306 Researches upon the Heat developed in Combustion. 
it is not because I suppose that the heat developed in com-~ 
bustion is more intense at the primitive source in a large 
than ina small fires but as a small fire is always surrounded 
by bodies relatively very cold, such as the bars of the grate, &e. 
the products of the combustion (which are always at the 
instant of their formation at the same temperature) are so 
rapidly cooled when the fire is small, that the temperature 
which we may find in such a fire is necessarily lower than 
that which we find in the midst of a larger fire, where a 
greater quantity of the same kind of combustible is em- 
ploved. 
When a large charcoal fire is well lighted up ina close 
stove, constructed with bricks or fire stones, all the inte- 
rior surfaces become excessively hot, and the heat accumu- 
lates and becomes very intense throughout the whole in- 
terior of the stove, so that iron and eve n stones are melted 
in it, and flow like liquids: but when the fire place is small, ~ 
itis with difficulty that it can be heated so much as to make 
the sides red hot; and if the fire-place be very small, a char- 
coal fire cannot be kept up at all, even with continual blow- 
ing. We may truly say that such a fire. dies of cold, an-ex- 
pression which with as much force as justice describes the 
event as it really happens. 
But if it be the cold communicated by the surrounding 
bodies which hinders a very small charcoal fire from burn- 
ing, could we not make it burn by guarding it in a proper 
manner agajnst the cold ? 
This is an experiment which I tried six years ago with 
the greatest success, and which ended in my causing to be 
made small portable cooking stoves now in general use in 
Paris, and elsewhere for aught I know. 
By surrounding the body of the stove with two strata of 
inclosed air, the cooling of the fire-place and the char- 
coal it contains is hindered: and in this way the charcoal 
burns perfectly well, and the fire is so well kept up that it 
obeys a small register, which regulates the quantity of air 
admitted into the body of the stove. 
Some judgement may be formed of the advantages which 
ought to result from the use of these small portable fur~ 
naces in cooking, &c. arising from the saving of time and 
combustibles, when we are informed that the combustion 
may be regulated without, any difficulty, so as to consume 
the charge of charcoal in 20 minutes with a brisk heat, or 
so as to keep up a moderate fire for three hours. 
With these portable cooking stoves it is indispensably, 
necessary 
