg nevertheless holds in general, that acids are shaped like daggers, and alcalies like fheaths: and that moving in the fame liquor, the daggers run into the fheaths fitted to receive them, with fuch violence as to raise that effervefcence obferved in the mixture of acids and alkalies. But it feems very difficult to conceive, how, or why the mere configuration of daggers and sheaths, floating in the fame liquor, fhould cause the former to rush with fuch vehemence, and direct their points fo aptly into the latter, any more than a parcel of fpigots and foffets floating together in the fame water, fhould rush one into the other. (f) 127. 133. It 133. It fhould feem rather, that the vehement attraction which Sir Ifaac Newton attributes to all acids, whereby he fuppofeth them to rush towards, penetrate, fhake, and divide the moft folid bodies, and to ferment the liquid of vegetables, could better account for this phænomenon. It is in this attraction, that Sir Ifaac placeth all their activity, and indeed it should feem, the figures of falts were not of fuch efficacy in producing their effects, as the strong attractive powers whereby they are agitated and do agitate other bodies. Efpecially if it be true (what was before remarked) that lixivious falts are alike purgative, whatever may be the fhape of their angles, whether more or lefs acute or obtufe. 134. Sir Ifaac Newton accounts for the watery acids making earthy corpufcles foluble in water, by fuppofing the acid to be a mean between earth and water, its particles greater than thofe of water, and less than thofe of earth, and ftrongly to attract both. But perhaps there is no neceffary. reafon for fuppofing the parts of the acid groffer 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 cohefion with the bodies to which they are joined? 135. The acid fpirit or falt, that mighty inftru ment in the hand of nature, refiding in the air, and diffused throughout that whole element, is difcer. nible alfo in many parts of the earth, particularly in foffils, fuch as fulphur, vitriol, and allum; it was already obferved from Homberg, that this acid is never found pure, but hath always fulphur joined with it, and is claffed by the difference of its fulphurs, whether mineral, vegetable, or animal. 136. Salts are vulgarly reckoned the most active of chemical principles. But Homberg derives all their their activity from the fulphurs joined with them. From which alfo, as hath been faid, he derives all their kinds and differences (g). Salt, water, oil, and earth feem to be originally the fame in all vegetables. All the difference, according to the chemifts, arifeth from a spirit refiding in the oil, called the Rector or Archæus. This is otherwise called by chemifts, ens primum, or the native fpirit, whereon depend, and wherein are contained, the peculiar flavour and odour, the specific qualities and virtues of the plant. 137. Thefe native fpirits or vegetable fouls are all breathed or exhaled into the air, which feems the receptacle as well as fource of all fublunary forms, the great mass or chaos which imparts and receives them. The air, or atmosphere, that furrounds 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 perfpires, corrupts, or exhales, impregnates the air; which, being acted upon by the folar fire, produceth within itself all forts of chemical operations, difpenfing again thofe falts and fpirits in new generations, which it had received from putrefactions. 138. The perpetual ofcillations of this elastic and reftlefs element operate without ceafing on all things that have life, whether animal or vegetable, keeping their fibres, veffels, and fluids in a motion always changing; as heat, cold, moisture, dryness, and other causes alter the elafticity 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 ruft in the air, and bodies of all forts are diffolved or corrupted, (g) 129. which which fheweth an acid to abound and diffuse itself throughout the air. 139. By this fame air fire is kindled, the lamp of life preferved, refpiration, digeftion, nutrition, the pulfe of the heart and motion of all the muf cles feem to be performed. Air therefore is a ge neral agent, not only exerting its own, but calling forth the qualities or powers of all other bodies, by a divifion, comminution, and agitation of their particles, caufing them to fly off and become volatile and active. 140. Nothing ferments, vegetates, or putrefies without air, which operates with all the virtues of the bodies included in it; that is, of all nature; there being no drug, falutary or poisonous, whofe virtues are not breathed into the air. The air there fore is an active mafs of numberlefs different prin ciples, the general fource of corruption and generation; on one hand dividing, abrading, and carrying off the particles of bodies, that is, corrupting or diffolving them; on the other, producing new ones into being; deftroying and bestowing forms without intermiffion. 141. The feeds of things feem to lye latent in the air, ready to appear and produce their kind, whenever they light on a proper matrix. The extremely fmall feeds of fern, moffes, mushrooms, and fome other plants are concealed and wafted about in the air, every part whereof feems replete with feeds of one kind or other. The whole atmosphere seems alive. There is every where acid to corrode, and feed to engender. Iron will ruft, and mold will grow in all places. Virgin earth be comes fertile, crops of new plants ever and anon fhew themselves; all which demonftrates the air to be a common feminary and receptable of all vivifying principles. I 142. Air |