Essays; Political, Economical, and Philosophical Part 34

But we have just observed, that 20 lbs. of ice-cold water may be heated to the boiling point, with the heat generated in the combustion of 1 lb. of pine-wood; it appears therefore that 20 lbs.

of boiling water would require 5 1/2 times as much, or 5 1/2 lbs.

of wood to reduce it to steam.

And if 20 lbs. of boiling water require 5 1/2 lbs. of wood, 21/64 of a pound of water boiling hot will require 0.09023 of a pound of wood to reduce it to steam.

If now, to this quant.i.ty of fuel,-- -- 0.09023 lb.

we add that necessary for heating the loaf to the temperature of boiling water, as above determined, -- -- -- 0.07335 lb.

-------- this gives the total quant.i.ty of fuel necessary for baking one of these loaves of bread,-- -- -- -- -- -- -- -- 0.16353 lb.

Now as these loaves, when baked into bread, weighed 2 lbs. 5 1/2 loths = 2 11/64 lbs. each and required, in being baked, the consumption of 0.16353 of a pound of wood, this gives for the expence of fuel in baking bread 0.07532 of a pound of pine-wood to each pound of rye bread; which is about 13 1/4 lbs. of bread to each pound of wood.

But we have seen, from the results of the before-mentioned experiments, that when the bread was baked under circ.u.mstances the most favourable to the economy of fuel, no less than 80 lbs.

of pine-wood were employed in heating the oven to bake 304 lbs.

of bread, which gives less than 4 lbs. of bread to each pound of wood; consequently, TWO THIRDS at least of the heat generated in the combustion of the fuel must, in that case, have been lost; and in all the other experiments the loss of heat appears to have been still much greater.

A considerable loss of heat in baking will always be inevitable; but it seems probable, that this loss might, with proper attention to the construction of the oven, and to the management of the fire, be reduced at least to one half the quant.i.ty generated from the fuel in its combustion. In the manner in which the baking business is now generally carried on, much more than three quarters of the heat generated, or which might be generated from the fuel consumed, is lost.