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and combustion of solid charcoal ; but toproduce this deposition from gaseous sub-stances demands a high temperature. Phos-phorus, which rises in vapour at commontemperatures, and the vapour of which com-bines with oxygen at those temperatures, asI have mentioned before, is always luminous,for each particle of acid formed must, thereis every reason to believe, be white hot;but so few of these particles exist in a givenspace that they scarcely raise the tempera-ture of a solid body exposed to them,though, as in the rapid combustion of phos-phorus, where immense numbers are exist-ing in a small space, they produce a most,intense heat.

In ali cases the quantity of heat com-municated by combustion, will be in pro-portion to the quantity of burning mattercoming in contact with the body to beheated. Thus, the blow-pipe and currentsof air operate. In the atmosphere, the ef-fect is impeded by the mixture of azote,though still it is very great: with pure oxy-gene compression produces an immense ef-fect, and with currents of oxygene and hy-drogene, there is every reason to believe,that solid matters are made to attain the