Lavoisier’s theory or combustiox.

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perties become totally altered. The principal change it suffersis that of being no longer capable of combustion.

If either of these phenomena, namely, the emission of heatand light, and the waste of substance, be wanting, we do notsay that a body is undergoing combustion, or that it is burning.

It follows therefore that every theory of combustion ought toexplain the following facts:

1. Why a burning body is consumed, and its individuality de-stroyed.

2. Why, during the progress of this alteration, heat and lightare emitted.

For the elucidation of these objects Lavoisier's theory has laiddown the following laws:

1. Combustion cannot take place without the presence of ox-igen, and is more rapid in proportion to the quantity of thisagent in contact with the inflamed body.

2. In every act of combustion the oxigen present is consumed

3. The weight of the products of every body after combustioncorresponds with the weight of the body before combustion plusthat of the oxigen consumed.

4. The oxigen absorbed by the combustible body may be re-covered from the compound formed, and the weight regainedwill be equal to the weight which disappeared during the com-bustion.

5. In every instance of combustion light and heat or fire, areliberated.

G. In a limited quantity of air, only a certain quantity of thecombustible body can be burnt.

7. The air, wherein a body has been burnt, is rendered unfitfor maintaining combustion, or supporting animal life.

Though every case of combustion requires that light and heatshould be evolved, yet this process proceeds very differently indifferent circumstances, hence the terms ignition, or glowingheat; inflammation or accension; and detonation or explosion.