ment and Desormes regards carbonic acid, which, being reduced to the standard of weights, gives a specific heat compared to air of about 0.987 to 1.000, while oxygen is only 0.9000. The former tables of Crawford and Dalton give the specific heat of oxygen 2-65, and of carbonic acid 0.586, compared to air 1·000. And, upon these very erroneous numbers, they reared their hypothetical fabric of latent heat, combustion, and the animal temperature. We see from the experiments on air, at different densities, that its specific heat diminishes in a much slower rate than its specific gravity. When air is expanded to a quadruple volume, its specific heat becomes 0.540, and, when expanded to eight times the volume, its specific heat is 0.368. The densities in the geometrical progression 1,,,, correspond nearly to the specific heats in the arithmetical series 5, 4, 3, 2. Hence also the specific heat of atmospherical air, and of probably all gases, considered in the ratio of its weight or mass, diminishes as the density increases. On the principle of the increase of specific heat, relative to its mass, has been explained the long observed phenomenon of the intense cold which prevails on the tops of mountains, and generally in the upper regions of the atmosphere; and also that of the prodigious evolution of heat, when air is forcibly condensed. According to M. Gay Lussac, a condensation of volume, amounting to four-fifths, is sufficient to ignite tinder. If a syringe of glass be used, a vivid flash of light is seen to accompany the condensation. The above products, which express the capacities of the different atoms, approach so near equality, that the slight differences must be owing to slight errors, either in the measurement of the capacities, or in the chemical analyses, especially if we consider, that, in certain cases, these errors, derived from these two sources, may be on the same side, and consequently be found multiplied in the result. Each atom of these simple bodies seems, therefore, as was formerly stated, to have the same capacity for heat. The question may here be asked, Whether a body, in cooling a certain thermometric range at a high temperature, gives out the same quantity of heat that it does in cooling through the same range at a lower temperature? No means seem better adapted for solving this problem, than to measure the refrigeration produced, by the same weights of ice, on uniform weights of water, at different temperatures. Mr. Dalton found in this way, that 176.5° expresses the number of degrees of temperature, such as are found between 200° and 212° of the old or common scale, entering into ice of 32° to convert it into water of 32°; 150° of the same scale, between 122° and 130°, suffice for the same effect; and between 45° and 50°, 128° are adequate to the conversion of the same ice into water. These three resulting numbers (128, 150, 176·5), are nearly as 5, 6, 7. Hence it follows, that as much heat is necessary to raise water 5° in the lower part of the old scale, as is required to raise it 7° in the higher, and 6° in the middle.' See his New System of Chemical Philosophy, vol. i. p. 53. < Mr. Dalton, however,' says Dr. Ure, 'instead of adopting the obvious conclusion, that the capacity of water for heat is greater at lower than it is at higher temperatures, and that therefore a smaller number of degrees at the former should melt as much ice as a great number at the latter, ascribes the deviation denoted by these numbers, 5, 6, and 7, to the gross errors of the ordinary thermometric graduation, which he considers so excessive, as not only to equal, but greatly to overbalance the really increased specific heat or capacity of water; which, viewed in itself, he conceives would have exhibited opposite experimental results. That our old, and, according to his notions, obsolete thermometric scale, has no such prodigious deviation from truth, is, I believe, now fully admitted by chemical philosophers; and therefore the only legitimate inference from these very experiments of Mr. Dalton is the decreasing capacity of water, with the increase of its temperature. It deserves to be remarked, that my experiments on the relative times of cooling a globe of glass, successively filled with water, oil of vitriol, common oil, and oil of turpentine, give exactly the same results as Mr. Dalton had derived from mixtures of two ounces of ice with sixty of water, at different temperatures. This concurrence is the more satisfactory, since, when my paper on the specific heats of the above bodies, published in the Annals of Philosophy for October 1817, was written, I had no recollection of Mr. Dalton's experiments.' TABLE V.-Of Capacities for Heat. 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 0 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. PART II. 332-29 318-2 324.8 329.3. 320.0 317-9 322.1 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 many 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, exterior to the heating apparatus, when the rod was elongated by heat, the displacement of the microscopes could be 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, trical apparatus of a peculiar construction, for he tells us, many experiments with a micromemeasuring 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 Dimensions which a bar takes at 2120, whose length at 32° is 1·000000. Smeaton, 1.00083333 Dilatation in Vulgar Fractions. Glass tube, Do. Do. Deluc's mean, Do. Dulong and Petit, 1.00086130 Do. Lavoisier and Laplace, Plate glass, Do. do. Do. crown glass, Do. 1.00089760 1090 Do. Do. and glass, TABLE I.-Linear Dilatation of Solids by Heat.-Continued Dimensions which a bar takes at 2120, whose length at 32° is 1·000000. Dilatation in Vulgar Fractions. 1 Lavoisier and Laplace, 1.00107875 127 Do. do. 1.00107956 928 Do. do. 1.00136900 Do. do. 1.00138600 Do. do. 1.00123956 B07 Troughton, 1.00118980 Smeaton, 1.00122500 TABLE II.-Dilatation of the volume of Liquids by being heated from 32° to 212°. Dr. Young, in his valuable Catalogue Raisonnée, Natural Philosophy, vol. ii. p. 391, gives the following table of the expansions of water, constructed from a collation of experiments by Gilpin, Kirwan, and Achard. He says that the degrees of Fahrenheit's thermometer, reckoning either way from 39°, being called f, the expansion of water is nearly expressed by 22f2 (1002f) in 10 millionths; and the diminution of the sp. gr. by 0000022f" *00000000472f3. This equation, as well as the table, is very important for the reduction of specific gravities of bodies, taken by weighing them in water. 0-05198 -P 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 100° some to apply than the above rule. Vapors, 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. 173 126 96 Sulphuret of carb. 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. is 0'375 180 0.375 Mr. Dalton has the merit of having first proved that the expansions of all aëriform 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 0.002083; and for the centigrade 0.00375= 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 217; for × 60= {%=}; and 3, 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 trouble scale it is 100 VOL. XI. 266'6" 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 |