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ARTICLE IV.
OF HEAT.
HEAT, I conceive to be an elementary principle, existing as a component part of all substances, but in different proportions. Combustibles contain the largest quantities, in that state which Dr. Black, the celebrated Lecturer on Chemistry, has called a latent, or state of secret inactivity.
Combustion is the operation by which this latent principle
is excited into action; all that is contained in the body or matter consumed,
as well as all contained in the air used in the operation, is changed into
a state of activity, susceptible of being transmitted from one body to another,
until it finds rest or becomes latent again. The principles are too mysterious
for our comprehension, we can only observe the effects. We can see that
heat in the operation of combustion, appears to melt the fuel, or dissolve
it into a fluid, so thin and rare as to be imperceptible. It is dissipated
and flies away into the air, where the heat becomes latent again. The expansive
force of fluids formed by heat, is the subject under consideration; the
atmosphere is the great reservoir into which all active heat returns to
a latent state.* Let us suppose each column of the atmosphere, whose base
is equal to a square foot, contains an equal quantity of latent heat, of
water in a state of vapour, and of the permanent elastic fluids; and suppose
one of those
*It may pervade all space, which ancient philosophers held was filled with what they called ether.
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columns of air to be included in a cylinder, and compressed into half the space; then, by the Boylean law, (see article 6) it would have double elastic power, if compressed into one tenth part of the space, ten times the elastic power, if into one hundredth part of the space, one hundred times the power, &c. The aqueous vapour would be pressed into hot water, in the bottom; the latent heat would become active, heat the cylinder, escape into the surrounding air, and then become latent again. Then if the piston were suddenly drawn up, the alr could not expand to its original bulk, having lost its proportion of latent beat and water, until that proportion would be restored. That the results would be as stated has been proven.* These serve to shew that compressed air or strong elastic steam do not contain as much heat in a latent state as weaker, in proportion to their power, and that the Boylean law is an error.
If heat be applied to melt ice of the temperature of 32
degrees of Fahrenheit, 147 degrees of it find rest in
*See the American edition of the Encyclopedia.
Experiments were made to ascertain the elasticity of air, in proportion
to its density, by condensing it in a cylinder with a piston. It was found
that double density did not produce quite double elasticity, nor quadruple
density quadruple elasticity, &c. The experimenters were surprised to
find, that great compression made the cylinder hot, and filled a vial, which
they had inserted in the bottom of the cylinder, with water. From this experiment
we may safely infer, that air and steam do not contain heat in direct proportion
to their density, but rather in an inverse ratio, that is, the greater their
density the less latent heat they contain in the space they occupy; that
a vacuum contains more latent heat than a plenum, and that the atmospheric
air is not a permanent elastic fluid.
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the water made by melting the ice, and is necessary as a constituent part of the water to keep it in a fluid state, latent and imperceptible to the thermometer, which indicates it to be of the same temperature the ice was in. If we continue to apply heat to the water until we raise its temperature to 212 degrees, it will begin to produce elastic vapour, equal in power to the weight of the atmosphere, which it now lifts and continues to resist. In this vapour under the pressure of the atmosphere, from 800 to 1000 degrees of heat, returned into a latent state, find rest; being, under that pressure, a constituent part of vapour, and necessary to continue it in that state; the thermometer indicating the same degree of heat as of the boiling water, which is 212 degrees. This is proven by Dr. Black.*
If the weight of the atmosphere be taken off the water,
it will boil at 70 degrees of heat; but in this case, 1300 or perhaps 2000
degrees of heat in this weak vapour, find rest or become latent rising under
no pressure. The less the pressure on the surface of of boiling water, the
more heat is required to raise it all into vapour; on the contrary, the
greater the pres- sure, or the greater the elastic power of steam, the less
the heat or fuel required to raise it all into vapour. The heat cannot find
room, amongst the particles of strongly compressed steam, to become latent,
but remains active to increase the power. If we increase the pressure on
the surface of the water from 1 to 8 atmospheres, it will not boil until
the heat be increased 90 degrees above
*See his Lectures, vol.1.
See the celebrated James Watt's experiment to distill in vacuo. Black's
Lectures vol 1.
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212; that is, 302 degrees, when the power of the steam will be 120 pounds to the inch. (See the scale, art. 3). The water will then begin to boil, and the steam to rise, lifting the weight of 8 atmospheres an equal distance in equal time, which may be compared to a load on an engine. Here it appears that, after the loss of heat occasioned by its becoming latent ceases (as all that loss takes place in raising the temperature the first 212 degrees), we can, by the addition of the small quantity of fuel which will be required to increase the heat 90 degrees, gain 8 times the power, produce 8 times the effect, or carry 8 times the load an equal distance. But we will shew, in the proper place, that steam of power equal to 8 atmospheres can be applied to work an engine, to produce much more than 8 times the effect. See art. 7, where it is shewn that it produces 22.6 the effect, or perhaps 32 times.
As heat appears to melt or dissolve the fuel in combustion,
into a thin elastic fluid, with which it passes off into the air to return
to a latent state; so it appears to dissolve the water into a much thinner
fluid called elastic steam, with which it passes off into the air, there
to find rest in a latent state. The quantity of beat passing off, appears
to be in some ratio to the space into which the steam is permitted to expand
and occupy; perhaps in direct proportion, that is, double space may be capable
of receiving double quantity of heat in a latent state. One cubic inch of
water rising freely into steam in vacuo, carried with it 1300 or perhaps
2000 degrees of heat in a latent state, while the same quantity rising under
the pressure of the atmosphere, which confines the steam to a less space,
carried off but 1000
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degrees of heat in a latent state; from which we may safely infer, that as the pressure is increased from 1 to 2, and so on to 8 atmospheres, or the steam confined to a smaller space, by giving it a greater load, that the heat carried off in a latent state will be lessened from 1000 to 750, 500, 250, 125 degrees, or in some other ratio not yet ascertained.
As heat enters water, formed by melting ice, slowly, and becomes latent in the water, so it also leaves the water slowly, becoming sensible or active again as the water freezes. But on the contrarry, as the heat leaves hot water quick as lightning (comparatively speaking) when the compression is taken from off its surface, be coming latent in the form of elastic vapour, so also it leaves the vapour instantly, to enter water or other matter of a lower temperature, and the vapour is condensed, forming the same quantity of water which was used in its formation; the heat becoming active and sensible to the thermometer, which will indicate the rise of temperature in the water used to condense it: all which has been proven by Doctor Black, although not shewn in the very same point of view.* When we consider the irresistible power of steam, we may say, with propriety that we have at our command a physical agent, whose operations are quick as lightning, and powerful as thunder.
From the foregoing facts we may safely draw the following
inference, viz. That the quantity of water necessary to condense any quantity
of elastic steam, under any pressure, will be such as is just sufficient
to
*See his Lectures, vol 1.
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receive all heat from the steam, into the water, leaving
it of the temperature at which water is just ready to boil under such pressure;
therefore the colder the water, the less will be required. If the condensation
be made under no pressure, or in a vacuum, it will require a much larger
quantity of cold water, because it will not bear to be heated to 70 degrees,
the boiling heat of water in vacuo.*
*A competent knowledge of those principles, leads us directly to the discovery of a variety of curious and important improvements and inventions, which may lead on to others, viz.
1. Steam engines which will be inexhaustible in their operation. Once filled with water they will require no supply; no sediment can accumulate to cause the boilers to burn out; they will therefore last much longer.
2. Stills to suppress the watery vapour and essential oils which give the spirits a bad flavour, and to take off the spirits pure at one operation, which may be made perpetual, or without intermission.
3. Boilers for distillers and brewers, by which their largest vessels can be heated to any degree, in a much shorter time, and with less expense.
4. Inexhaustible boilers for heating apartments where fire would be dangerous, if used in the common way.
5. Furnaces and boilers may be so constructed, that all
the heat, which in common furnaces ascends the flue or chimney, may be poured
immediately into the water, to generate steam; and all the elastic fluid
generated by the consumption of the fuel, applied to aid the steam in working
the engine; lessening the weight of the engine to about one-tenth part,
and the consumption of fuel to about one-fourth part, and yet produce as
much power as the best English engines. An engine thus constructed will
be the most suitable for the great purposes of propelling boats against
the stream of the Mississippi, and carriages on turn-pike roads, &c.
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Here it appears almost impossible to form a perfect vacuum,
by condensing the steam with water, by the use of condensers to steam engines;
all their use being to take off the resistance of the atmosphere, which
can be effected in part only, and considering the very small quantity of
additional fuel required to overcome that resistance, their advantages seem
to vanish. For if the condensing water be heated to 160 degrees, then, by
the scale of experiments, (art. 3.) the power of steam left in the condenser
will be 3.75 pounds to the inch; this deducted from 15 leaves 11.25 pounds,
which is all the resistance taken off by the condenser. Again, if we supply
our boiler with this condensing water of the temperature of 160 degrees,
it will lower the temperature in the boiler perhaps 30 degrees, from 310
to 280 degrees, and by that means reduce the elastic
But the expense of the experiments necessary to bring these principles
into operation would be too great. No prudent man will risk the attempt,
until the prospects of a sufficient reward brighten. We unite in a belief,
that fate has ordained that the ingenious man shall never be rich; not considering
that it is the injustice and impolicy of most governments, that have passed
the decree. Who would get rich if the property he acquired by his industry
was to become common as soon as he gained it? or even if it was to be the
case at the end of fourteen years. What prudent man will spend his thoughts,
time, labour and money, for property no better secured to him. Ingenuity
makes none poor, but on the contrary, has made many rich, whose prudence
directed them to the pursuit of permanent property. To ingenuity we owe
all our superiority over savage nations. England has made herself more rich
and powerful than other nations, by her more liberal policy of securing
to ingenious men, the exclusive right to their inventions, so long as to
afford them an opportunity of being amply rewarded.
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power of the steam from 120 to 60 pounds, (see the scale,
article 3.) which would be losing 22.4 pounds, the average of 60 pounds,
to gain 11.25.* (See the scale article 6.)
RECAPITULATION.
I have shewn,
1st, That a great quantity of heat is expended in raising the temperature of water to a boiling degree, or 212 degrees, to produce steam of elastic power only equal to the pressure of the atmosphere, which is equal to 15 pounds to the inch surface of the water.
2dly, That the elastic power of the steam increases in a geometrical ratio, as the heat increases in an arithmetical ratio; every addition of about 30 degrees or heat in the water, doubling the elastic power of the steam; so that doubling the heat of the water increases the power of the steam about one hundred times.
3dly, That the proportional quantity of heat to be added to double the power, decreases in a rapid ratio as the heat in the water increases; that by adding 30 degrees of heat to the high temperature of 370 degrees, we gain 4363 times as much power as we gain by adding 30 degrees to the low temperature of 10 degrees.
4thly, That the heat escapes in a latent state in weak
steam, in much greater quantity in proportion to the power, than it does
in strong elastic steam; that this loss of heat in a latent state may be
in direct
*But if this supply-water be driven first into a
vessel, through which the flue of the furnace is made to pass, to heat it
to the temperature of the water of the boiler before it enters, it will
not then reduce either the heat or power of the steam.
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proportion to the space in which the steam is suffered to expand. This has been proven by John Dalton.*
1st, He placed a thermometer in the centre of a large receiver, and condensing the air by forcing more in, the thermometer rose quickly several degrees, and opening the cock to let the air escape, it sunk quickly several degrees lower than the temperature of the atmosphere. Why were these effects produced? I answer, because when the air was condensed, there was not room for the heat to remaln in the receiver in a latent state; and in its efforts to find room, it became active, ran into the thermometer, expanded the quicksilver; and caused it to rise: but if left in that state, the heat soon passed through the glass receiver, and an equilibrium being restored, the thermometer settled to its proper degree. When the cock was opened, the air escaping, left more room for latent heat than could be filled by the heat left in the receiver, therefore the heat in the thermometer left it, and the mercury contracted and fell to meet the temperature of the space inside of the receiver, but being left in that state, the equilibrium was soon restored, by the heat of the surrounding atmosphere entering through the glass receiver.
2dly, Exhausting the receiver, the thermometer fell suddenly
several degrees, because this increased the capacity of the space within
the receiver for receiving and retaining heat in a latent state, which deprived
the thermometer of its heat. But an equilibrium was soon restored, by a
supply from the surrounding atmosphere.
*See his experiments...Repertory of Arts, vol. ii.
series 2.
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These experiments clearly prove that a vacuum has a greater capacity for heat in a latent state than a plenum; and no other inference can be rationally drawn from the premises. They also clearly account for the wonderful effects produced by my new principle of confining the steam, and increasing the heat in the water, by which the elastic power of the steam, is increased; so that doubling the fuel, produces about 16 times the effect; enabling us, with small, simple, and cheap engines, to obtain power equal to the larger, more complex, and expensive ones, heretofore used, and with one-third part of the fuel. Although we cannot account philosophically for all these operations of nature, yet we may be satisfied with a knowledge of the facts.
It appears therefore, that to begin to use steam when it has arrived to only atmospheric power, is to stop at the point where the heat begins to produce power without loss, after which every degree of heat we add, serves with effect to increase the power in a rapid ratio. The less we confine the steam, the more fuel will be necessary; and the more we confine the steam, or the heavier we load the engine, the less fuel will be required to produce the effect we wish. Every stroke of the engine will draw off nearly an equal quantity of heat, let the load be light or heavy, and we may at least safely eonclude, that the increase of fuel or heat used, will bear no proportion to the increase of load. (See art. 3,)