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be melted in drops at the bottom of the veffel,and converted into an Oxyd of Iron.

The above are only a few of a number ofbeautiful experiments which have been devifed,to {hew the rapidity with which bodies burn inoxygen gas, and the products of fuch com-buftion.

The procefs of combultion, which is one ofthe moft linking and moll familiar of all thenatural phenomena, has long engaged the ut-moft attention of philofophers. It is not ourintention, in a work like the prefent, whichchiefly aims at colletSing and recording fadtsand familiar proceffes, to give any hiltory of thetheories that have been advanced on this curiousand difficult fubjedt. It will be fufficient toobferve that there have been at lead three hypo-thefes made to account for combultion, togetherwith feveral modifications of each. The firftin order of time is the Phlogifiic theory, whichwas brought to a very ingenious fyllem byStahl, who is generally looked upon as its au-thor. This able philofopher fuppofes that allinflammable bodies (or fuch as burn withemiffion of light and heat) contain a portion ofan intangible, imponderable principle, calledphlogilton, to which they owe their inflamma-bility with all its attendant phenomena. Whilfta body is burning, it parts with its phlogilton,which paffes into combination with the ambientair, and it is thus reduced for the moll part intoan alh, or (if a metal) into a calx, which differsfrom the original fubltance only in being de-prived of phlogilton. Therefore (to take ametal as an example) in order to reduce thecal .v to the metallic Hate, it is neceffary tounite it with fome inflammable fubltance, fuchas charcoal, which reltores its phlogilton, andbrings it back to the metallic or reguline Hate.

But this ingenious hypothefis was made beforethe difcovery of oxygen, and before the precifeagency of air in maintaining combultion wasunderltood, and therefore the feveral modifica-tions made to accommodate it to all the thenknown chemical fa6ts, were all effentiallydefective.

ine ancovery ot oxygen oy ux. rrieitfollowed at no great length of time, which ;rffe to the moll admirable and beautifulearches of Lavoifier, on the fubjedt of cu 'on, in which this excellent philofophermonttrated that in all cafes of combultion,^. mrna fiie fubltance united with oxygen,p ucec either an acid, or an oxyd, or w;or a mixture 0 f thefe three, and the weigfthe product above that of tire Ample comb,

ble was exactly equal to the quantity of oxygenwhich had difappeared. In this refpect there-fore the fyltem fo finely brought out by Lavoifierwas not fo much an improvement of Stahl’s, asan effential addition to it and all other previoustheories,by accounting for the increafe of weightof the product of combultion over that of thecombuftible. But combufwn implies the difen-gagement of light and heat, which was Hill tobe explained, and this was done by Lavoifier,to the utter exclufion of phlogilton (the exilt-ence of which was at all times very problemati-cal) by fuppofing oxygen gas to be a compoundof oxygen with heat and light, and thereforewhilft a body burns (according to Lavoifier) itabforbs oxygen from the air, feparating it fromthe heat and light with which it was united,and which then appear in the fenfible form offire. This fyltem therefore allows of no otherdifference between combultion and flow oxyge-nation, than that in the former cafe, the pro-cefs going rapidly, tire heat and light feparatedfrom the oxygen gas appear in the form ofvifible flame, and in the latter they efcape flowlyand imperceptibly to the fenfes.

From the way in which Lavoifier expreffeshimfelf however, it might be fuppofed, that heconceived that the only portion of caloric whichcould be fet free during combultion, was thatwhich is effential to the gafeous form, or thatwhich makes the foie difference between a folidbody and the fame body gaflified, analogous tothe difference in this refpedt between fleam andfluid water. Hence it would follow that no oxy-gen in folid or liquid combination could main-tain combultion, a pofition which is inltantlyrefuted by the well-known power of the folid.oxygen of nitre and oxymuriat of potafh to in-flame charcoal, or the liquid oxygen of nitricacid to kindle effential oils.

If therefore oxygen is the fource of the heatdifengaged during combultion (which is ex-tremely probable) it mull be allowed in feveralinllances to carry the greater part of its heatwith it into various combinations, fo that theoxygen of nitric acid which can fupport com-bultion, mult be allowed to be different fromthat of water (for example) which cannot:and nitric acid therefore mult be called a com-pound of azot, and oxygen with its caloric ; andwater a compound of hydrogen and oxygenwithout its caloric. This diftindtion has been,well pointed out by Brugnatelli, “ who termsthe former date thermoxygen , and the latterfimply oxygen.

It is a preemptive argument too, that the

* Joum. de Phyf. tom. 53.