Joule afterwards proved (see below) that Mayer's assumption was in accordance with fact, so that his method was a sound one as far as experiment was concerned; and it was only on account of the values of the specific heats of air at constant pressure and at constant volume employed by him being very inexact that the value of the mechanical equivalent of heat obtained by Mayer was very far from the truth.
From these experiments Joule obtained 72.692 foot-pounds in the latitude of Manchester as equivalent to the amount of heat required to raise i lb of water through 1° Fahr, from the freezing point.
With an apparatus similar to the above, but smaller, made of iron and filled with mercury, Joule obtained results varying from 772.814 foot-pounds when driving weights of about 58 lb were employed to 775.352 foot-pounds when the driving weights were only about 192 lb.
By ca-sing two conical surfaces of cast-iron immersed in mercury and contained in an iron vessel to rub against one another when pressed together by a lever, Joule obtained 776.045 foot-pounds for the mechanical equivalent of heat when the heavy weights were used, and 774.93 foot-pounds with the small driving weights.
In this experiment a great noise was produced, corresponding to a loss of energy, and Joule endeavoured to determine the amount of energy necessary to produce an equal amount of sound from the string of a violoncello and to apply a corresponding correction.
Joule inferred from them that the mechanical equivalent of heat is probably about 772 foot-pounds, or, employing the centigrade scale, about 1390 foot-pounds.
Now, we know that the number of electrochemical equivalents electrolysed is proportional to the whole amount of electricity which passed through the circuit, and the product of this by the electromotive force of the battery is the work done by the latter, so that in this case also Joule showed that the heat generated was proportional to the work done.
Assuming that the whole of the energy was converted into heat, when the air was subjected to a pressure of 21.5 atmospheres Joule obtained for the mechanical equivalent of heat about 824.8 foot-pounds, and when a pressure of only 10 .
The subsequent researches of Dr Joule and Lord Kelvin (Phil.
For a long time the final result deduced by Joule by these varied and careful investigations was accepted as the standard value of the mechanical equivalent of heat.
P. Joule, and particularly R.
It has been proposed to adopt the joule, with the symbol j, as thermochemical unit for small quantities of heat, large amounts being expressed in terms of the kilojoule, Kj =100o j.
P. Joule respectively, and the author of the first formal treatise on the subject.
P. Joule (Phil.
P. Joule, who in 1842 and 1847 described some experiments which he had made upon bars of iron and steel.
In 1885 it was shown by Bidwell, in the first of a series of papers on the subject, that if the magnetizing force is pushed beyond the point at which Joule discontinued his experiments, the extension of the bar does not remain unchanged, but becomes gradually less and less, until the bar, after first returning to its original length, ultimately becomes actually shorter than when in the unmagnetized condition.
P. Joule, Scientific Papers, pp. 46, 235; A.
] Joule and others experimented with hardened steel, but failed to find a key to the results they obtained, which are rather complex, and have been thought to be inconsistent.
Joule also made experiments upon iron wires under tension, and drew the erroneous inference (which has been often quoted as if it were a demonstrated fact) that under a certain critical tension (differing for different specimens of iron but independent of the magnetizing force) magnetization would produce no effect whatever upon the dimensions of the wire.
Bidwell's results for iron and nickel were confirmed, and it was further shown that the elongation of nickel-steel was very greatly diminished by tension; when 2 Joule believed that the volume was unchanged.
Joule (1845) was the first to prove it approximately by direct experiment, but did not see his way to reconcile Carnot's principle, as stated by Clapeyron, with the mechanical theory.
This most fundamental point was finally settled by a more delicate test, devised by Lord Kelvin, and carried out in conjunction with Joule (1854), which showed that the fundamental assumption W =H in isothermal expansion was very nearly true for permanent gases, and that F'(t) must therefore vary very nearly as J/T.
This test was applied by Joule in the well-known experiment in which he allowed a gas to expand from one vessel to another in a calorimeter without doing external work.
Method of Joule and Thomson.
As the result of their experiments on actual gases (air, hydrogen, and C02), Joule and Thomson (Phil.
Experiments by Natanson on CO 2 at 17° C. confirm those of Joule and Thomson, but show a slight increase of the ratio do/dp at higher pressures, which is otherwise rendered probable by the form of the isothermals as determined by Andrews and Amagat.
Modified Joule-Thomson Equation.
The value of the co-aggregation volume, c, at any temperature, assuming equation (17), may be found by observing the deviations from Boyle's law and by experiments on the Joule-Thomson effect.
In the modified Joule-Thomson equation (17), both c and n have simple theoretical interpretations, and it is possible to express the thermodynamical properties of the substance in terms of them by means of reasonably simple formulae.
Of greater interest, particularly from a historical point of view, are the original papers of Joule, Thomson and Rankine, some of which have been reprinted in a collected form.
P. Joule with the perforated piston and with the friction of water and mercury.
(If the molecules of air at normal temperature and pressure were arranged in cubical order, the edge of each cube would be about 2.9 X I o - ' cms.; the average diameter of a molecule in air is 2.8X Io - 8 cms.) Further and very important evidence as to the nature of the gaseous state of matter is provided by the experiments of Joule and Kelvin.
This inquiry yielded (in 1867) the result 783, and this Joule himself was inclined to regard as more accurate than his old determination by the frictional method; the latter, however, was repeated with every precaution, and again indicated 772.55 foot-pounds as the quantity of work that must be expended at sea-level in the latitude of Greenwich in order to raise the temperature of one pound of water, weighed in vacuo, from 60 to 61° F.
In addition, numerous other researches stand to Joule's credit - the work done in compressing gases and the thermal changes they undergo when forced under pressure through small apertures (with Lord Kelvin), the change of volume on solution, the change of temperature produced by the longitudinal extension and compression of solids, &c. It was during the experiments involved by the first of these inquiries that Joule was incidentally led to appreciate the value of surface condensation in increasing the efficiency of the steam engine.
Meters intended to measure electric energy (which is really the subject of the sale and purchase) are called joule meters, or generally watt-hour meters.
P. Joule after years of patient labour in direct experimenting.
He next experimented with a highpressure hydrogen jet by which low temperatures were realized through the Thomson-Joule effect, and the successful results thus obtained led him to build at the Royal Institution the large refrigerating machine by which in 1898 hydrogen was for the first time collected in the liquid state, its solidification following in 1899.
A more convenient unit of work or energy, in practice, on account of the smallness of the erg, is the joule, which is equal to 10.7 ergs, or one watt-second of electrical energy.
On account of its practical convenience, and its close relation to the international electrical units, the joule has been recommended by the British Association for adoption as the absolute unit of heat.
The earlier work of Joule is now chiefly of historical interest, but his later measurements in 1878, which were undertaken on a larger scale, adopting G.
(I.) The Method Corresponding To The Expression Cr T Was Adopted By Joule And By Most Of The Early Experimentalists.
The size of jar commonly known as a quart size may have a capacity from 4 o 0 th to s 00 oth of a microfarad, and if charged to 20,000 volts stores up energy from a quarter to half a joule or from -ths to Iths of a foot-pound.
The ideal method of determining by direct experiment the relation between the total heat and the specific heat of a vapour is that of Joule and Thomson, which is more commonly known in connexion with steam as the method of the throttling calorimeter.
Assuming dH/do = 0.305 for saturated steam, he found that S was nearly independent of the pressure at constant temperature, but that it varied with the temperature from o 387 at 100° C. to o 665 at 160° C. Writing Q for the Joule-Thomson " cooling effect," dO/dp, or the slope BC/AC of the line of constant total heat, he found that Q was nearly independent of the pressure at constant temperature, a result which agrees with that of Joule and Thomson for air and COs; but that it varied with the temperature as (1/0) 3.8 instead of (i/0) 2.
In order to correct this equation for the deviations of the vapour from the ideal state at higher temperatures and pressures, the simplest method is to assume a modified equation of the Joule-Thomson type (Thermodynamics, equation (17)), which has been shown to represent satisfactorily the behaviour of other gases and vapours at moderate pressures.
The deviations from the ideal volume may also be deduced by the method of Joule and Thomson.
But in order to deduce the values of c by the Joule-Thomson method, it is necessary to assume an empirical formula, and the type c=co(6019) n is chosen as being the simplest.
P. Joule found that magnetization did not increase proportionately with the current, but reached a maximum (Sturgeon's Annals of Electricity, 1839, 4).
Electric magnets of great power were soon constructed in this manner by Sturgeon, Joule, Henry, Faraday and Brewster.
P. Joule had assumed to be the same at all temperatures.