2 1 o Observations on

stances; and we do not know of any thingthat can combine with it so readily as air yand therefore we find that nothing canbum but in contact with air, and withchange of air.

When, indeed, phlogiston is set loose inthe putrefactive process, air is not absolutelynecessary. For, in that case, it may becommunicated to water, and probably toother substances fluid or solid. It does not,therefore, certainly follow, that there canbe no combustion without air, though itbe probable; because phlogiston may beable to escape without the help of air inone way, though not in another. Thesolution of the phenomena of subterraneousfires would certainly, however, be mucheasier on the supposition of their supplyingtheir own pabulum, by means of dephlogisti-cated air, contained in substances exposedto their heat. I therefore desired Mr.Landriani, who, being in Italy, had a goodopportunity of making inquiries on thethe subject, to inform me whether any ofthose substances and particularly manganese,

be