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2. On the effects of rarefaction by heat on combustion andexplosion.

The results detailed in the precedingsection are indirectly opposed to the opi-nion of M. de Grotthus, that rarefactionby heat destroys the combustibility of gas-eous mixtures. Before I made any directexperiments on this subject, I endeavouredto ascertain the degree of expansion whichcan be communicated to elastic fluids bythe strongest heat that can be applied toglass vessels. For this purpose I introducedinto a graduated curved glass tube somefusible metal. I heated the fusible metaland the portion of the tube containing theair included by it, under boiling water torsome time. I then placed the apparatus ina charcoal fire, and very gradually raisedthe temperature till the fusible metal ap-peared luminous when viewed in the shade.At this time the air had expanded so as tooccupy 2.25 parts in the tube, it being 1 atthe temperature of boiling water. Anotherexperiment was made in a thicker glasstube, and the heat was raised until the tubebegan to run together ; but though this heat