Specific heat

“ We need not consider the formula that we have just given as applicable to very great changes in the volume of gases. We have regarded the elevation of temperature as being in inverse ratio to the specific heat; which tacitly supposes the specific heat to be constant at all temperatures. Great changes of volume lead to great changes of temperature in the gas, and nothing proves the constancy of specific heat at different temperatures, especially at temperatures widely separated. ”

“ The capacity of a body for heat is called its specific heat. With but few exceptions the specific heats of liquids are much greater than those of solids or gases. It requires ten times the quantity of heat to raise a pound of water one degree that it does a pound of iron. Ice has the greatest specific heat of any of the solids, except paraffin and wood.
When a solid is melted or a liquid vaporized a large amount of heat becomes latent, insensible to the touch; it disappears as heat. ”

“ If, for a moment, we suppose the specific heat of air to be constant, in spite of the changes of volume and temperature, the temperature will increase in arithmetical progression for reduction of volume in geometrical progression. ”

“ That is owing to the different specific heat of ice and water. The capacity of water for caloric being greater than that of ice, more heat is required to raise its temperature, and therefore the thermometer rises slower in the water than in the ice.
EMILY.
True; you said that a solid body always increased its capacity for heat by becoming fluid ”

“ If, in place of compressing the air, we allow it to expand to two litres, four litres, eight litres, etc., it will be necessary to supply equal quantities of heat to maintain the temperature always at the same degree. ”

“ Let us suppose now that, instead of heating one degree the air subjected to a constant pressure and able to dilate freely, we inclose it within an invariable space, and that in this condition we cause it to rise one degree in temperature. The air thus heated one degree will differ from the air compressed only by its greater volume. So then the quantity of heat that the air would set free by a reduction of volume of is equal to that which would be required to raise it one degree Centigrade under constant volume. ”

“ Under favorable conditions—that is, when the differences of temperature and moisture and the supply of warm, moist air at the surface are great—this action becomes very intense, and this intensity is still further increased by the fact that as the air rises its moisture is condensed, the latent heat thus liberated adding to the energy of the rising column of air. ”

“ The gentlest summer breezes and the fiercest blasts of winter are produced by the unequal heating of air. We have seen that the air nearest to a stove or hot object becomes hotter than the adjacent air, that it tends to expand and is replaced and pushed upward and outward by colder, heavier air falling downward. We have learned also that the moving liquid or gas carries with it heat which it gradually gives out to surrounding bodies.
When a liquid or a gas moves away from a hot object, carrying heat with it, the process is called convection. ”

“ Arrived in the cloud-region, this vapour, being condensed, liberates the latent heat which it borrowed from the air and water below; which heat, being now set free and made sensible, raises the temperature of the surrounding air, causing it to expand and ascend still higher ”

“ When the ice is all melted potential energy is no longer stored, but is manifested in the sensible heating of water, the degree of which is measurable by the thermometer, until it reaches the boiling point, where it is again arrested. All of the surplus heat above that temperature is consumed in rending the liquid water into moisture globules that float away into the air, each one of them charged with a store of potential energy. Let us follow this vapor spherule as it floats into the upper regions of the atmosphere. ”

“ Rise of temperature, expansion, liquefaction, evaporation. The first indication of the presence of heat is discovered by an elevation in temperature. Though man is not a reliable thermometer, he would be able, ordinarily, even if blind, to chronicle the progress of the sun, from horizon to horizon, by the increasing and decreasing warmth. The little thermometer placed beneath the tongue of the invalid gives reliable report of the combustion going on within his system. We see a thousand illustrations of the expansive effects of heat, many of which are familiar to all. ”

“ Vast ridges and crests of incandescent vapour are upheaved by the action of internal heat, which exceeds in intensity the temperature at which the most refractory of terrestrial substances can be volatilised ”

“ That this heat is furnished by the air, he proves, by finding, that that which we inspire contains more heat than that which we expire, or than the aqueous humor which we expire along with it, in a very considerable proportion; so that if the heat contained in the pure air did not become latent in the blood, it would raise its temperature higher than that of red-hot iron. ”

“ Nevertheless, they are held together by a powerful force. Thus, the heat used in converting one pound of water at 212° F to a vapor at 212° F would raise 967 pounds of water one degree in temperature. Measured thus, in terms of heat units, great power is required to overcome molecular attraction. ”

“ Another principle of heat is Convection, by which water, air, and gases are warmed. This is, literally, the process of conveying heat from one portion of a fluid body to another by currents resulting from changes of temperature. It is secured by bringing one portion of a liquid or gas into contact with a heated surface, whereby it becomes lighter and expanded in volume. In consequence, the cooler and heavier particles above pressing downward, the lighter ones rise upward, when the former, being heated, rise in their turn, and give place to others again descending from above. ”

“ The caloric fluid was considered intangible, since even the most careful experiments in adding or subtracting heat by nondestructive heating or cooling of a substance failed to produce any changes in its weight.
Heat is energy We know now that heat is not a fluid, nor a substance at all, but is really one of the several forms of energy. ”

“ For example, in mixing five pounds of water at a temperature of 212° Fahrenheit, and five pounds of ice, seven hundred and fifteen units of heat disappear in melting the ice, and the aggregate temperature of the mass is proportionally lower than that of the substances united. ”

“ Since the capacity of water for heat is very great, if the mass of it in a circulation-apparatus be very considerable, and the circulation be accelerated by proper arrangements, as by cooling the descending tube exterior to the stove-room, we may easily obtain by such means a moderately high and uniform temperature, provided the heat generated in the fire-place be tolerably regular. ”

“ Every substance radiates its heat, and receives in return a portion of that emitted from surrounding bodies. If two bodies of unequal temperature be placed near each other, the warmer of the two will radiate a portion of its heat to the colder, and will receive some of the heat of the latter in return; but as the warmer body will emit more heat than it will receive, the result will be, that after a time, the length of which will depend on the nature of the bodies, both will acquire the same temperature. ”

“ Some of the methods of exploring these depths of cold are treated in the chapter on liquid air already referred to. Our interest here centres in the other extreme of temperature, where the heat vibrations are inconceivably rapid; where nearly all substances known to man become liquids and gases; where, in short, if the experimenter could go high enough, he could reach the awful degree of heat of the burning sun itself, estimated at over 10,000 degrees. ”

“ That portion of the heat which results in an increase in temperature of the body is called "sensible heat," inasmuch as such a gain in heat is apparent to the physical senses of the observer. If heat were supplied to the body at a uniform rate, the temperature would rise continuously, and if the temperature were plotted against time, a smooth rising curve would result. Or, if sensible heat were abstracted from the body at a uniform rate, a time-temperature curve would again be a smooth falling curve. Such a curve is called a "cooling curve." ”

“ Since solid bodies are susceptible of little change of temperature through changes of volume, and since the condition of the most effective employment of heat for the development of motive power is precisely that all change of temperature should be due to a change of volume, solid bodies appear but ill fitted to realize this power. ”

“ Through the science of thermodynamics, heat has a place in many of the industrial processes that bring us the conveniences of modern life. But as recently as 200 years ago, the true nature of heat was not understood. In the early days of science the phenomena associated with heat were ascribed to a mystical and intangible fluid called "caloric." This fluid was believed to have the power of penetrating and expanding materials, sometimes melting or dissolving them, and converting some substances to vapor. ”

“ This equalization of temperature, moreover, takes place much more rapidly, than it would do in a solid body; hence alternations of heat and cold, as day and night, summer and winter, produce in water, inequalities of temperature much smaller than those which occur in a solid body. ”

“ Each has a maximum that we cannot exceed, whatever may be, on the one hand, the machine which is acted upon by the water, and whatever, on the other hand, the substance acted upon by the heat. The motive power of a waterfall depends on its height and on the quantity of the liquid; the motive power of heat depends also on the quantity of caloric used, and on what may be termed, on what in fact we will call, the height of its fall, [13] that is to say, the difference of temperature of the bodies between which the exchange of caloric is made. ”

“ Now, water expands very much when under the influence of heat, like all liquids; solids and gases also expand upon the application of heat.
We can easily establish these statements. A metallic ring when heated is larger than when cool. A small quantity of air in a bladder when heated will fill the bladder, and water will boil over the vessel, or expand into steam, and perhaps burst the boiler. So expansion is the tendency of what we term heat.
We make use of this quality of heat in the thermometer, by which we can measure the temperature not only of liquids or solids, but of the atmosphere. ”