190 MECHANICS, PHYSICS, AND CHEMISTRY. TRANSLATED FOR THE JOURNAL OF THE FRANKLIN INSTITUTE. Account of the Experiments to determine the Principal Laws and Numerical TENTH MEMOIR. By M. V. On the Specific Heat of Liquid Water at Different Temperatures. (Continued from page 119.) The experiments described in the preceding memoirs, were intended to determine the quantities of heat which it is necessary to give to 1 kilogramme (or one pound) of liquid water at 0°, to convert it into saturated steam under different pressures. But these quantities are composed of two parts; the first is the quantity of heat necessary to raise the temperature of the water from 0° to the degree at which the change takes place; and the second is that which is absorbed in the latent state by the passage of the liquid water to the state of vapor. Philosophers assume generally that the first portion is represented by the number which expresses the temperature of the steam; in other words, they assume that the calorific capacity of liquid water is constant: that is, that it requires the same quantity of heat to raise one kilogramme (or one pound) of water from 0° to 1°, as to raise it from 100° to 101°, or from 200° to 2010. M. Regnault has shewn, however, (Ann. de Chimie et de Phys., 3e serie, tom. 1x, p. 324,) that the specific heat of certain liquids augments rapidly with the temperature. He found, in fact, that the mean specific heat of the oil of turpentine, which is about 0-420 between 15° and 20°, already becomes 0.467 between 20° and 100°. (Ann. de Chimie, tom. Ix, pp. 342 and 347.) It is probable that increase of calorific capacity is especially very notable for liquids whose coefficient of dilatation is considerable, and that it increases rapidly with the temperature; we ought, then, to expect to find a much less variation for water than for the oil of turpentine. In a former memoir upon the specific heats of simple and compound bodies, (Ann. de Chim. et de Phys., 2e serie, tom. LXXш, p. 35,) M. Regnault found for the mean specific heat of water between 15° and 100°, compared with that of the same liquid between 10° and 15°, (this latter being supposed 1.000,) the two numbers 1.00709 and 1.0089. These numbers, though intended for another purpose, suffice to shew that the specific heat of water does not undergo any notable augmentation between 10° and 100°. He now proposes to determine the same element up to the temperature 200°, (392 Fah.,) and for this purpose he devised the following mode of operating, which appears to him to be fitted to give accurate results. The side of the boiler which was used in the experiments upon the elasticity of steam, was bored, and a tube was inserted, which, entering the boiler, bent down and extended to within 1 decim. (4 in.) of the bottom, where it opened into the boiler by a vertical opening. On the outside of the boiler, there was adjusted upon this tube a carefully made stop-cock, having a clear passage of 10 mm. (0-4 in.) From the stop-cock proceeded a brass tube, which entered the side of a large vessel made of galvanized sheet iron, which was used as a calorimeter. The tube was closed at its extremity, but was pierced with a great number of small holes. The calorimeter had on its top a large tubulure, into which was cemented an open graduated glass tube. In another opening in the cover was cemented a very sensitive thermometer. Below, it had a stop-cock by which it could be completely emptied, and connected with it was a glass gauge-tube, by which the height of the water in the vessel could be, at any moment, accurately ascertained. It was also provided with a properly adjusted agitator, by which the water could be continually stirred, and was supported upon an iron tripod. The tube passing from the boiler to the calorimeter, and the ring by which the calorimeter was supported upon its tripod, were carefully wrapped with woolen listing. The calorimeter was placed as near the boiler as possible, and was protected from the radiant heat by a semi-cylindrical screen, formed of a tinned iron box, through which a stream of cold water was continually kept passing. The weight of water which filled the calorimeter at different temperatures to the zero of the graduated glass tube, was carefully determined, and the value of each division of the tube ascertained. The method of operating is as follows: The boiler being filled about three-fourths full of water, it is put into communication with the air reservoir, and the pressure brought to about that corresponding to the temperature at which the experiment is to be made. The water is then made to boil, and when the boiler has arrived at uniformity of temperature, as indicated by its thermometers, the calorimeter is adjusted: that is to say, it is filled with water up to one of the divisions of the glass tube; the water is then agitated so as to give it an uniform temperature, and for five minutes the rise of temperature is carefully watched, for the purpose of ascertaining the corrections for the heating by the conducting power of the tube, and by contact with the surrounding air. A globe holding about 10 litres, (2.5 galls.,) is then placed under the stop-cock of the calorimeter, and nearly filled with water which is carefully weighed. As the weight of water originally placed in the apparatus was determined, the quantity remaining is perfectly known. The temperature of the water in the calorimeter is now very carefully noted, and the stop-cock communicating with the boiler being then opened, the excess of pressure forces the hot water more or less rapidly into the calorimeter, and the calorimeter begins to fill again. The height of the water is observed in the side gauge, and when it has risen nearly to the insertion of the graduated glass tube on top, the stopcock is nearly closed and the water suffered to enter very slowly, to avoid overflow, until it has reached a proper point on the tube. The stop-cock is then entirely closed, and the water being all this time continually stirred, the thermometer is closely watched until it has attained a maximum temperature; the division of the glass tube to which the water rises is then immediately read. As the contents of the calorimeter have been already carefully gauged at all temperatures within the limits of the experiments, the quantity of water which has entered from the boiler is known. The operation is very quick, especially at first, since ths of the water enters during a half minute. Sometimes, in place of allowing the calorimeter to fill entirely from the boiler, the stop-cock was entirely closed when the water had risen nearly to the insertion of the tube, and the instrument was then filled by pouring into it a known quantity of water, at a known temperature. In either way, the quantity of water entering from the boiler became known. The thermometer, after reaching a maximum, begins to fall, and is again watched for five minutes, for the purpose of getting the correction for the cooling by radiation, and by contact with air. This method gives all the data required for calculating the specific heat of water, between the temperature of the water in the boiler and the final temperature of the calori meter. A small correction is required for the mercurial column of the thermometer which projects above its cover. The greatest cause of uncertainty arises from the difficulty of observing accurately the level of the water in the glass tube. As the water of the calorimeter becomes rapidly heated, it gives up the air which it held in solution. This air rises in bubbles, and the water has to be stirred for a long time, to be certain that they are entirely discharged and do not alter the level in the glass tube. Experiments, given at the end of the memoir on "The Compressibility of Liquids," (vol. xvi, p. 334,) make it extremely probable that any heat absorbed by the water, in its sudden expansion from the pressure of the boiler to that of the atmosphere, in entering the calorimeter, may be entirely negligable. M. Regnault then gives a table of his experiments, from which it appears that the specific heat of water from 0° to 30° (32° to 86° F.) being 1000, "30° to 110° (86° to 230° F.) it is 1005, and 30° to 190° (86° to 374° F.) it is 1015. The increase is, therefore, so very small, that in most cases it may be neglected, especially if the heat does not surpass 100°. (212° F.) M. Regnault then calculates a formula of interpolation of the form Q=T+AT+BT3 where Q=the number of units of heat which a kilogramme of water, heated to a temperature T, abandons, in cooling to 0°. The unit of heat being the quantity of heat which 1 kilogramme of water at 0° absorbs in rising 1o in temperature. From his experiments, he calculates the constants A & B, and the formula becomes Q=T+0.00002T2 +0·0000003T3. The quantity of heat which a quantity of water, at the temperature T, absorbs in rising 1° of temperature is given by the formula, By means of these formulæ the following table was calculated, giving for every ten degrees of temperature Centigrade, as noted by the air thermometer, the quantities of heat (Q) which a kilogramme (or pound) of water, heated to the temperature T, gives out in descending to 0°, and the quantities of heat which a kilogramme (or pound) of water at To, absorbs when its temperature becomes (T+dT)°. If from the total quantities of heat which a kilogramme of saturated steam at To, abandons in passing to the condition of liquid water at 0°, (quantities which are given in the table below,) we subtract the quantities (Q) of heat which a kilogramme of liquid water at To, abandons in descending to 0°, we shall obtain the quantities of heat which a kilogramme of saturated steam, at the temperature To, abandons in passing to the state of liquid water at the same temperature. These latter quantities, which are commonly called the latent heats of steam, we give in the last column of the table. Table of the Specific Heats of Liquid Water. The atmosphere rises above us with its cathedral dome arching towards the heaven of which it is the most familiar synonyme and symbol. It floats around us like that grand object which the Apostle John saw in his vision: "a sea of glass like unto crystal." So massive is it that, when it begins to stir, it tosses about great ships like playthings, and sweeps cities and forests like snow flakes to destruction before it. And yet it is so mobile, that we have lived years in it before we can be persuaded it exists at all, VOL. XVII-THIRD SERIES-No. 3.-MARCH, 1849. 17 and the great bulk of mankind never realize the truth that they are bathed in an ocean of air. Its weight is so enormous that iron shivers before it like glass, yet a soap-ball sails through it with impunity, and the tiniest insect waves it with its wings. It ministers lavishly to all the senses.— We touch it not, but it touches us: its warm south wind brings back color to the pale face of the invalid: its cool west winds refresh the fevered brow, and make the blood mantle in our cheeks: even its north blasts brace into new vigor the hardened children of our rugged clime. The eye is indebted to it for all the magnificence of sunrise, the full brightness of mid-day, the chastened radiance of the gloaming, and the clouds that cradle near the setting sun. But for it the rainbow would want its triumphal arch, and the winds would not send their fleecy messengers on errands round the heavens. The cold ether would not shed its snow feathers on the earth, nor would drops of dew gather on the flowers. The kindly rain would never fall-hail, storm, nor fog diversify the face of the sky. Our naked globe would turn its tanned unshadowed forehead to the sun, and one dreary monotonous blaze of light and heat dazzle and burn up all things. Were there no atmosphere, the evening sun would in a moment set, and, without warning, plunge the earth in darkness. But the air keeps in her hand a sheaf of his rays, and lets them slip but slowly through her fingers; so that the shadows of evening gather by degrees, and the flowers have time to bow their heads, and each creature space to find a place of rest and nestle to repose. In the morning the garish sun would, at one bound, burst from the bosom of night and blaze above the horizon; but the air watches for his coming, and sends at first but one little ray to announce his approach, and then another, and by and by a handful, and so gently draws aside the curtain of night, and showly lets the light fall on the face of the sleeping earth, till her eye-lids open, and, like man, she goeth forth again to her labor until the evening.-Quarterly Review. Lond. Athen., Dec. 1848. On the Crystalline Polarity of Bismuth and other bodies, and on its Relation to the Magnetic Form of Force. From the Bakerian Lecture delivered before the Royal Society, London, by DR. FARADAY. The author states that in preparing small cylinders of bismuth, by casting them in glass tubes, he had often been embarrassed by the anomalous magnetic results which they gave, and that having determined to investigate the matter closely, it ended in a reference of the effects to the crystalline condition of the bismuth, which may be thus briefly stated. If bismuth be crystallized in the ordinary way, and then a crystal, or a group of symmetric crystals, be selected and suspended in the magnetic held between horizontal poles, it immediately either points in a given direction or vibrates about that position, as a small magnetic needle would do, and if disturbed from this position it returns to it. On re-suspending the crystal so that the horizontal line which is transverse to the magnetic axis shall become the vertical line, the crystal then points with its maximum degree of force. If it be again re-suspended, so that the line parallel to the magnetic axis be rendered vertical, the crystal loses all directive |