Heat

a bout, or turn, in horse or foot racing. By means of heats the field is gradually reduced.

Heat and Mechanical Power

It has been found that Heat and Mechanical Power are mutually convertible; and that the relation between them is definite, 772 foot-pounds of motive power being equivalent to a unit of heat, that is, to the amount of heat requisite to raise a pound of water through one degree of Fahrenheit.

n.

  Heat, says Professor Tyndall, is a mode
      Of motion, but I know now how he's proving
  His point; but this I know—hot words bestowed
      With skill will set the human fist a-moving,
  And where it stops the stars burn free and wild.
  Crede expertum—I have seen them, child.

Gorton Swope

Heat From Gas-Lighting

In the winter of 1835, Mr. W. H. White ascertained the temperature in the City to be 3° higher than three miles south of London Bridge; and after the gas had been lighted in the City  four or five hours the temperature increased full 3°, thus making 6° difference in the three miles.

Heat and Evaporation

In a communication made to the French Academy, M. Daubrée calculates that the Evaporation of the Water on the surface of the globe employs a quantity of heat about equal to one-third of what is received from the sun; or, in other words, equal to the melting of a bed of ice nearly thirty-five feet in thickness if spread over the globe.

Latent Heat

This extraordinary principle exists in all bodies, and may be pressed out of them. The blacksmith hammers a nail until it becomes red hot, and from it he lights the match with which he kindles the fire of his forge. The iron has by this process become more dense, and percussion will not again produce incandescence until the bar has been exposed in fire to a red heat, when it absorbs heat, the particles are restored to their former state, and we can again by hammering develop both heat and light.—R. Hunt, F.R.S.

Heat of Mines

One cause of the great Heat of many of our deep Mines, which appears to have been entirely lost sight of, is the chemical action going on upon large masses of pyritic matter in their vicinity. The heat, which is so oppressive in the United Mines in Cornwall that the miners work nearly naked, and bathe in water at 80° to cool themselves, is without doubt due to the decomposition of immense quantities of the sulphurets of iron and copper known to be in this condition at a short distance from these mineral works.—R. Hunt, F.R.S.

Warming With Ice

In common language, any thing is understood to be cooled or warmed when the temperature thereof is made higher or lower, whatever may have been the temperature when the change was commenced. Thus it is said that melted iron is cooled  down to a sub-red heat, or mercury is cooled from the freezing point to zero, or far below. By the same rule, solid mercury, say 50° below zero, may, in any climate or temperature of the atmosphere, be immediately warmed and melted by being imbedded in a cake of ice.—Scientific American.

Expansion of Spirits

Spirits expand and become lighter by means of heat in a greater proportion than water, wherefore they are heaviest in winter. A cubic inch of brandy has been found by many experiments to weigh ten grains more in winter than in summer, the difference being between four drams thirty-two grains and four drams forty-two grains. Liquor-merchants take advantage of this circumstance, and make their purchases in winter rather than in summer, because they get in reality rather a larger quantity in the same bulk, buying by measure.—Notes in Various Sciences.

Repulsion By Heat

If water is poured upon an iron sieve, the wires of which are made red-hot, it will not run through; but on cooling, it will pass through rapidly. M. Boutigny, pursuing this curious inquiry, has proved that the moisture upon the skin is sufficient to protect it from disorganisation if the arm is plunged into baths of melted metal. The resistance of the surfaces is so great that little elevation of temperature is experienced. Professor Plücker has stated, that by washing the arm with ether previously to plunging it into melted metal, the sensation produced while in the molten mass is that of freezing coldness.—R. Hunt, F.R.S.

Heat Passing Through Glass

The following experiment is by Mr. Fox Talbot: Heat a poker bright-red hot, and having opened a window, apply the poker quickly very near to the outside of a pane, and the hand to the inside; a strong heat will be felt at the instant, which will cease as soon as the poker is withdrawn, and may be again renewed and made to cease as quickly as before. Now it is well known, that if a piece of glass is so much warmed as to convey the impression of heat to the hand, it will retain some part of that heat for a minute or more; but in this experiment the heat will vanish in a moment: it will not, therefore, be the heated pane of glass that we shall feel, but heat which has come through the glass in a free or radiant state.

Heat  is used locally for a number of purposes in the same manner as cold, and the choice of heat or cold in the treatment of any acute form of inflammation depends almost entirely upon the wish of the patient, who generally can tell at once which will give him the greater comfort.

In sprains of the ankle, nothing compares to a hot foot-bath prolonged for hours, the object being to decrease the pain and swelling, thereby regaining the use of the limb.

The high degree of heat which can be borne by gradually increasing the temperature of the water by the addition of small quantities of scalding water, is extraordinary, and the favorable results obtained are in direct ratio to the height of the temperature.

Between these soakings, the part should be dressed with lead and opium wash, and rubbed with ichthyol ointment or camphor liniment.

Hot-water bottles or bags are also used locally for the relief of congestion and pain.

Distinctions of Heat

Among the curious laws of modern science are those which regulate the transmission of radiant heat through transparent bodies. The heat of our fires is intercepted and detained by screens of glass, and, being so detained, warms them; while solar heat passes freely through and produces no such effect. “The more recent researches of Delaroche,” says Sir John Herschel, “however, have shown that this detention is complete only when the temperature of the source of heat is low; but that as the temperature gets higher a portion of the heat radiated acquires a power of penetrating glass, and that the quantity which does so bears continually a larger and larger proportion to the whole, as the heat of the radiant body is more intense. This discovery is very important, as it establishes a community of nature between solar and terrestrial heat; while at the same time it leads us to regard the actual temperature of the sun as far exceeding that of any earthly flame.”

Vibration of Heated Metals

Mr. Arthur Trevelyan discovered accidentally that a bar of iron, when heated and placed with one end on a solid block of lead, in cooling vibrates considerably, and produces sounds similar to those of an Æolian harp. The same effect is produced by bars of copper, zinc, brass, and bell-metal, when heated and placed on blocks of lead, tin, or pewter. The bars were four inches long, one inch and a half wide, and three-eighths of an inch thick.

The conditions essential to these experiments are, That two different metals must be employed—the one soft and possessed of moderate conducting powers, viz. lead or tin, the other hard; and it matters not whether soft metal be employed for the bar or block, provided the soft metal be cold and the hard metal heated.

That the surface of the block shall be uneven, for when rendered quite smooth the vibration does not take place; but the bar cannot be too smooth.

That no matter be interposed, else it will prevent vibration, with the exception of a burnish of gold leaf, the thickness of which cannot amount to the two-hundred-thousandth part of an inch.—Transactions of the Royal Society of Edinburgh.

Heat By Friction From Ice

When Sir Humphry Davy was studying medicine at Penzance, one of his constant associates was Mr. Tom Harvey, a druggist in the above town. They constantly experimented together; and one severe winter's day, after a discussion on the nature of heat, the young philosophers were induced to go to Larigan river, where Davy succeeded in developing heat by rubbing two pieces of ice together  so as to melt each other;[1] an experiment which he repeated with much éclat  many years after, in the zenith of his celebrity, at the Royal Institution. The pieces of ice for this experiment are fastened to the ends of two sticks, and rubbed together in air below the temperature of 32°: this Davy readily accomplished on the day of severe cold at the Larigan river; but when the experiment was repeated at the Royal Institution, it was in the vacuum of an air-pump, when the temperature of the apparatus and of the surrounding air was below 32°. It was remarked, that when the surface of the rubbing pieces was rough, only half as much heat was evolved as when it was smooth. When the pressure of the rubbing piece was increased four times, the proportion of heat evolved was increased sevenfold.


[1] Could we by mechanical pressure force water into a solid state, an immense quantity of heat would be set free.

A form of kinetic energy, due to a confused oscillatory movement of the molecules of a body. Heat is not motion, as a heated body does not change its place; it is not momentum, but it is the energy of motion. If the quantity of molecular motion is doubled the momentum of the molecules is also doubled, but the molecular mechanical energy or heat is quadrupled.

As a form of energy it is measured by thermal units. The calorie is the most important, and unfortunately the same term applies to two units, the gram-degree C. and the kilogram-degree C. (See Calorie) Calories are determined by a calorimeter, q. v.

Independent of quantity of heat a body may be hotter or colder. Thermometers are used to determine its temperature.

Heat is transmitted by conduction, a body conducting it slowly for some distance through its own substance. Bodies vary greatly in their conductivity for heat. It is also transmitted by convection of gases or liquids, when the heated molecules traveling through the mass impart their heat to other parts. Finally it is transmitted by ether waves with probably the speed of light. This mode of transmission and the phenomena of it were attributed to radiant heat. As a scientific term this is now dropped by many scientists. This practice very properly restricts the term "heat" to kinetic molecular motion.

The mechanical equivalent of heat is the number of units of work which the energy of one unit quantity of heat represents. (See Equivalents, Mechanical and Physical)

Heat By Friction

Friction as a source of Heat is well known: we rub our hands to warm them, and we grease the axles of carriage-wheels to prevent their setting fire to the wood. Count Rumford has established the extraordinary fact, that an unlimited supply of heat may be derived from friction by the same materials: he made great quantities of water boil by causing a blunt borer to rub against a mass of metal immersed in the water. Savages light their fires by rubbing two pieces of wood: the modus operandi, as practised by the Kaffirs of South Africa, is thus described by Captain Drayton:

Two dry sticks, one being of hard and the other of soft wood, were the materials used. The soft stick was laid on the ground, and held firmly down by one Kaffir, whilst another employed himself in scooping out a little hole in the centre of it with the point of his assagy: into this little hollow the end of the hard wood was placed, and held vertically. These two men sat face to face, one taking the vertical stick between the palms of his hands, and making it twist about very quickly, while the other Kaffir held the lower stick firmly in its place; the friction caused by the end of one piece of wood revolving upon the other soon made the two pieces smoke. When the Kaffir who twisted became tired, the respective duties were exchanged. These operations having continued about a couple of minutes, sparks began to appear, and when they became numerous, were gathered into some dry grass, which was then swung round at arm's length until a blaze was established; and a roaring fire was gladdening the hearts of the Kaffirs with the anticipation of a glorious feast in about ten minutes from the time that the operation was first commenced.

Origin of Heat in Our System

Professor Helmholtz, assuming that at the commencement the density of the nebulous matter was a vanishing quantity, as compared with the present density of the sun and planets, calculates how much work has been performed by the condensation; how much of this work still exists in the form of mechanical force, as attraction of the planets towards the sun, and as vis viva  of their motion; and finds by this how much of the force has been converted into heat.

The result of this calculation is, that only about the 45th part of the original mechanical force remains as such, and that the remainder, converted into heat, would be sufficient to raise a mass of water equal to the sun and planets taken together, not less than 28,000,000 of degrees of the centigrade scale. For the sake of comparison, Professor Helmholtz mentions that the highest temperature which we can produce by the oxy-hydrogen blowpipe, which is sufficient to vaporise even platina, and which but few bodies can endure, is estimated at about 2000 degrees. Of the action of a temperature of 28,000,000 of such degrees we can form no notion. If the mass of our entire system were of pure coal, by the combustion of the whole of it only the 350th part of the above quantity would be generated.

The store of force at present possessed by our system is equivalent to immense quantities of heat. If our earth were by a sudden shock brought to rest in her orbit—which is not to be feared in the existing arrangement of our system—by such a shock a quantity of heat would be generated equal to that produced by the combustion of fourteen such earths of solid coal. Making the most unfavourable assumption as to its capacity for heat, that is, placing it equal to that of water, the mass of the earth would thereby be heated 11,200°; it would therefore be quite fused, and for the most part reduced to vapour. If, then, the earth, after having been thus brought to rest, should fall into the sun, which of course would be the case, the quantity of heat developed by the shock would be 400 times greater.

Protection From Intense Heat

The singular power which the body possesses of resisting great heats, and of breathing air of high temperatures, has at various times excited popular wonder. In the last century some curious experiments were made on this subject. Sir Joseph Banks, Dr. Solander, and Sir Charles Blagden, entered a room in which the air had a temperature of 198° Fahr., and remained ten minutes. Subsequently they entered the room separately, when Dr. Solander found the heat 210°, and Sir Joseph 211°, whilst their bodies preserved their natural degree of heat. Whenever they breathed upon a thermometer, it sank several degrees; every inspiration gave coolness to their nostrils, and their breath cooled their fingers when it reached them. Sir Charles Blagden entered an apartment when the heat was 1° or 2° above 260°, and remained eight minutes, mostly on the coolest spot, where the heat was above 240°. Though very hot, Sir Charles felt no pain: during seven minutes his breathing was good; but he then felt an oppression in his lungs, and his pulse was 144, double its ordinary quickness. To prove the heat of the room, eggs and a beefsteak were placed upon a tin frame near the thermometer, when in twenty minutes the eggs were roasted hard, and in forty-seven minutes the steak was dressed dry; and when the air was put in motion by a pair of bellows upon another steak, part of it was well done in thirteen minutes. It is remarkable, that in these experiments the same person who experienced no inconvenience from air heated to 211°, could just bear rectified spirits of wine at 130°, cooling oil at 129°, cooling water at 123°, and cooling quicksilver at 117°.

Sir Francis Chantrey, the sculptor, however, exposed himself to a temperature still higher than any yet mentioned, as described by Sir David Brewster:

The furnace which he employs for drying his moulds is about fourteen feet long, twelve feet high, and twelve feet broad. When it is raised to its highest temperature, with the doors closed, the thermometer stands at 350°, and the iron floor is red-hot. The workmen often enter it at a temperature of 340°, walking over the iron floor with wooden clogs, which are of course charred on the surface. On one occasion, Mr. Chantrey, accompanied by five or six of his friends, entered the furnace; and after remaining two minutes they brought out a thermometer which stood at 320°. Some of the party experienced sharp pains in the tips of their ears and in the septum of the nose, while others felt a pain in their eyes.—Natural Magic, 1833.

In some cases the clothing worn by the experimenters conducts away the heat. Thus, in 1828, a Spaniard entered a heated oven, at the New Tivoli, near Paris; he sang a song while a fowl was roasted by his side, he then ate the fowl and drank a bottle of wine, and on coming out his pulse beat 176°, and the thermometer was at 110° Reaumur. He then stretched himself upon a plank in the oven surrounded by lighted candles, when the mouth of the oven was closed; he remained there five minutes, and on being taken out, all the candles were extinguished and melted, and the Spaniard's pulse beat 200°. Now much of the surprise ceases when it is added that he wore wide woollen pantaloons, a loose mantle of wool, and a great quilted cap; the several materials of this clothing being bad conductors of heat.

In 1829 M. Chabert, the “Fire-King,” exhibited similar feats at the Argyll Rooms in Regent Street. He first swallowed forty grains of phosphorus, then two spoonfuls of oil at 330°, and next held his head over the fumes of sulphuric acid. He had previously provided himself with an antidote for the poison of the phosphorus. Dressed in a loose woollen coat, he then entered a heated oven, and in five minutes cooked two steaks; he then came out of the oven, when the thermometer stood at 380°. Upon another occasion, at White Conduit House, some of his feats were detected.

The scientific secret is as follows: Muscular tissue is an extremely bad conductor; and to this in a great measure the constancy of the temperature of the human body in various zones is to be attributed. To this fact also Sir Charles Blagden and Chantrey owed their safety in exposing their bodies to a high temperature; from the almost impervious character of the tissues of the body, the irritation produced was confined to the surface.