As each loaf weighed 2 lbs. 16 loths when it was put into the oven, and only 2 lbs. 5 1/2 loths when it came out of it, the loss of weight each loaf sustained in being baked was 10 1/2 loths, as has already been observed. Now this loss of weight could only arise from the evaporation of the superabundant water existing in the dough; and as it is known how much heat, and consequently HOW MUCH FUEL is required to reduce any given quantity of water, at any given temperature, to steam, it is possible, from these data, to determine how much fuel would be required to bake any given quantity of bread, upon the supposition that NO PART OF THE HEAT GENERATED IN THE COMBUSTION OF THE FUEL WAS LOST, either in heating the apparatus, or in any other way; but that the whole of it was employed in baking the bread, and in that process alone. And though these computations will not show how the heat which is lost might be saved, yet, as they ascertain what the amount of this loss really is in any given case, they enable us to determine, with a considerable degree of precision, not only the relative merit of different arrangements for economizing fuel in the process of baking, but they show also, at the sane time, the precise distance of each from that point of perfection, where any farther improvements would be impossible: And on that account, these computations are certainly interesting.
In computing how much heat is NECESSARY to bake any given quantity of bread, it will tend much to simplify the investigation, if we consider the loaf as being first heated to the temperature of boiling water, and then baked in consequence of its redundant water being sent off from it in steam.
But as the dough is composed of two different substances, viz. rye meal and water, and as these substances have been found by experiment to contain different quantities of absolute heat; or, in other words, to require different quantities of heat, to heat equal quantities or weights of them to any given temperature, or any given number of degrees, it will be necessary to determine how much of each of the ingredients is employed in forming any given quantity of dough.
Now, in the foregoing experiments, as 1102 loaves of bread were formed of 1736 lbs. of rye meal, it appears, that there must have been 1.47 lb. of the meal in each loaf; and as these loaves weighed 2 1/2 lbs. each when they were put into the oven, each of them must, in a state of dough, have been composed of 1.47 lb. of rye meal, and 1.03 lb. of water.
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 2 1/2 lbs., 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