Essays; Political, Economical, and Philosophical Part 33

At a quarter before 8 o'clock, the proper quant.i.ty of leaven was mixed with the meal, and 48 quarts, or 86 lbs. 20 loths, of water being added, at 30 minutes past 11 o'clock, this ma.s.s was prepared for kneading, by adding to it 52 quarts, or 93 lbs.

27 loths, of water.

Four minutes after 1 o'clock, 2 1/2 lbs. of salt were added.

The dough being kneaded at 15 minutes after two o'clock, 188 loaves of bread were made, which were put into the oven 5 minutes before 3 o'clock, and taken out again at the end of one hour, when 25 of them were weighed, and found to weigh, one with the other, 2 lbs. 5 1/2 loths.

The water used in making this batch of bread was 180 lbs. 15 loths.

Fourth Heating of the Oven.

This was begun 15 minutes after 12 o'clock, with 40 lbs. of wood, and 50 lbs. more being added at 30 minutes after 1 o'clock, the total quant.i.ty used was 90 lbs.

FIFTH BATCH.

At 1/4 before 12 o'clock, the proper quant.i.ty of leaven was mixed with the meal, and 52 quarts, or 93 lbs. 27 loths, of water put into it.--This ma.s.s was prepared for kneading at 15 minutes after 4 o'clock, by the addition of 48 quarts, or 86 lbs. 20 loths, of water. The kneading of the dough was begun at 5 o'clock, and at 30 minutes after 5 it was made into loaves, 2 1/2 lbs. of salt having been previously added.

186 loaves being made out of this dough, they were put into the oven at 10 minutes before 7 o'clock, and taken out again at the end of one hour, when 25 loaves were weighed, and found to weigh 55 lbs. 18 loths.--The quant.i.ty of water used in making the dough for this batch of bread was 180 lbs. 15 loths.

Fifth Heating of the Oven

The oven was begun to be heated the fifth time at 15 minutes after four o'clock, with 40 lbs. of wood, and 40 lbs. more were added at 6 o'clock; so that in this heating no more than 80 lbs. of wood were consumed.

SIXTH BATCH.

The meal was mixed with leaven at 30 minutes after 3 o'clock; for which purpose 32 quarts, or 57 lbs. 24 loths, of water were used at 15 minutes after 7 o'clock. This ma.s.s was prepared for kneading, by the addition of 44 quarts, or 79 lbs.

13 loths, of water, and a proportion of salt; at 19 minutes after 9 o'clock the dough was kneaded the first, and at 1/4 before 10 the second time; and in the course of half an hour 160 loaves were made out of it, which were put into the oven at 10 minutes before 11 o'clock, and taken out again at 8 minutes before 12 o'clock at midnight.

The water used in making the dough for this batch of bread was 137 lbs. 5 loths.

Sixth Heating of the Oven.

At 1/4 after 8 o'clock, the sixth and last fire was made with 40 lbs. of wood; to which, at 15 minutes before 10 o'clock at night, 34 1/2 lbs. more were added; so that in the last heating 74 1/2 lbs. of wood only were consumed.

GENERAL RESULTS of these EXPERIMENTS.

The ingredients employed in making the bread in these six experiments were as follows: viz.

lbs. loths.

Of rye meal, -- -- 1736 0 Of water,-- -- -- 1061 5 Of salt, -- -- -- 15 0 ----------- In all, 2812 5 in weight.

Of this ma.s.s 1102 loaves of bread were formed, each of which, before it was baked, weighed 2 1/2 lbs.; consequently, these 1102 loaves, before they were put into the oven, weighed 2755 lbs.: but the ingredients used in making them weighed 2812 lbs.

5 loths. Hence it appears, that the loss of weight in these six experiments, in preparing the leaven,--from evaporation, before the bread was put into the oven,--from waste, etc.--amounted to no less than 57 lbs. 5 loths.

In subsequent experiments, where less water was used, this loss appeared to be less by more than one half.

In these experiments 1061 lbs. 5 loths of water were used to 1736 lbs. of meal, which gives 61 lbs. 4 3/4 loths of water to 100 lbs. of meal. But subsequent experiments showed 56 lbs.

of water to be quite sufficient for 100 lbs. of the meal.

These 1102 loaves, when baked, weighed at a medium 2 lbs. 5 1/2 loths each; consequently, taken together, they weighed 2393 lbs.

13 loths: and as they weighed 2755 lbs. when they were put into the oven, they must have lost 361 lbs. 19 loths in being baked, which gives 10 1/2 loths, equal to 21/160 or nearly 1/8 of its original weight before it was baked, for the diminution of the weight of each loaf.

According to the standing regulations of the baking business carried on in the bakehouse of the Military Workhouse at Munich, for each 100 lbs. of rye meal which the baker receives from the store-keeper, he is obliged to deliver 139 lbs. of well-baked bread; namely, 64 loaves, each weighing 2 lbs. 5 1/2 loths.

And as in the before-mentioned six experiments, 1736 lbs. of meal were used, it is evident that 1111 loaves, instead of 1102 loaves, ought to have been produced; for 100 lbs. of meal are to 64 loaves as 1736 lbs, to 1111 loaves. Hence it appears that 9 loaves less were produced in these experiments than ought to have been produced.

There were reasons to suspect that this was so contrived by the baker, with a design to get the number of loaves he was obliged to deliver for each 100 lbs. of meal lessened;--but in this attempt he did not succeed.

Quant.i.ty of Fuel consumed in these Experiments.

Dry pine-wood.

lbs. loths.

In heating the oven first time, -- -- 366 16 second time,-- -- 134 16 third time, -- -- 100 0 fourth time,-- -- 90 0 fifth time, -- -- 80 0 sixth time, -- -- 74 16 ------------ Total, 845 16 Employed in keeping up a small fire near the mouth of the oven while the bread was putting into it, -- -- -- 34 16

Total consumption of wood in the six experiments,-- -- -- -- -- -- -- 880 lbs.

The results of these experiments show, in a striking manner, how important it is to the saving of fuel in baking bread, to keep the oven continually going, without ever letting it cool: for in the first experiment when the oven was cold, when it was begun to be heated, the quant.i.ty of wood required to heat it was 366 1/2 lbs.; but in the sixth experiment, after the oven had been well warmed in the preceding experiments, the quant.i.ty of fuel required was only 74 1/2 lbs.

As in these experiments 2393 lbs. 13 loths of bread were baked with the heat generated in the combustion of 880 lbs. of wood, this gives to each pound of bread 11 1/3 loths, or 34/96 of a pound, of wood.

In the fifth experiment, or batch, 186 loaves weighing (at 2 lbs.

5 1/2 loths each) 304 lbs. were baked, and only 80 lbs. of wood consumed, which gives but a trifle more than 1/4 of a pound of wood to each pound of bread; or 1 pound of wood to 4 pounds of bread.

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 quant.i.ty 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 quant.i.ty 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 quant.i.ty 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 quant.i.ties of absolute heat; or, in other words, to require different quant.i.ties of heat, to heat equal quant.i.ties 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 quant.i.ty 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 quant.i.ty of absolute heat as water,--as the quant.i.ty of meal in each loaf, was 1.47 lb., it appears, that this quant.i.ty would have required, (upon the above supposition,) to heat it from the temperature of 55 degrees, to that of 212 degrees; a quant.i.ty 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 quant.i.ties of heat required to heat any number of degrees, the same given quant.i.ty (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 quant.i.ty 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

To heat the rye meal, 1.47 lb in weight, .. 0.02899 -------- Total, 0.07335 lb.

To complete the computation of the quant.i.ty of fuel necessary in the process of baking bread, it remains to determine, how much heat is required, to send off in steam, from one of the loaves in question (after it has been heated to the temperature of 212 degrees), the 10 1/2 loths, equal to 21/64 of a pound of water, which each loaf is known to lose in being baked.

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