158 HEAT. 



that it has entirely disappeared, except a very small 

 quantity of ashes. What has become of it 1 It has been 

 almost entirely converted into a peculiar kind of air 

 or gas, called carbonic acid gas, (dead air), which has 

 escaped, unless the experiment was conducted in proper 

 vessels for collecting it. If collected, it will be found to 

 greatly exceed in weight the charcoal first heated. 



In order that a body may burn, oxygen gas is ne- 

 cessary. And as the air we breathe is a mixture of this 

 gas and another called azote, or nitrogen, common air is 

 said to be necessary in order to enable a body to burn, or 

 in other words to undergo combustion. In every case of 

 combustion, heat and light are produced, and there is a 

 total change in the nature of the body burnt. The im- 

 mortal Lavoiser was the first who explained the phe- 

 nomenon of burning in a satisfactory manner. He sup- 

 posed that oxygen is combined with heat and light ; and 

 when therefore a body is burnt, the oxygen gas of the air 

 is decomposed, heat and light are set free, while the re- 

 mainder of the gas, or its base, combines with the body 

 burnt, and forms the product, ashes, carbonic acid gas, 

 &-c. The products will not burn, of course, because 

 they are already combined with as much oxygen as 

 possible. 



We may now explain the cause why the products of the 

 charcoal mentioned above, weigh more that the coal 

 first used. The oxygen has weight, and having combined 

 with a part of the coal, forming the dead air ; of course, 

 the products weigh more than the coal alone. 



The quantity of heat evolved during combustion is not 

 only highly important as an object of economy, but 

 interesting in a philosophical point of view. Several phi- 

 losophers have investigated the subject, and no one with 

 more success than our countryman, Count Rumford. He 

 found how many pounds of ice were melted by the burn- 

 ing of one pound of the body tried. The following table 

 shows some of his results. 



Ibs. Ibs. 



Olive Oil 93,07 Tallow 111,53 



Rape-sr-ed Oil 124,09 Alcohol 07,47 



Wax (Bees') 120,24 



The following table exhibits the results of a set of simi- 



