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By fuel we mean whatever receives and retains fire, and 

 is consumed thereby. The only fuel in nature is oil or 

 sulphur, and bodies are only rue!, as containing oil. 

 Hence, 1. All vegetables net too moist or two dry, af- 

 ford fuel, particularly those which contain much oil, as 

 balsamic and resinous woods. 2. All vegetable and ani- 

 mal coals, being those parts which have exhaled their; 

 water and salt, and retained the oil alone inhering in the 

 earth. 3. All bituminous earth. 4. All mineral sulphur, 

 whether pure or joined with other things. 5- The fat 

 and dung of animals : and 6. Chymical oil and spirits. 



On the removal of air, this lire goes out. Yet it 

 does not immediately bear the air, but repels it, and by 

 that means forms a kind of vault, which by it weight, 

 and the pressure of the incumbent air, confines the par- 

 ticles that would otherwise escape, and applies them to 

 the combustible matter. Hence the heavier the air, the 

 fiercer the fire ; which therefore is fiercest in still, cold 

 weather. 



The fire in burning combustible matter, affords a shin- 

 ing fire or rlame, or both : and frequently too, smoke, 

 soot and ashes. Shining fire seems to be elementary 

 fire, so strongly attracted toward the particles of the 

 fuel, as to whirl, divide, attenuate them, and thus ren- 

 der them volatile, and just fit to be expelled. Flame 

 seems to be the most volatile part of the fuel, greatly 

 rarefied and heated red hot. Soot is a sort of coal con- 

 sisting of a thick sulpher, and an attenuated oil, with 

 earth and salt. Smoke is the earthy and watiy particles 

 of the fuel, so rarefied as to break through into the at- 

 mosphere. Ashes are the earth and salt, which the fire 

 leaves unchanged. 



Fire increases the weight of some bodies. Thus if 

 antimony be placed under a burning glass, the great- 

 est part of it will seem to evaporate in fumes, and 

 yet if it is weighed, it will be found to have gained in 

 weight. 



But beside the solar, there is a subterraneous fire. 

 The earth is only cold to the depth of forty or fifty feet. 

 Then it begins to grow warmer; and at a great depth it 

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