352 Phcnonienn of Comhiiflion.—Campofition tf fFaier. 



and that when they combine \\\i\\ oxygen, as above explained, the produ£ls arc wfttcr and 

 hydro- carbonate gaz. 



If I did not ule the term demonjlration in a more ftrif) and prccifc fenfe than Is ufual, 

 except in mathematics, I would venture to affirm that this theory is almoft dcmondrated 

 by the agency of fire and carbon on black oxide of mangancfe. If colourlefs vitrifiable 

 matter, and that oxide be melted together, by means of the white part of the flame of a 

 candle, purple-coloured glafs will be produced ; for then the hydrogen of this part of the 

 flame carries ofl^ little or none of the oxygen from the oxide: but if thcfe fubfl-ances be 

 melted together by the Hue part of the flame, colourlefs glafs will be produced ; for then 

 the carbon of this part of the flame carries ofl" oxygen from the black oxide, and produces 

 white oxide. By combining oxygen anew with colourlefs glafs, containing manganefc, it 

 will become purple ; and this is efloifled by melting fuch colourlefs glafo with a little nitrate 

 of pot-a(h, or by melting it in open veflels by the yellow flame of a candle. By fcparat- 

 ing oxygen from glafs rendered purple by manganefe, colourlefs glafs is produced ; anj 

 this is efl^efled by melting fuch coloured glafs with a little carbon, or by the blue flame 

 of a candle. I have not thought it necefl'ary to diftJnguifli between the indigo and violet 

 rays ; or to notice tlie extremely thin film of violet flame, which an attentive obferver may 

 perceive furrounding the inferior part of the white, extending as high but fcarcely higher 

 than the wick ; becaufe the explanation is perfcifHy obvious from the preceding diilinclion 

 of the two kinds of gazes an"orded by the candle. If I have explained more fatisfa£lorily 

 than former members of this focicty the above phenomena of combuflion, I owe this ad- 

 vantage to fome experiments of combulHon of inflammable gazes which I have "..ade for 

 fome years pad, in my chemical lectures ; by which the colours are fliewn to be very dif- , 

 ferent, and correfpond to the above theory. I apprehend the theory of an ingenious 

 member of this fociety cannot explain adequately the phenomena, and does not appear fup- 

 ported by any facts : for there is no evidence that the white flame is not equally the efFcCl 

 of immediate decompofitlon as well as the blue ; or that the blue becomes white flame by 

 ignition ; and I prefume that the experiments which I have mentioned fliew thjt thefe dif- 

 ferences depend upon difl^erent decompounding fubftances contained in the candle. 



With regard to the evidence aflxsrded by the foregoing experiments concerning the com- 

 pofition of water and of hydrogen and oxygen gaz. Thefe fubfl:ances arc now accounted 

 for in two ways only ; namely, I. By faying that thefe two gazes confift of water and im- 

 ponderable matter ; and that during combuftion the water is precipitated. 2. By faying 

 that the two gazes confift of a peculiar bafis, one of which is named oxygen and the other 

 is hydrogen, each of which is rendered into the gaz ftatc by uniting to caloric, and perhaps 

 alfo to light ; and that during combuftion thefe bafes unite with one another, thus com- 

 pounding water and difcharging caloric and light. If complete demonftration could be 

 given, there would not be two opinions ; for its proofs, if undcrdood, command univerfal 

 aflent: but the cafe being othcrwife, that opinion muft be adopted on the fide of which the 

 evidence preponderates according to the laws of reafoning in pl.yfical fcience. Now with 

 repard to the former of thefe opinions, I can perceive but two f.ifts in fupport of it. The 

 firft of thefe is fuppofed to afford a fort of fynthetical proof: it is the inftance of water 

 being required to obtain, by fire, the whole of the carbonic acid from carbonate of baryt. 

 Here the fact, if admitted, is true only of carbonic acid ; but even in this cafe it has not 



been 



