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436 INFLAMMABLE SUBSTANCES. Sc&. 22$. thofe which iiithefireffevv their differences by af fording demonftrated, than the phlogifton fuppofed by the great Stahl' and his followers. Mr. Fourcroy has propofed another fyf- tem after Mr. Lavoifier, which feems lefs objeaionable: he fays, that combuftible bodies are thofe, which have a ftrong attraction to unite or combine with pure or dcphlogiflicatcd air ; and that combufiion is nothing elfe but the adf of that com bination. This, affection is grounded on the following fadis : ift, That a body cannot be burnt without air : 2dly, That the purer is this air, the more rapid is the combufiion : jdly, That in combufiion, an abforption or waftG of air is always obferved; and 4thlyj That the refidiium contains often a very fenfibie quantity of that pure air, which it abforbed, and which may fometimes be extracted from it. According to this theory of combujlion, the objections again!! the exif- tence of phlogifton, which indeed cannot be demonftrated by an immediate indication to our fenfes, are intirely avoided. But theie arc fo many phenomena in mineralogy, chemiftry, and natural philofophy, which cannot be well underftood, nor properly accounted for, without admitting phlogifton as a fub- flance, to the prefence or abfence of which they arc adequately attributed, that thefhlogifiic principle cannot be exploded, with propriety, from the theoretic part of Chemiftry. See the note to the folieiving SeRion about the exijlence of Phlogifton. Long before Mcftieurs Lavoilier and Fourcroy communi cated their dodtrine of combufiion to the public, the Trealifc ot Mr. Schcele on fire was publiftied, in 1777, a t Stockholm, in which this great Chemift difclofes his new fyftem 011 fire, hat, light, and phlogifon ; _ thefe he reprefents, in fuch a ftriking manner, as being different fubftanccs, though nearly related to one another, that we fliould hardly refufe our con viction to his inductions, were they generally fupported by fafts, and more confonant to our former itieas on a fubieft fo little perceivable by our fenfes. Hec.t, according to this able Chemift, is a compound fubftance, confifiing of phlogifton and Empyreal hr. The calces of gojd, which can be reduced to 1 metallic form, by heat alone, in a retort, fttevv that phlogifton is contained in heat: bccaufe it combines with the calces to revive
