scholarly journals Bakerian Lecture :─On the variation of the specific heat of water, with experiments by a new method

1912 ◽  
Vol 86 (587) ◽  
pp. 254-257 ◽  
Keyword(s):  
Specific Heat ◽  
Experimental Evidence ◽  
Electric Current ◽  
Heat Loss ◽  
Mean Value ◽  
Mechanical Method ◽  
Order Of Accuracy ◽  
Steady Current ◽  
Differential Pair ◽  
The Mean

The question of the variation of the specific heat of water is so fundamental in calorimetry, and the results of different observers and different methods are still so discordant, that no apology is needed for the publication of fresh experimental evidence. The continuous electric method, which I carried out in conjunction with Prof. Barnes, was specially designed to avoid the main sources of error of the older methods in which mercury thermometers and open calorimeters were employed. In this method. the rise of temperature of a steady current of water, heated by a steady electric current in its passage through a fine tube hermetically scaled in a vaccumjacket, was observed with a differential pair of platinum thermometers. Errors due to lag, or to uncertainty of water-equivalent, or to evaporation or heat-loss in transference, were thus eliminated, and a higher order of accuracy was secured in the temperature measurements. The results of the continuous electric method in the case of water showed a variation of specific heat amounting to less than one half of 1 per cent. between 10° and 80°C., with a minimum at 37.6°C., followed by a very slow and steady rise. The mean value from 0° to 100°C. agreed to 1 in 2000 with the experiments of Reynolds and Moorby by the mechanical method, and the values from 5° to 35° C. agreed to a similar order of accuracy with the experiments of Rowland. But the value at 80°C. was 1 per cent. lower than that found by Lüdin's (Zürich, 1895), employing the ordinary method of mixture with an open calorimeter and mercury thermometers. Lüdin's results for the variation over the range 30° to 100°C. agreed more closely with the continuous electric method than those of any previous observers; but showed a minimum at 25°C., and a maximum at 87°C., which could not be reconciled with the experiments of Reynolds and Moorby on the mean specific heat from 0° to 100°C., or with the most probable reduction of Regnault's experiments between 110° and 190°C.

scholarly journals A recording calorimeter for explosions

1907 ◽  
Vol 79 (528) ◽  
pp. 138-154 ◽  
Keyword(s):  
Specific Heat ◽  
Heat Loss ◽  
Practical Importance ◽  
Copper Strip ◽  
Gas Engine ◽  
Coal Gas ◽  
Engine Cylinder ◽  
Solid Explosives ◽  
The Mean

The determination of the rate of loss of heat to the walls of a vessel after an explosion within it is a matter of considerable scientific interest and of practical importance. Hitherto such determinations, if we except the recent work of Dugald Clerk on the loss of heat in the gas engine cylinder, have been based upon a study of the fall of pressure during the cooling of the gases after the explosion. From the pressure the mean temperature can be deduced, and thence, if the specific heat is known, can be found the rate of heat loss at any moment. Such a calculation is, however, obviously unsatisfactory, because the only available values of the specific heat of gases at temperatures above 1500° are based upon explosion experiments, and involve doubtful assumptions as to the amount of loss before combustion is complete. Some means of determining the loss of heat at any instant without any knowledge of specific heat is therefore essential, both for finding the law of cooling of hot gases confined in a closed vessel and for placing on a satisfactory basis the specific heat values obtained from explosion experiments. I have devised a simple means of doing this which appears to be capable of considerable accuracy. It consists essentially in lining the explosion vessel as completely as possible with a continuous piece of copper strip and recording the rise of resistance of the copper strip during the progress of the explosion and the subsequent cooling. Knowing the temperature of the copper and its capacity for heat, the heat that has flowed into it from the gas may be calculated from the resistance, certain corrections being applied for the heat which the copper has lost to the insulating backing. Up to the present I have only used the apparatus for the investigation of the loss of heat after an explosion of coal gas and air, but it might, I think, be applicable, with certain modifications, to finding the heat loss during and after the combustion of solid explosives.

scholarly journals The gyro-magnetic ratio for magnetite and cobalt

1925 ◽  
Vol 108 (748) ◽  
pp. 638-642 ◽  
Keyword(s):  
Angular Momentum ◽  
Permanent Magnets ◽  
Heusler Alloys ◽  
Mean Value ◽  
Steady Current ◽  
Aluminium Wire ◽  
In Series ◽  
Iron Nickel ◽  
Average Variation ◽  
The Mean

In a recent paper a null method of determining the gyro-magnetic ratio was described, and results were given for iron, nickel and the Heusler alloys. The mean value for the three metals was found to be 0·502, with an average variation of 0·004 from the mean. The present communication extends the results to cobalt and magnetite. In this method, which was described fully in the above-mentioned paper, the specimen is suspended vertically along the axis of a solenoid, and magnetised by alternating current of the same frequency as that natural to the suspended system. Apart from disturbing couples, which can be reduced to very small dimensions, the torsional oscillations produced are due only to the angular momentum resulting from the changing magnetism of the specimen. The system is brought to rest by the current, induced by the changing magnetism, in a small “induction” helix coaxial with the specimen. This current passes through a pair of Helmholtz coils in series with an adjustable resistance, and acts on small permanent magnets rigidly fixed to an aluminium wire attached to the lower end of the specimen. When the gyro-magnetic effect is completely neutralised, we have U/M = 4 πncϕ /S i where U = the angular momentum resulting from a change M of magnetic moment, n = the number of turns per centimetre on the “induction” helix, c = torsion constant of suspension, S = neutralising resistance in the circuit of the induction helix necessary to bring the system to rest, i = steady current which when passed through the neutralisation coils produces a deflection ϕ of the permanent magnets.

scholarly journals III. On the specific heats of gases at constant volume. Part I. Air, carbon dioxide, and hydrogen

1891 ◽  
Vol 48 (292-295) ◽  
pp. 440-441 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Specific Heat ◽  
Mean Value ◽  
Constant Volume ◽  
Specific Heats ◽  
Absolute Density ◽  
The Mean ◽  
The Absolute

In this first notice the specific heats, at constant volumes, of air, carbon dioxide, and hydrogen are treated over pressures ranging from 7 to 25 atmospheres. The range of temperature is not sensibly varied. It is found that the specific heats of these gases are not constant, but are variable with the density. In the case of air the departure from constancy is small and positive; that is, the specific heat increases with increase of the density. The experiments afford directly the mean value 0·1721 for the specific heat of air at the absolute density of 0·0205, corresponding to the pressure of 19·51 atmospheres. A formula based on the variation of the specific heat with density observed in the experiments ascribes the value 0·1715 for the specific heat at the pressure of one atmosphere.

A Model of Single Molecule Magnet Behavior of the [CuIILTbIII(hfac)2]2 Cluster

2008 ◽  
Vol 273-276 ◽  
pp. 227-232
Author(s):  
S. Ostrovsky ◽  
O. Reu ◽  
A. Palii ◽  
Anatoly Yakovlevich Fishman ◽  
Valentin Yakovlevich Mitrofanov ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Experimental Evidence ◽  
Exchange Interaction ◽  
Crystal Field ◽  
Single Molecule ◽  
Magnetization Reversal ◽  
Total Angular Momentum ◽  
Mean Value ◽  
Single Molecule Magnet ◽  
The Mean

We report a model for the explanation of the single molecule magnet behavior of the [CuIILTbIII(hfac)2]2 cluster. The model takes into account the crystal field acting on the TbIII –ion and the exchange interaction between the TbIII and CuII ions. The energies of the low-lying levels are shown to increase with the decrease of the mean value of the z-projection of the total angular momentum of the cluster, thus forming a barrier for magnetization reversal that is in accordance with the experimental evidence.

scholarly journals Proposal for determining changes in entropy of semi ideal gas using mean values of temperature functions

2014 ◽  
Vol 68 (5) ◽  
pp. 615-628 ◽  
Author(s):  
Branko Pejovic ◽  
Vladan Micic ◽  
Mitar Perusic ◽  
Goran Tadic ◽  
Ljubica Vasiljevic ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Specific Heat ◽  
Internal Energy ◽  
Temperature Interval ◽  
Specific Heat Capacity ◽  
Mean Value ◽  
Ideal Gas ◽  
Mean Values ◽  
Arbitrary Temperature ◽  
The Mean

In a semi-ideal gas, entropy changes cannot be determined through the medium specific heat capacity in a manner as determined by the change of internal energy and enthalpy, i.e. the amount of heat exchanged. Taking this into account, the authors conducted two models through which it is possible to determine the change in the specific entropy of a semi-ideal gas for arbitrary temperature interval using the spread sheet method, using the mean values of the appropriate functions. The idea is to replace integration, which occurs here in evitably, with mean values of the previous functions. The models are derived based on the functional dependence of the actual specific heat capacity on the temperature. The theorem used is that of the mean value of a function as well as the mathematical properties of the definite integral. The mean value of a fractional function is determined via its integrand while the logarithmic functions were performed by applying a suitable transformation of the differential calculus. The relations derived relation, using the computer program, have enabled the design of appropriate thermodynamic tables through which it is possible to determine the change in entropy of arbitrary state changes in an efficient and rational manner, without the use of calculus or finished forms. In this way, the change in the entropy of a semi-ideal gas is determined for an arbitrary temperature interval using the method which is analogous to that applied in determining the change of internal energy and enthalpy or the amount of heat exchanged, which was the goal of the work. Verification of the proposed method for both the above functions was performed for a a few characteristic semi-ideal gases where change c(T) is significant, for the three adopted temperature intervals, for the characteristic change of state. This was compared to the results of the classical integral and the proposed method through the prepared tables. In certain or special cases, it is possible to apply the presented method also in determining the change in entropy of the real gas. Apart from that, the paper shows that the change in entropy for the observed characteristic case can be represented or graphically determined using the planimetric method of diagrams with suitably selected coordinates.

Breaking Energy of Rubbers

1967 ◽  
Vol 40 (3) ◽  
pp. 815-816
Author(s):  
K. Grosch ◽  
J. A. C. Harwood ◽  
A. R. Payne
Keyword(s):  
Energy Density ◽  
Experimental Evidence ◽  
Test Piece ◽  
Mean Value ◽  
Hysteresis Loss ◽  
Extension Rate ◽  
Extension Curve ◽  
The Mean ◽  
Breaking Energy

Abstract Recent investigations of failure of rubbers and plastics have indicated that hysteresial losses in a polymer are an important factor in fracture. This communication reports experimental evidence that the energy density at break of a polymer is amply related to the hysteresis loss in the polymer. A previously unstrained sample is stressed at a constant extension rate to rupture and the mean value of the rupture load is determined from a number of these measurements. A fresh rubber test piece is then extended under the same conditions until just before rupture, and then retracted at the same rate as was used for extending the rubber. The energy at or near break is determined by measuring the area under the load extension curve, and the hysteresis loss determined from the area between the extension and the retraction curves.

scholarly journals The variation with temperature of the specific heat of sodium in the solid and the liquid state; also a determination of its latent heat of fusion

1914 ◽  
Vol 89 (614) ◽  
pp. 561-574 ◽  
Keyword(s):  
Melting Point ◽  
Specific Heat ◽  
Latent Heat ◽  
Liquid State ◽  
Mean Value ◽  
Heat Of Fusion ◽  
Latent Heat Of Fusion ◽  
The Mean ◽  
Considerable Range

The present paper contains the results of an investigation into the variation, with temperature, of the specific heat of sodium in the solid and the liquid state; also, some determinations of its latent heat of fusion. Our knowledge of the variations of the specific heat of metals in the region of their melting point is extremely vague and hypothetical, since the methods of investigation commonly employed are only capable of giving the mean value of the specific heat over a considerable range of temperature.

scholarly journals Contributions to the theory of specific heat IV—On the calculation of the specific heat of crystals from elastic data

1935 ◽  
Vol 149 (866) ◽  
pp. 126-130 ◽  
Keyword(s):  
Specific Heat ◽  
Elastic Constants ◽  
General Problem ◽  
Elastic Waves ◽  
Low Temperatures ◽  
Equation Of Motion ◽  
Mean Value ◽  
Elastic Data ◽  
The Mean ◽  
The Waves

This paper contains a development of a method of calculating θ D values from elastic data (at low temperatures) originally given in Part II. 1—The general problem is that one is given the equation of motion of a continuum, and hence the velocity of the elastic waves as a function of the direction of the waves in a crystal and of the elastic constants; for specific heat purposes it is necessary to obtain from this equation the mean value of the velocity, and this is correlated fairly easily with the Debye θ D value.

Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 164-165
Author(s):  
Noriyuki Kuwano ◽  
Masaru Itakura ◽  
Kensuke Oki
Keyword(s):  
Electron Microscopy ◽  
Mean Value ◽  
Heavy Elements ◽  
Arc Furnace ◽  
X Ray ◽  
Long Period ◽  
Ultra High Purity ◽  
Heat Treated ◽  
Atomic Scattering ◽  
The Mean

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with <f> that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and <f> the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.

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