Supposing these loaves to have been at the temperature of 55 degrees of Fahrenheit's Thermometer when they were put into the oven, the heat necessary to heat one of them to the temperature of 212 degrees, or the point of boiling water, may be thus computed.

By an experiment, of which I intend hereafter to give an account to the Public, I found, that 20 lbs. of ice-cold water might be made to boil, with the heat generated in the combustion of 1 lb. of dry pine- wood, such as was used in baking the bread in the six experiments before mentioned. Now, if 20 lbs. of water may be heated 180 degrees, (namely from 32 to 212 degrees,) by the heat generated in the combustion of 1 lb. of wood, 1.03 lb. of water may be heated 157 degrees, (from 55 degrees, or temperate, to 212 degrees,) with 0.4436 of a pound of the wood.

Suppose now that rye meal contained the same quantity of absolute heat as water, -- as the quantity of meal in each loaf, was 1.47 lb., it appears, that this quantity would have required, (upon the above supposition,) to heat it from the temperature of 55 degrees, to that of 212 degrees; a quantity of heat equal to that which would be generated in the combustion of 0.06405 of a pound of the wood in question.

But it appears, by the result of experiments published by Dr. Crawford, that the quantities of heat required to heat any number of degrees, the same given quantity (in weight) of water and of wheat, (and it is presumed, that the specific or absolute heat of rye cannot be very different from that of wheat,) are to each other, as 2.9 to 1, -- water requiring more heat to it, than the grain in that proportion: Consequently, the quantity of wood required to heat from 55 to 212 degrees, the 1.47 lb. of rye meal which entered into the composition of each loaf, instead of being .06405 of a pound, as above determined, upon the false supposition that the specific heat of water and that of rye were the same, would, in fact, amount to no more than 0.02899; for 2.9 (the specific heat of water) is to 1 (the specific heat of rye), as 0.06405 is to 0.02899.

Hence it appears, that the wood required as fuel to heat (from the temperature of 55 degrees to that of 212 degrees) a loaf of rye bread (in the state of dough), weighing 2½lbs., would be as follows, namely:

Of pine-wood,
To heat 1.03 lb. of water, which
enters into the composition of the dough, .. 0.04436
To
heat the rye meal, 1.47 lb in weight, .. 0.02899
--------
Total, 0.07335 lb.

Now it appears, from the result of Mr. Watt's ingenious experiments on the quantity of latent heat in steam, that the quantity of heat necessary to change any given quantity of water already boiling hot to steam, is about five times and a half greater than would be sufficient to heat the same quantity of water, from the temperature of freezing, to that of boiling water.

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 5½times as much, or 5½lbs. of wood to reduce it to steam.

And if 20 lbs. of boiling water require 5½lbs. 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 quantity 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 quantity of fuel
necessary for baking one of these loaves
of bread, -- -- -- -- -- -- -- --
0.16353 lb.

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