The capacity of iron was determined at the elevation of their temperature, that it becomes four following intervals: From 0° to 100°, the capacity is 0.1098 0 to 200 O to 300 0 to 350 0.1150 0.1218 'If we estimate,' continues Dr. Ure, the temperatures, as some philosophers have proposed, by the ratios of the quantities of heat which the same body gives out in cooling to a determinate temperature, in order that this calculation be exact, it would be necessary that the body in cooling, for example, from 300° to 0°, should give out three times as much heat as in cooling from 100° to 0°. But it will give out more than three times as much, because the capacities are increasing. We should therefore find too high a temperature. We exhibit in the following table the temperatures that would be deduced by employing the different metals contained in the preceding table. We must suppose that they have been all placed in the same liquid bath at 300°, measured by an air thermometer. Iron Mercury Zinc PART II. 332.2° 318.2 328.5 329.3 320.0 317.9 OF THE GENERAL SYMPATHIES OF HEAT WITH THE DIFFERENT FORMS OF MATTER. The effects of heat are either transient and physical, or permanent and chemical, inducing a durable change in the constitution of bodies. The latter effect we have already treated of in our article COMBUSTION. The first is to be discussed here; and divides itself into the two heads, of changes in the volume of bodies while they retain their form, and changes in the state of bodies. an easy task to ascertain within certain limits the augmentation of volume which liquids and gases suffer through a moderate thermometric range. We have only to enclose them in a glass vessel of a proper form, and expose it to heat. But to determine their expansion with final accuracy, and free the results from the errors arising from the unequable expansion of the recipient, is a problem of no small difficulty. It seems, however, after inany vain attempts by preceding experimenters, to have been finally solved by MM. Dulong and Petit. The expansion of solids had been previously measured with considerable accuracy by several philosophers, particularly by Smeaton, Roy, Ramsden, and Troughton, in this country, and Lavoisier and Laplace in France. The method devised by general Roy, and executed by him in conjunction with Ramsden, deserves the preference. The metallic or other rod, the subject of experiment, was placed horizontally in a rectangular trough of water, which could be conveniently heated. At any aliquot distance on the rod, two micrometer microscopes were attached at right angles, so that each being adjusted at first to two immoveable points, ex:erior to the heating apparatus, when the rod was elongated by heat, the displacement of the microscopes could he determined to a very minute quantity, to the twenty or thirty thousandth of an inch, by the micrometrical mechanism. Dr. Ure, in the years 1812 and 1813, made, he tells us, many experiments with a micrometrical apparatus of a peculiar construction, for measuring the dilatation of solids. I was particularly perplexed,' he says, 'with the rods of zinc, which, after innumerable trials, I finally found to elongate permanently by being alternately heated and cooled. It would seem that the plates composing this metal, in sliding over each other by the expansive force of heat, present such an adhesive friction as to prevent their entire retraction. It would be desirable to know the limit of this effect, and to see what other metals are subject to the same change. I hope to be able, ere long, to finish these pyrometrical researches.' The doctor then gives us the following copious tables of dilatations, compiled from the best experiments :TABLE I.-Linear Dilatation of Solids by Heat. 1. The successive increments of volume which bodies receive with successive increments of temperature, have been the subjects of innumerable researches. The expansion of fluids is so much greater than that of solids, by the same HEAT. TABLE I.-Linear Dilatation of Solids by Heat.-Continued Dimensions which a bar takes at 2120, whose length at 320 is 1.000000. 111 1.00108300 Dilatation in Vulgar Fractions. Cast iron prism, Roy, 1-00110940 Cast iron, Lavoisier, by Dr. Young, 1.00111111 Steel, Troughton, 1.00118990 Steel rod, Roy, 1.00114470 Blistered steel, Phil. Trans. 1795, 428, 1:00112500 Smeaton, 1.00115000 Lavoisier and Laplace, Do. do. do. Do. do. Do. tempered yellow, Do. do. 1.00136900 Do. do. do. Do. do. Do. do. do. at a higher heat, 1.00123956 607 Steel, Troughton, 1.00118980 Hard steel, Smeaton, 1.00122500 Annealed steel, Muschenbroek, 1.00122000 Tempered steel. Do. 1.00137000 Borda, 1.00115600 Iron, Smeaton, 1.00125800 Lavoisier and Laplace, 1.00122045 Round iron, wire-drawn, Do. do. 1.90123504 Iron wire, Troughton, 1.00144010 Iron, Dulong and Petit, Smeaton, Ellicot, by comparison, Do. do. 1.00171222 1.00191880 Do. Duleng and Petit, 1.00171821 ་ྒུ--རཱྀ- -- Brass, Borda, 1.00178300 Do. Lavoisier and Laplace, 1.00186671 Do. Do. do. 1.04188971 Brass scale, supposed from Hamburg, Roy, 1.00185540 Cast brass, Smeaton, 1.00187500 English plate-brass, in rod, Roy, 1-00189280 Do. do. in a trough form, Do. 1.00189490 Brass, Troughton, 1.00191880 Brass wire, Smeaton, 1-00193000 Brass, Muschenbroek, 1.00216000 Copper 8, tin 1, Smeaton, 1.00181700 Silver, Herbert, 1.00189000 Do. Ellicot, by comparison, 1.0021000 Do. Muschenbroek, 1.00212000 Do. of cupel, Do. Paris standard, Do. Lavoisier and Laplace, Silver, Troughton, 1.00190974 Brass 16, tin 1, Smeaton, 1.00190800 Speculum metal, Do. 1.00193300 Spelter solder; brass 2, zinc 1, Do. 1.00205800 Malacca tin, Lavoisier and Laplace, 1.00193765 Tin from Falmouth, Do. do. 1.00217298 ཊྛོ- Fine pewter, Smeaton, 1.00228300 Grain tin, Do. 1.00248300 Tin, Muschenbroek, 1.00284000 Soft solder; lead 2, tin 1, Smeaton, 1.00250800 Zinc 8, tin 1, a little hammered, Do 1.00269200 Lead, Lavoisier and Laplace, Do. Smeaton, 1.00286700 Zinc, Do. 1.00294200 Zinc, hammered out inch per foot, Do. 1.00301100 Glass, from 32° to 212°, Dulong and Petit 1.00086130 Do. from 212°, to 392°, Do. do. Do. from 392°, to 572°, The last two measurements by an air thermometer. TABLE II.—Dilatation of the volume of Liquids by being heated from 32° to 212°. Expansion. M. Gay Lussac has lately endeavoured to discover some law which should correspond with the rate of dilatation of different liquids by heat. For this purpose, instead of comparing the dilatations of different liquids, above or below a temperature uniform for all, he set out from a point variable with regard to temperature, but uniform as to the cohesion of the particles of the bodies; namely, from the point at which each liquid boils under a given pressure. Among those which he examined, he found two which dilate equally from that point, viz. alcohol and sulphuret of carbon, of which the former boils at 173.14°, the latter at 115.9°, Fahrenheit. The other liquids did not present, in this respect, the same resemblance. Another analogy of the above two liquids is, that the same volume of each gives, at its boiling point, under the same atmospheric pressure, the same volume of vapor; or, in other words, that the densities of their vapors are to each other as those of the liquids at their respective boiling temperatures. The following table shows the results of this distinguished chemist : 0.00299 by expt. calculated. by expt. calculated. by expt. calculated. by expt. calculated. Their respective boiling points are: Water Alcohol Sulphuret of carb. Sulphuric ether some to apply than the above rule. Vapors, 100° Cent. 212° F. when heated out of contact of their respective liquids, obey the same law as gases; a discovery due to M. Gay Lussac. 78.41 46.60 35.66 173 126 96 The experiments were made in thermometer vessels hermetically sealed. Alcohol, at 78-41° cent., produces 488-3 its volume of vapor. Sulphuret of carbon, at 46-60° cent., produces 491.1 its volume of vapor. Ether, at 35-66° cent., produces 285.9 its volume of vapor. Water, at 100-00° cent., produces 1633 1 its volume of vapor. 180 scale it is 0'375 Mr. Dalton has the merit of having first proved that the expansions of all aeriform bodies, when insulated from liquids, are uniform by the same increase of temperature; a fact of great importance to practical chemistry, which was fully verified by the independent and equally original researches of M. Gay Lussac on the subject, with a more refined and exact apparatus. The latter philosopher demonstrated that 100 in volume at 32° Fahrenheit, or 0° cent., became 1-375 at 212° Fahrenheit, or 100° cent. Hence the increment of bulk for each degree Fahrenheit is 9375 0.002083; and for the centigrade 0.00375 = L. To reduce any volume of gas, therefore, to the bulk it would Occupy at any standard temperature, we must multiply the thermometric difference in degrees of Fahrenheit by 0·002083, or, subtracting the product from the given volume, if the gas be heated above, but adding it, if the gas be cooled below, the standard temperature. Thus twentyfive cubic inches at 120° Farenheit will at 60° occupy a volume of 213; for × 60==}; and 34, which, taken from 25, leaves 217. A table of reduction will be found under GAS. When the table is expressed decimally, indeed, to six or seven figures, it becomes more troubleVOL. XI. 100 2666 2. Of the change of state produced in bodies by caloric.-The three forms of matter, the solid, liquid, and gaseous, seem immediately referrible to the power of heat, modifying, balancing, or subduing cohesive attraction. The system of the world presents magnificent effects of attraction dependent on figure. Such are the phenomena of nutation and the precession of the equinoxes, produced by the attractions of the sun and moon on the flattened spheroid of the earth. These sublime phenomena would not have existed had the earth been a sphere: they are connected with its oblateness and rotation, in a manner which may be mathematically deduced, and subjected to calculation. The investigation shows, that this part of the attraction dependent on figure decreases more rapidly than the principal force. The latter diminishes as the square of the distance; the part dependent on figure diminishes as the cube of the distance. Thus also, in the attractions which hold the parts of bodies united, we ought to expect an analogous difference to occur. Hence the force of crystallisation may be subdued, before the principal attractive force is overcome. When the particles are brought to this distance, they will be indifferent to all the positions which they can assume round their centre of gravity; this will constitute the liquid condition. We must now content ourselves with stating the results as much as possible in a tabular form. TABLE of the Concreting or Congealing Tem- 46° 46 The solidifying temperature of the bodies above tallow, in the table, is usually called their freezing or congealing point; and of tallow, and the bodies below it, the fusing or melting point. Now, though these temperatures be stated, opposite to some of the articles, to fractions of a thermometric degree, it must be observed, that various circumstances modify the concreting point of the liquids, through several degrees; but the liquefying points of the same bodies, when once solidified, are uniform and fixed to the preceding temperatures. Water, all crystallisable solutions, and the three metals, cast-iron, bismuth, and antimony expand considerably in volume, at the instant of solidification. The greatest obstacles cannot resist the exertion of this expansive force. Thus, glass bottles, trunks of trees, iron and lead pipes, even mountain rocks, are burst by the dilatation of the water in their cavities, when it is converted into ice. In the same way our pavements are raised in winter. Major Williams of Quebec burst bombs, which were filled with water and plugged up, by exposing them to a freezing cold. The beneficial operation of this cause is exemplified in the comminution or loosening the texture of dense clay soils, by the winter's frost, whereby the delicate fibres of plants can easily penetrate them. There is an important circumstance occurs in the preceding experiments on the sudden congelation of a body kept liquid below its usual congealing temperature, to which we must now advert. The mass, at the moment its crystallisation commences, rises in temperature to the term marked in the preceding table, whatever number of degrees it may have previously sunk below it. Suppose a globe of water suspended in an atmosphere at 21° Fahrenheit; the liquid will cool and remain stationary at this temperature, till vibration of the vessel, or contact of a spicula of ice, determines its concretion, when it instantly becomes 11° hotter than the surrounding medium. We owe the explanation of this fact, and its extension to many analogous chemical phenomena, to the sagacity of Dr. Black. His truly philosophical mind was particularly struck by the slowness with which a mass of ice liquefies when placed in a genial atmosphere. A lump of ice at 22° freely suspended in a room heated at 50°, which will rise to 32° in five minutes, will take 14 times 5, or seventy minutes to melt into water, whose temperature will be only 32°. Dr. Black suspended in an apartment two glass globules of the same size alongside of each other, one of which was filled with ice at 32°, the other with water at 33°. In half an hour the water had risen to 40°; but it took ten hours and a half to liquefy the ice, and heat the resulting water to 40°. Both these experiments concur, therefore, in showing that the fusion of ice is accompanied with the expenditure of 140° of calorific energy, which have no effect on the thermometer. For the first experiment tells us that 10° of heat entered the ice in the space of five minutes, and yet fourteen times that period passed in its liquefaction. second experiment shows that 7° of heat entered the globes in half an hour; but twenty-one half hours were required for the fusion of the ice, and for heating of its water to 40°. If from the product of 7 into 21 147, we subtract the 7° which the water was above 33°, we have 140° as before. But the most simple and decisive experiment is to mingle a pound of ice in small fragments with a pound of water at 172°. Its liquefaction is instantly accomplished, but the temperature of the mixture is only 32°. Therefore, 140° of heat seem to have disappeared. Had we mixed a pound of ice-cold water with a pound of water at 172°, the resulting temperature would have been 102°, proving that the 70° The |