PRODUCTION OF HEAT. 19 



matter must be used in the course of a year, and, for reasons to be exam- 

 ined in detail presently, three quarters of a ton of water. But this is a 

 very different conclusion to the notion of the ancient physicians, that an 

 animal during its life is exempt from participating in external changes, 

 and is an enduring monument of the power possessed by the VITAL FORCE 

 of resisting all physical influences. 



But carbon by uniting with oxygen can not turn into carbonic acid, 

 nor can hydrogen turn into water, nor nitrogen into ammonia, without 

 heat being produced. The very meaning we attach to the term indicates 

 that every process of burning is attended with the liberation of heat. 



In domestic economy, we protect ourselves from the cold weather of 

 winter, or attain any high temperature we want by the oxidation of some 

 of the forms of carbon, such as wood or coal, in fire-places or stoves. 

 "We know that for the production of a given quantity of heat a given 

 weight of combustible matter and of air is required, and that by employ- 

 ing various mechanical contrivances for increasing the draught we can ac- 

 celerate* the burning. 



Moreover, if in our laboratories we require the very highest tempera- 

 ture that can be artificially obtained, we resort to the burning of hydro- 

 gen. There are instruments, such as the compound blow-pipe, construct- 

 ed on this principle. In the flame which arises in this combustion the 

 most refractory substances melt or are deflagrated. 



But it may be said that though when a substance is rapidly oxid- 

 izing it must be evolving heat, there is perhaps a slower Production of 

 kind of combination, in which the particles unite without any ^^ J^ re " 

 disturbance of temperature. What proof could be offered, for decay, 

 example, that a mouldering leaf is disengaging heat ? 



In answer to this it is not necessary to bring forward refined or direct 

 experiments. Every leaf when it moulders is literally burning away. 

 The extrication of warmth begins even when it is ready to fall. What 

 does the farmer expect in making his hay, if he puts the grass up in too 

 moist a state, or in too large a mass ? The temperature does not stop at 

 the stage of bituminous fermentation, but the stack most probably takes 

 fire. Of course what is going on in the whole mass is going on in each 

 separate leaf, undistinguishable, it is true, in the latter case, because the 

 heat of a single decaying leaf, taken alone, may be carried off by the cold 

 surrounding air, or by the contact of good conducting bodies, and so be 

 lost to examination. 



From agricultural operations we may also learn that what holds good 

 for vegetable bodies is true for animal substances. Heaps of manure or 

 of offal of any kind, if due access of air be given, exhibit the extrication 

 of carbonic acid, steam, and ammonia, and the temperature promptly rises. 

 The gardener avails himself of this fact. He uses the heat, as it is slowly 



