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conductivity

when exposed to the action of light its electric conductivity increases.

8125The electrical conductivity of sea-water increases with the salinity; at 59° F.

3710The conductivity gives us the amount of electricity conveyed per second under a definite electromotive force.

2912Its conductivity for heat has been variously given as 103 (C. M.

2315For data concerning the conductivity of the organic bases see G.

1910For example, a rise in temperature of the bath causes an increase in its conductivity, so that a lower E.M.F.

1511The principal points of difference are that (I) the magnetic permeability, unlike the electric conductivity, which is independent of the strength of the current, is not in general constant; (2) there is no perfect insulator for magnetic induction, which will pass more or less freely through all known substances.

1311Towards the end of his life he was occupied with experimental inquiries into the laws of the conduction of heat in bars, and his last piece of work was to show that the thermal conductivity of iron diminishes with increase of temperature.

1110Charcoal is valuable for its infusibility and low conductivity for heat (allowing substances to be strongly heated upon it), and for its powerful reducing properties; so that it is chiefly employed in testing the fusibility of minerals and in reduction.

111119; but this would probably recover less heat than the continuous system, first, because it transfers the heat from flame to metal indirectly instead of directly; and, second, because the brickwork of the Siemens system is probably a poorer heat-catcher than the iron billets of the continuous system, because its disadvantages of low conductivity and low specific heat probably outweigh its advantages of roughness and porosity.

99Miscellaneous Effects of Magnetization: Electric Conductivity - Hall Effect - Electro-Thermal Relations - Thermoelectric Quality - Elasticity - Chemical and Voltaic Effects.

85In 1846 he began experiments on the temperature of the earth at different depths and in different soils near Edinburgh, which yielded determinations of the thermal conductivity of trap-tufa, sandstone and pure loose sand.

88When a pure metal is cooled to a very low temperature its electrical conductivity is greatly increased, but this is not the case with an alloy.

89The conductivity for heat (Wiedemann and Franz) or electricity is 8.5, that of silver being taken as loo.

810The equation then becomes a 2 /V = k, or a = A / Vk, so that the molecular conductivity is proportional to the square root of the dilution.

76Abrupt alterations, take place in its density, specific heat, thermo-electric quality, electrical conductivity, temperature-coefficient of electrical resistance, and in some at least of its mechanical properties.

76The conductivity measurements of G.

78Nevertheless, in certain cases, the temperature coefficient of conductivity becomes negative at high temperatures, a solution of phosphoric acid, for example, reaching a maximum conductivity at 75° C.

66Depending on the fact that the electrical conductivity of a metallic conductor is decreased by heat, it consists of two strips of platinum, arranged to form the two arms of a Wheatstone bridge; one strip being exposed to a source of radiation from which the other is shielded, the heat causes a change in the resistance of one arm, the balance of the bridge is destroyed, and a deflection is marked on the galvanometer.

66Dust particles interfere with conduction near the ground, so the relative conductivity in the upper layers may be much greater than that calculated.

67The dimensions of a piece of iron, for example, its elasticity, its thermo-electric power and its electric conductivity are all changed under the influence of magnetism.

67Dust particles interfere with conduction near the ground, so the relative conductivity in the upper layers may be much greater than that calculated.

67The total magnetic induction or flux corresponds to the current of electricity (practically measured in amperes); the induction or flux density B to the density of the current (number of amperes to the square centimetre of section); the magnetic permeability to the specific electric conductivity; and the line integral of the magnetic force, sometimes called the magnetomotive force, to the electro-motive force in the circuit.

53The concentration is known, and the conductivity can be measured experimentally; thus the average velocity with which the ions move past each other under the existent electromotive force can be estimated.

56But the temperature coefficient of conductivity is now generally less than before; thus the effect of temperature on ionization must be of opposite sign to its effect on fluidity.

42Others have arranged a means of obtaining high conductivity wire from cathode-copper without fusion, by depositing the metal in the form of a spiral strip on a cylinder, the strip being subsequently drawn down in the usual way; at present, however, the ordinary methods of wire production are found to be cheaper.

43The rise of conductivity with temperature, therefore, shows that the fluidity becomes greater when the solution is heated.

44Its thermal conductivity is the lowest of all metals, being 18 as compared with silver as 1000; its coefficient of expansion between o° and too° is 0.001341.

44On mixing dilute solutions of the diazonium hydroxide and the alkali together, it is found that the molecular conductivity of the mixture is much less than the sum of the two electrical conductivities of the solutions separately, from which it follows that a portion of the ions present have changed to the non-ionized condition.

44The conductivity, which varies as the product of n into the mobility, will thus vary inversely as the pressure, and so at 36 kilometres will be one hundred times as large as close to the ground.

45The introduction in 1883 of the hard-drawn copper wire of high conductivity invented in 1877 by T.

45The temperature coefficient of conductivity has approximately the same value for most aqueous salt solutions.

45The electric conductivity is given by A.

45The ionization of a solution, then, is usually diminished by raising the temperature, the rise in conductivity being due to the greater increase in fluidity.

33The mercury vapour then possesses a unilateral conductivity, and can be used to filter off all those oscillations in a train which pass in one direction and make them readable on an ordinary galvanometer.

34Distilled water is a very bad conductor, though, even when great care is taken to remove all dissolved bodies, there is evidence to show that some part of the trace of conductivity remaining is due to the water itself.

34Kohlrausch has prepared water of which the conductivity compared with that of mercury was only o 4 oX 11 at 18° C. Even here some little impurity was present, and the conductivity of chemically pure water was estimated by thermodynamic reasoning as o 36X1011 at 18° C. As we shall see later, the conductivity of very dilute salt solutions is proportional to the concentration, so that it is probable that, in most cases, practically all the current is carried by the salt.

34The salts tabulated are those of which the equivalent conductivity reaches a limiting value indicating that complete ionization is reached as dilution is increased.

34If µ be the molecular conductivity, and its value at infinite dilution, the fractional number of molecules dissociated is k /µop, which we may write as a.

34a V(I - a) This constant k gives a numerical value for the chemical affinity, and the equation should represent the effect of dilution on the molecular conductivity of binary electrolytes.

34The influence of temperature on the conductivity of solutions depends on (I) the ionization, and (2) the frictional resistance of the liquid to the passage of the ions, the reciprocal of which is called the ionic fluidity.

35The influence of temperature on the conductivity of solutions depends on (I) the ionization, and (2) the frictional resistance of the liquid to the passage of the ions, the reciprocal of which is called the ionic fluidity.

35Fleming discovered that if the filament is made incandescent by the current from an insulated battery there is a unilateral conductivity of the rarefied gas between the hot filament and the metal plate, such that if the negative terminal of the filament is connected outside the lamp through a coil in which electric oscillations are created with the platinum plate, only one half of the oscillations are permitted to pass, viz., those which carry negative electricity from the hot filament to the cooled plate through the vacuous space.

385.08 At the concentration used by Loomis the electrical conductivity indicates that the ionization is not complete, particularly in the case of the salts with divalent ions in the second list.

23An interesting relation appears when the electrolytic conductivity of solutions is compared with their chemical activity.

23A better basis of comparison would be the ratio of the actual to the limiting conductivity, but since the conductivity of acids is chiefly due to the mobility of the hydrogen ions, its limiting value is nearly the same for all, and the general result of the comparison would be unchanged.

23From these numbers we can, by help of the equation, calculate the conductivity of the acids for any dilution.

23Its electrical conductivity, determined on 99.6% metal, is 60.5% that of copper for equal volumes, or double that of copper for equal weights, and when chemically pure it exhibits a somewhat higher relative efficiency.

23A better basis of comparison would be the ratio of the actual to the limiting conductivity, but since the conductivity of acids is chiefly due to the mobility of the hydrogen ions, its limiting value is nearly the same for all, and the general result of the comparison would be unchanged.

23For example, the physicist determines the density, elasticity, hardness, electrical and thermal conductivity, thermal expansion, &c.; the chemist, on the other hand, investigates changes in composition, such as may be effected by an electric current, by heat, or when two or more substances are mixed.

24It is evident that any other property can be represented by similar diagrams. For example, we can construct the curve of conductivity of alloys of two metals or the surface of conductivity of ternary alloys, and so on for any measurable property.

24The electrical conductivity of a metal is often very much decreased by alloying with it even small quantities of another metal.

24The thermal conductivity also diminishes as salinity increases, the conductivity for heat of sea-water of 35 per mille salinity being 4.2% less than that of pure water.

24Maxwell had himself, at an early stage of his theory, tested the absorbing power of gold-leaf for light, and found that the effective conductivity for luminous vibrations must be very much greater than its steady ohmic value; it is, in fact, there a case of incipient conductivity, which is continually being undone on account of the rapid alternation of force before it is fully established.

24Its electrical conductivity is approximately 1.2, silver at 0° being taken as 100; it is the most diamagnetic substance known, and its thermoelectric properties render it especially valuable for the construction of thermopiles.

25Assuming the materials to be of equal tensile strength per unit of area - hard-drawn copper is stronger, but has a lower conductivity - the adoption of aluminium thus leads to a reduction of 52% in the weight, a gain of 60% in the strength, and an increase of 26% in the diameter of the conductor.

12These are cementite, a definite iron carbide, Fe 3 C, harder than glass and nearly as brittle, but probably very strong under gradually and axially applied stress; and ferrite, pure or nearly pure metallic a-iron, soft, weak, with high electric conductivity, and in general like copper except in colour.

12Determinations of the electrical conductivity of the diazonium chloride and nitrate also show that the diazonium radical is strictly comparable with other quaternary ammonium ions.

12For efficiency the operation must be conducted with small quantities; caking may be prevented by mixing the substance with sand or powdered pumice, or, better, with iron filings, which also renders the decomposition more regular by increasing the conductivity of the mass.

13Conduction has practically no effect, for the coefficient of thermal conductivity in sea-water is so small that if a mass of sea-water were cooled to 0° C. and the surface kept at a temperature of 30° C., 6 months would elapse before a temperature of 15° C. was reached at the depth of 1 3 metres, 1 year at 1 85 metres, and io years at 5.8 metres.

13On setting the dynamo in operation, a current passes through the shunt coil of the ohmmeter proportional to the voltage of the dynamo, and, if there is any sensible leakage through the insulator to earth, at the same time another current passes through the series coil proportional to the conductivity of the insulation of the wiring under the electromotive force used.

13Duncan (M`Gill College Reports, 1899), using the simple method under King's supervision, found the conductivity of very pure copper to be 1.007 for a temperature of 33° C.

00Moreover, the variation of thermal conductivity with temperature is small and uncertain, whereas the variation of electrical conductivity is large and can be accurately determined, and may therefore be legitimately utilized for eliminating the external heat-loss.

00From a comparison of this work with that of Lorenz, it is evident that the values of the conductivity vary widely with the purity of the material, and cannot be safely applied to other specimens than those for which they were found.

00Conductivity and viscosity in a gas should vary in a similar manner since each depends on diffusion in a similar way.

00By similar reasoning the thermal conductivity of a gas should be independent of the density.

00The question of the variation of conductivity with temperature is more difficult.

00If the effects depended merely on the velocity of translation of the molecules, both conductivity and viscosity should increase directly as the square root of the absolute temperature; but the mean free path also varies in a manner which cannot be predicted by theory and which appears to be different for different gases (Rayleigh, Proc. R.S., January 1896).

00The conductivity probably changes with temperature in the same way, being proportional to the product of the viscosity and the specific heat; but the experimental investigation presents difficulties on account of the necessity of eliminating the effects of radiation and convection, and the results of different observers often differ considerably from theory and from each other.

00The values found for the conductivity of air at o° C. range from 000048 to.

00The conductivity of liquids has been investigated by similar methods, generally variations of the thin plate or guard-ring method.

00A determination of the conductivity of water by S.

00It appears probable that the conductivity of a liquid increases considerably with rise of temperature, although the contrary would appear from the work of Lees.

00Among the properties of the neuron is conductivity in all directions.

00Thus, applied to a potential, it gives the direction and magnitude of the force; to a distribution of temperature in a conducting solid, it gives (when multiplied by the conductivity) the flux of heat, &c.

00p. 631) showed how to calculate the effective number of molecules n" = (1 +ek/ko)n,from the molecular conductivity k of the solution and its value ko at infinite dilution, for an electrolyte giving rise to e +I ions.

00A third great use of the electroscope is therefore to detect electric conductivity either in the air or in any other body.

00condenser plate P attached to the outer case, then this substance bestows conductivity on the air between the plates P and P', and the charge of the electroscope begins to leak away.

00He made many measurements of the electric conductivity of different solids and liquids, by comparing the intensity of the electric shock taken through his body and various conductors.

00de C. du Fay on the conductivity of some bodies for the electric agency and the dual character of electrification gave rise to the first notions of ., electricity as an imponderable fluid, or non-gravitative subtile matter, of a more refined and penetrating kind than ordinary liquids and gases.

00He discovered that they had the power of affecting the electric conductivity of materials when in a state of powder, the majority of metallic filings increasing in conductivity.

00In electric conductivity it stands next to silver; the conducting power of silver being equal to loo, that of perfectly pure copper is given by A.

00To-day, by reason of other uses to which electricity is applied, electrically deposited copper of high conductivity is in everincreasing demand, and commands a higher price than copper refined by fusion.

00Such an irregular distribution of the bath, with strong copper sulphate solution from the anode at the bottom and acid solution from the cathode at the top, not only alters the conductivity in different strata and so causes irregular current-distribution, but may lead to the current-density in the upper layers being too great for the proportion of copper there present.

00Its thermal conductivity is, according to Wiedemann and Franz, superior to that of other metals, being in the ratio of ioo: 74 as compared with copper and loo: J4 with gold; it is the most perfect conductor of electricity, standing to copper in the ratio ioo: 75, and to gold I oo: 73.

00He was specially noted for his discovery of the electrical conductivity of bismuth and other metals, and for his pioneer work in wireless telegraphy.

00Another discussed conduction in curved sheets; a third the distribution of electricity in two influencing spheres; a fourth the deter mination of the constant on which depends the intensity of induced currents; while others were devoted to Ohm's law, the motion of electricity in submarine cables, induced magnetism, &c. In other papers, again, various miscellaneous topics were treated - the thermal conductivity of iron, crystalline reflection and refraction, certain propositions in the thermodynamics of solution and vaporization, &c. An important part of his work was contained in his Vorlesungen fiber mathematische Physik (1876), in which the principles of dynamics, as well as various special problems, were treated in a somewhat novel and original manner.

00Hydrobromic acid is one of the "strong" acids, being ionized to a very large extent even in concentrated solution, as shown by the molecular conductivity increasing by only a small amount over a wide range offdilution.

00The former investigates essentially general properties, such as the weight and density, the relation between pressure, volume and temperature (piezometric and thermometric properties), calorimetric properties, diffusion, viscosity, electrical and thermal conductivity, &c., and generally properties independent of composition.

00His later researches included observations on the conductivity of various substances for heat, and on the effect of pressure on the temperature of fusion of different bodies.

00The basis of Fourier's work was his clear conception and definition of conductivity.

00Subsequent experiments led him to doubt this conclusion as regards conductivity, but his thermoelectric experiments (Proc. R.

00dE= - akr dT = - OdT, in each element, where k is the thermal conductivity and ?

00Thermal Conductivity.

00Thomson, on the other hand, set to work to overcome the difficulty by improvement in the manufacture of cables, and first of all in the production of copper of high conductivity and the construction of apparatus which would readily respond to the slightest variation of the current in the cable.

00In this way the metal, owing to its high conductivity and low specific heat as compared to that of water, is kept at a temperature far below its melting point if the water is renewed quickly enough.

00The white storage elements consist of a highly heat resistant material based on special fused alumina which has very high heat capacity and conductivity.

00anisotropic thermal conductivity of quartz.

00Barriers with a low hydraulic conductivity can be produced by adding bentonite to a locally available soil.

00bismuth oxides which exhibit exceptionally high oxide ion conductivity at low temperatures.

00collet clamp type and also coated with laboratory grade Silver for an exemplary finish and excellent conductivity.

00conductivity of polymer melts.

00conductivity of any liquid.

00conductivity of metals in the quantum mechanical approach.

00conductivity of the soil.

00You could measure conductivity of your PEG solution to get a clue how much ionic stuff is present.

00The measurement of thermal diffusivity by laser flash is an alternative way of determining the thermal conductivity of liquid alloys.

00Water has the highest thermal conductivity of any liquid.

00These results could re-open the discussion on the mechanism of ionic conductivity in these materials.

00Void filling should obviously link with changes in the soil's hydraulic conductivity.

00Explain how band theory can account for the electrical conductivity of the elements in groups I - IV.

00We will now revisit the anisotropic thermal conductivity of quartz.

00The low conductivity of char will cause a steep thermal gradient across the char layer.

00conductivity meters accuracy.

00conductivity copper is very readily worked hot or cold.

00conductivity measurement.

00conductivity sensor features an automatic temperature compensated electrode, encapsulated in an impact-resistant epoxy body.

00It is clear, however, that the flow is severely perturbed by the enhanced ionospheric conductivity caused by particle precipitation into the E-region.

00The process of lapping makes the heatsink base smooth to a near mirror finish, which improves heat conductivity.

00Other Methods These, such as soil conductivity meters, metal detectors and micro gravity, exist but will not be discussed here.

00Influence of the environment on the surface conductivity of chemical vapor deposition diamond.

00High conductivity copper is the most common form of the metal available.

00Influence of the environment on the surface conductivity of chemical vapor deposition diamond.

00earth's magnetosphere A fundamental property of space plasmas is that they are collisionless, and as such have extremely high conductivity.

00hydraulic conductivity.

00A similar model was proposed with hydroxyl ions hydrogen bonding to surface H causing polarization and conductivity.

00insulator material made of 95% aluminum oxide - good thermal conductivity and stronger.

00ionic conductivity in these materials.

00Rev. B 60, 6215 (1999 ): Colossal magneto-optical conductivity in doped manganites.

00measurements of the thermal conductivity.

00phosphorous atoms are commonly added to parts of the silicon to increase conductivity.

00reciprocal of conductivity ).

00Furthermore, the conductivity was found to be sensitive to small changes in the composition, a property characteristic of doped semiconductors.

00The exact mix ratio was found to be of vital importance when balancing good conductivity against low shrinkage.

00The high thermal conductivity of the pan acts to rapidly thaw most items.

00thermal conductivity, hot water does not hold its temperatures for very long.

00The above series of salts show striking differences in their behaviour towards reagents; thus, aqueous solutions of the luteo chlorides are strongly ionized, as is shown by their high electric conductivity; and all their chlorine is precipitated on the addition of silver nitrate solution.

00The purpureo chloride has only two-thirds of its chlorine precipitated on the addition of silver nitrate, and the electric conductivity is much less than that of the luteo chloride; again in the praseosalts only one-third of the chlorine is precipitated by silver nitrate, the conductivity again falling; while in the triammine salts all ionization has disappeared.

00The conductivity, which varies as the product of n into the mobility, will thus vary inversely as the pressure, and so at 36 kilometres will be one hundred times as large as close to the ground.

00His data for the thermal conductivity of various metals were for long the most trustworthy at the disposal of physicists, and his determination of the ohm in terms of the specific resistance of mercury showed remarkable skill in quantitative research.

00p. 1351) found that cryoscopic and electric conductivity measurements showed sodium fulminate to be NaCNO.

00The fifth type of wave detector depends upon the peculiar property of rarefied gases or vapours which under some circumstances possess a unilateral conductivity.

00Fleming discovered that if the filament is made incandescent by the current from an insulated battery there is a unilateral conductivity of the rarefied gas between the hot filament and the metal plate, such that if the negative terminal of the filament is connected outside the lamp through a coil in which electric oscillations are created with the platinum plate, only one half of the oscillations are permitted to pass, viz., those which carry negative electricity from the hot filament to the cooled plate through the vacuous space.

00The mercury vapour then possesses a unilateral conductivity, and can be used to filter off all those oscillations in a train which pass in one direction and make them readable on an ordinary galvanometer.

00In addition to the above gaseous rectifiers of oscillations it has been found that several crystals, such as carborundum (carbide of silicon), hessite, anastase and many others possess a unilateral conductivity and enable us to rectify trains of oscillations into continuous currents which can affect a telephone.

00The introduction in 1883 of the hard-drawn copper wire of high conductivity invented in 1877 by T.

00The conductivity measurements of G.

00For example, the physicist determines the density, elasticity, hardness, electrical and thermal conductivity, thermal expansion, &c.; the chemist, on the other hand, investigates changes in composition, such as may be effected by an electric current, by heat, or when two or more substances are mixed.

00when exposed to the action of light its electric conductivity increases.

00Distilled water is a very bad conductor, though, even when great care is taken to remove all dissolved bodies, there is evidence to show that some part of the trace of conductivity remaining is due to the water itself.

00Kohlrausch has prepared water of which the conductivity compared with that of mercury was only o 4 oX 11 at 18Ã‚° C. Even here some little impurity was present, and the conductivity of chemically pure water was estimated by thermodynamic reasoning as o 36X1011 at 18Ã‚° C. As we shall see later, the conductivity of very dilute salt solutions is proportional to the concentration, so that it is probable that, in most cases, practically all the current is carried by the salt.

00If we eliminate the polarization at the electrodes, it can be shown that an electrolyte possesses a definite electric resistance and therefore a definite conductivity.

00The conductivity gives us the amount of electricity conveyed per second under a definite electromotive force.

00The concentration is known, and the conductivity can be measured experimentally; thus the average velocity with which the ions move past each other under the existent electromotive force can be estimated.

00The salts tabulated are those of which the equivalent conductivity reaches a limiting value indicating that complete ionization is reached as dilution is increased.

005.08 At the concentration used by Loomis the electrical conductivity indicates that the ionization is not complete, particularly in the case of the salts with divalent ions in the second list.

00It' would be possible for a body in solution to be dissociated into non-electrical parts, which would give osmotic pressure effects twice or three times the normal value, but, being uncharged, would not act as ions and impart electrical conductivity to the solution.

00But not only has it explained satisfactorily the electrical properties of solutions, but it seems to be the only known hypothesis which is consistent with the experimental relation between the concentration of a solution and its electrical conductivity (see Electric conduction, Brit.

00An interesting relation appears when the electrolytic conductivity of solutions is compared with their chemical activity.

00Nevertheless, the remarkable general agreement of the numbers in the four columns is quite enough to show the intimate connexion between chemical activity and electrical conductivity.

00We may take it, then, that only that portion of these bodies is chemically active which is electrolytically active - that ionization is necessary for such chemical activity as we are dealing with here, just as it is necessary for electrolytic conductivity.

00If µ be the molecular conductivity, and its value at infinite dilution, the fractional number of molecules dissociated is k /µop, which we may write as a.

00a V(I - a) This constant k gives a numerical value for the chemical affinity, and the equation should represent the effect of dilution on the molecular conductivity of binary electrolytes.

00The equation then becomes a 2 /V = k, or a = A / Vk, so that the molecular conductivity is proportional to the square root of the dilution.

00From these numbers we can, by help of the equation, calculate the conductivity of the acids for any dilution.

00The temperature coefficient of conductivity has approximately the same value for most aqueous salt solutions.

00The rise of conductivity with temperature, therefore, shows that the fluidity becomes greater when the solution is heated.

00But the temperature coefficient of conductivity is now generally less than before; thus the effect of temperature on ionization must be of opposite sign to its effect on fluidity.

00The ionization of a solution, then, is usually diminished by raising the temperature, the rise in conductivity being due to the greater increase in fluidity.

00Nevertheless, in certain cases, the temperature coefficient of conductivity becomes negative at high temperatures, a solution of phosphoric acid, for example, reaching a maximum conductivity at 75Ã‚° C.

00For example, a rise in temperature of the bath causes an increase in its conductivity, so that a lower E.M.F.

00Others have arranged a means of obtaining high conductivity wire from cathode-copper without fusion, by depositing the metal in the form of a spiral strip on a cylinder, the strip being subsequently drawn down in the usual way; at present, however, the ordinary methods of wire production are found to be cheaper.

00The conductivity for heat (Wiedemann and Franz) or electricity is 8.5, that of silver being taken as loo.

00Miscellaneous Effects of Magnetization: Electric Conductivity - Hall Effect - Electro-Thermal Relations - Thermoelectric Quality - Elasticity - Chemical and Voltaic Effects.

00The dimensions of a piece of iron, for example, its elasticity, its thermo-electric power and its electric conductivity are all changed under the influence of magnetism.

00The total magnetic induction or flux corresponds to the current of electricity (practically measured in amperes); the induction or flux density B to the density of the current (number of amperes to the square centimetre of section); the magnetic permeability to the specific electric conductivity; and the line integral of the magnetic force, sometimes called the magnetomotive force, to the electro-motive force in the circuit.

00The principal points of difference are that (I) the magnetic permeability, unlike the electric conductivity, which is independent of the strength of the current, is not in general constant; (2) there is no perfect insulator for magnetic induction, which will pass more or less freely through all known substances.

00Abrupt alterations, take place in its density, specific heat, thermo-electric quality, electrical conductivity, temperature-coefficient of electrical resistance, and in some at least of its mechanical properties.

00Longitudinal change of electric conductivity.

00thermal conductivity.

00For data concerning the conductivity of the organic bases see G.

00In 1846 he began experiments on the temperature of the earth at different depths and in different soils near Edinburgh, which yielded determinations of the thermal conductivity of trap-tufa, sandstone and pure loose sand.

00Towards the end of his life he was occupied with experimental inquiries into the laws of the conduction of heat in bars, and his last piece of work was to show that the thermal conductivity of iron diminishes with increase of temperature.

00For efficiency the operation must be conducted with small quantities; caking may be prevented by mixing the substance with sand or powdered pumice, or, better, with iron filings, which also renders the decomposition more regular by increasing the conductivity of the mass.

00Depending on the fact that the electrical conductivity of a metallic conductor is decreased by heat, it consists of two strips of platinum, arranged to form the two arms of a Wheatstone bridge; one strip being exposed to a source of radiation from which the other is shielded, the heat causes a change in the resistance of one arm, the balance of the bridge is destroyed, and a deflection is marked on the galvanometer.

00It is evident that any other property can be represented by similar diagrams. For example, we can construct the curve of conductivity of alloys of two metals or the surface of conductivity of ternary alloys, and so on for any measurable property.

00The electrical conductivity of a metal is often very much decreased by alloying with it even small quantities of another metal.

00When a pure metal is cooled to a very low temperature its electrical conductivity is greatly increased, but this is not the case with an alloy.

00The electric conductivity is given by A.

00Its conductivity for heat has been variously given as 103 (C. M.

00Its thermal conductivity is the lowest of all metals, being 18 as compared with silver as 1000; its coefficient of expansion between oÃ‚° and tooÃ‚° is 0.001341.

00Its electrical conductivity is approximately 1.2, silver at 0Ã‚° being taken as 100; it is the most diamagnetic substance known, and its thermoelectric properties render it especially valuable for the construction of thermopiles.

00When present in other metals, even in very small quantity, bismuth renders them brittle and impairs their electrical conductivity.

00The thermal conductivity also diminishes as salinity increases, the conductivity for heat of sea-water of 35 per mille salinity being 4.2% less than that of pure water.

00The electrical conductivity of sea-water increases with the salinity; at 59Ã‚° F.

00Conduction has practically no effect, for the coefficient of thermal conductivity in sea-water is so small that if a mass of sea-water were cooled to 0Ã‚° C. and the surface kept at a temperature of 30Ã‚° C., 6 months would elapse before a temperature of 15Ã‚° C. was reached at the depth of 1 3 metres, 1 year at 1 85 metres, and io years at 5.8 metres.

00On setting the dynamo in operation, a current passes through the shunt coil of the ohmmeter proportional to the voltage of the dynamo, and, if there is any sensible leakage through the insulator to earth, at the same time another current passes through the series coil proportional to the conductivity of the insulation of the wiring under the electromotive force used.

00Maxwell had himself, at an early stage of his theory, tested the absorbing power of gold-leaf for light, and found that the effective conductivity for luminous vibrations must be very much greater than its steady ohmic value; it is, in fact, there a case of incipient conductivity, which is continually being undone on account of the rapid alternation of force before it is fully established.

00It is a very weak monobasic acid, and the aqueous solution has a very low electric conductivity.

00Charcoal is valuable for its infusibility and low conductivity for heat (allowing substances to be strongly heated upon it), and for its powerful reducing properties; so that it is chiefly employed in testing the fusibility of minerals and in reduction.

00Its electrical conductivity, determined on 99.6% metal, is 60.5% that of copper for equal volumes, or double that of copper for equal weights, and when chemically pure it exhibits a somewhat higher relative efficiency.

00Assuming the materials to be of equal tensile strength per unit of area - hard-drawn copper is stronger, but has a lower conductivity - the adoption of aluminium thus leads to a reduction of 52% in the weight, a gain of 60% in the strength, and an increase of 26% in the diameter of the conductor.

00These are cementite, a definite iron carbide, Fe 3 C, harder than glass and nearly as brittle, but probably very strong under gradually and axially applied stress; and ferrite, pure or nearly pure metallic a-iron, soft, weak, with high electric conductivity, and in general like copper except in colour.

0019; but this would probably recover less heat than the continuous system, first, because it transfers the heat from flame to metal indirectly instead of directly; and, second, because the brickwork of the Siemens system is probably a poorer heat-catcher than the iron billets of the continuous system, because its disadvantages of low conductivity and low specific heat probably outweigh its advantages of roughness and porosity.

00Determinations of the electrical conductivity of the diazonium chloride and nitrate also show that the diazonium radical is strictly comparable with other quaternary ammonium ions.

00On mixing dilute solutions of the diazonium hydroxide and the alkali together, it is found that the molecular conductivity of the mixture is much less than the sum of the two electrical conductivities of the solutions separately, from which it follows that a portion of the ions present have changed to the non-ionized condition.

00But later experimental researches have shown that the simple assumption of constant coefficients of conductivity and emissivity, on which the mathematical theory is based, is in many respects inadequate, and the special mathematical methods developed by J.

00The high conductivity of metals is then explained by the small mass and high velocity of diffusion of these electric atoms. Assuming the kinetic energy of an electric atom at any temperature to be equal to that of a gaseous molecule, its velocity, on Sir J.

00The thermal conductivity of the substance is the constant ratio of the rate of transmission to the temperature gradient.

00To take the simple case of the " wall " or flat plate considered by Fourier for the definition of thermal conductivity, suppose that a quantity of heat Q passes in the time T through an area A of a plate of conductivity k and thickness x, the sides of which are constantly maintained at temperatures B' and 8".

00In the steady state, the product kdO/dx must be constant, or the gradient must vary inversely as the conductivity, if the latter is a function of 0 or x.

00The corresponding gradient is of the order of zÃ‚° C. in ioo ft., but varies inversely with the conductivity of the strata at different depths.

00If Q is expressed in terms of this unit in equation (I), it is necessary to divide by c, or to replace k on the right-hand side by the ratio k/c. This ratio determines the rate of diffusion of temperature, and is called the thermometric conductivity or, more shortly, the diffusivity.

00The velocity of propagation of temperature waves will be the same under similar conditions in two substances which possess the same diffusivity, although they may differ in conductivity.

00This he called the external conductivity, but the term emissivity is more convenient.

00- Measurements of thermal conductivity present peculiar difficulties on account of the variety of quantities to be observed, the slowness of the process of conduction, the impossibility of isolating a quantity of heat, and the difficulty of exactly realizing the theoretical conditions of the problem.

00To find the conductivity, it is necessary to measure all the quantities which occur in equation (I) to a similar order of accuracy.

00This gives very good contact, and the conductivity of the metal being more than loo times that of the crystal, the temperature of the surface is determinate.

00In applying the plate method to the determination of the conductivity of iron, E.

00This gives an average value of the conductivity over the range, but it is better to observe the temperatures at three distances, and to assume k to be a linear function of the temperature, in which case the solution of the equation is still very simple, namely, 0+Ze6 2 =a log r+b, (3) where e is the temperature-coefficient of the conductivity.

00For these reasons the temperature-coefficient of the conductivity could not be determined satisfactorily on this particular form of apparatus, but the mean results were probably trustworthy to I or 2%.

00The method of Forbes (in which the conductivity is deduced from the steady distribution of temperature on the assumption that the rate of loss of heat at each point of the bar is the same as that observed in an auxiliary experiment in which a short bar of the same kind is set to cool under conditions which are supposed to be identical) is well known, but a consideration of its weak points is very instructive, and the results have been most remarkably misunderstood and misquoted.

00This is not very surprising, if the values in the following table are compared :- Conductivity of Forbes's Iron Bar D - (1 25 inches square).

00The results of Forbes are interesting historically as having been the first approximately correct determinations of conductivity in absolute value.

00The bar was a special sample of cast-iron, the conductivity of which was required for some experiments on the condensation of steam (Proc. Inst.

00p. 503, 1888) applied this method directly to mercury, and determined the conductivity of some other metals by comparison with mercury.

00No calorimetric observations are required, but the results are obtained in terms of the thermal capacity of unit volume c, and the measurements give the diffusivity klc, instead of the calorimetric conductivity k.

00The quantity of heat absorbed by the stratum (x' x") in the interval considered can also be expressed in terms of the calorimetric conductivity k.

00It is probable for this reason that the average conductivity of the earth's crust, as deduced from surface observations, is too large; and that estimates of the age of the earth based on such measurements are too low, and require to be raised; they would thereby be brought into better agreement with the conclusions of geologists derived from other lines of argument.

00The heat per second gained by conduction by an element dx of the bar, of conductivity k and cross section q, at a point where the gradient is dB/dx, may be written gk(d 2 6/dx 2)dx.

00Angstrom endeavoured to find the variation of conductivity by this method, but he assumed c to be the same for two different bars, and made no allowance for its variation with temperature.

00He thus found nearly the same rate of variation for the thermal as for the electric conductivity.

00The thermal conductivity was determined in the neighbourhood of 20Ã‚° C. with a water jacket, and near I IoÃ‚° C. by the use of a steam jacket.

00The conductivity of the same bars was independently determined by the method of Forbes, employing an ingenious formula for the heat-loss in place of Newton's law.

00The thermal capacity and electrical conductivity were measured at various temperatures on the same specimens of metal.

00One important result, which might be regarded as established by this work, was that the ratio k/k of the thermal to the electrical conductivity, though nearly constant for the good conductors at any one temperature such as 0Ã‚° C., increased with rise of temperature nearly in proportion to the absolute temperature.

00are two electrical methods which have been recently applied to the measurement of the conductivity of metals, (a) the resistance method, devised by Callendar, and applied by him, and also by R.

00In this case the curve representing the distribution of temperature is a parabola, and the conductivity k is deduced from the mean rise of temperature (R-RÃ‚°)/aRÃ‚° by observing the increase of resistance R-RÃ‚° of the bar, and the current C. It is also necessary to measure the cross-section g, the length 1, and the temperature-coefficient a for the range of the experiment.

00(9) By a property of the parabola, the mean temperature is 3rds of the maximum temperature, we have therefore (R - R 0)/aRo =1C 2 Ra/12gk, (io) which gives the conductivity directly in terms of the quantities actually observed.

00In addition to the simple measurements of the conductivity (M`Gill College, 18 951896), some very elaborate experiments were made by King (Proc. Amer.

00Duncan (M`Gill College Reports, 1899), using the simple method under King's supervision, found the conductivity of very pure copper to be 1.007 for a temperature of 33Ã‚° C.

00Moreover, the variation of thermal conductivity with temperature is small and uncertain, whereas the variation of electrical conductivity is large and can be accurately determined, and may therefore be legitimately utilized for eliminating the external heat-loss.

00From a comparison of this work with that of Lorenz, it is evident that the values of the conductivity vary widely with the purity of the material, and cannot be safely applied to other specimens than those for which they were found.

00Conductivity and viscosity in a gas should vary in a similar manner since each depends on diffusion in a similar way.

00By similar reasoning the thermal conductivity of a gas should be independent of the density.

00The question of the variation of conductivity with temperature is more difficult.

00If the effects depended merely on the velocity of translation of the molecules, both conductivity and viscosity should increase directly as the square root of the absolute temperature; but the mean free path also varies in a manner which cannot be predicted by theory and which appears to be different for different gases (Rayleigh, Proc. R.S., January 1896).

00The conductivity probably changes with temperature in the same way, being proportional to the product of the viscosity and the specific heat; but the experimental investigation presents difficulties on account of the necessity of eliminating the effects of radiation and convection, and the results of different observers often differ considerably from theory and from each other.

00The values found for the conductivity of air at oÃ‚° C. range from 000048 to.

00The conductivity of liquids has been investigated by similar methods, generally variations of the thin plate or guard-ring method.

00A determination of the conductivity of water by S.

00It appears probable that the conductivity of a liquid increases considerably with rise of temperature, although the contrary would appear from the work of Lees.

00Among the properties of the neuron is conductivity in all directions.

00Thus, applied to a potential, it gives the direction and magnitude of the force; to a distribution of temperature in a conducting solid, it gives (when multiplied by the conductivity) the flux of heat, &c.

00p. 631) showed how to calculate the effective number of molecules n" = (1 +ek/ko)n,from the molecular conductivity k of the solution and its value ko at infinite dilution, for an electrolyte giving rise to e +I ions.

00A third great use of the electroscope is therefore to detect electric conductivity either in the air or in any other body.

00condenser plate P attached to the outer case, then this substance bestows conductivity on the air between the plates P and P', and the charge of the electroscope begins to leak away.

00He made many measurements of the electric conductivity of different solids and liquids, by comparing the intensity of the electric shock taken through his body and various conductors.

00de C. du Fay on the conductivity of some bodies for the electric agency and the dual character of electrification gave rise to the first notions of ., electricity as an imponderable fluid, or non-gravitative subtile matter, of a more refined and penetrating kind than ordinary liquids and gases.

00He discovered that they had the power of affecting the electric conductivity of materials when in a state of powder, the majority of metallic filings increasing in conductivity.

00In electric conductivity it stands next to silver; the conducting power of silver being equal to loo, that of perfectly pure copper is given by A.

00To-day, by reason of other uses to which electricity is applied, electrically deposited copper of high conductivity is in everincreasing demand, and commands a higher price than copper refined by fusion.

00Such an irregular distribution of the bath, with strong copper sulphate solution from the anode at the bottom and acid solution from the cathode at the top, not only alters the conductivity in different strata and so causes irregular current-distribution, but may lead to the current-density in the upper layers being too great for the proportion of copper there present.

00Its thermal conductivity is, according to Wiedemann and Franz, superior to that of other metals, being in the ratio of ioo: 74 as compared with copper and loo: J4 with gold; it is the most perfect conductor of electricity, standing to copper in the ratio ioo: 75, and to gold I oo: 73.

00He was specially noted for his discovery of the electrical conductivity of bismuth and other metals, and for his pioneer work in wireless telegraphy.

00Another discussed conduction in curved sheets; a third the distribution of electricity in two influencing spheres; a fourth the deter mination of the constant on which depends the intensity of induced currents; while others were devoted to Ohm's law, the motion of electricity in submarine cables, induced magnetism, &c. In other papers, again, various miscellaneous topics were treated - the thermal conductivity of iron, crystalline reflection and refraction, certain propositions in the thermodynamics of solution and vaporization, &c. An important part of his work was contained in his Vorlesungen fiber mathematische Physik (1876), in which the principles of dynamics, as well as various special problems, were treated in a somewhat novel and original manner.

00Metallic selenium is a conductor of electricity, and its conductivity is increased by light; this property has been utilized in apparatus for transmitting photographs by telegraphy (see Telegraph).

00Hydrobromic acid is one of the "strong" acids, being ionized to a very large extent even in concentrated solution, as shown by the molecular conductivity increasing by only a small amount over a wide range offdilution.

00The former investigates essentially general properties, such as the weight and density, the relation between pressure, volume and temperature (piezometric and thermometric properties), calorimetric properties, diffusion, viscosity, electrical and thermal conductivity, &c., and generally properties independent of composition.

00His later researches included observations on the conductivity of various substances for heat, and on the effect of pressure on the temperature of fusion of different bodies.

00The basis of Fourier's work was his clear conception and definition of conductivity.

00Subsequent experiments led him to doubt this conclusion as regards conductivity, but his thermoelectric experiments (Proc. R.

00dE= - akr dT = - OdT, in each element, where k is the thermal conductivity and ?

00Thomson, on the other hand, set to work to overcome the difficulty by improvement in the manufacture of cables, and first of all in the production of copper of high conductivity and the construction of apparatus which would readily respond to the slightest variation of the current in the cable.

00In this way the metal, owing to its high conductivity and low specific heat as compared to that of water, is kept at a temperature far below its melting point if the water is renewed quickly enough.

00In the case of electrical conductivity, the data are input and output as resistivity (reciprocal of conductivity).

00The metal surface needs to be high conductivity to limit the resistive loss.

00Furthermore, the conductivity was found to be sensitive to small changes in the composition, a property characteristic of doped semiconductors.

00The exact mix ratio was found to be of vital importance when balancing good conductivity against low shrinkage.

00The high thermal conductivity of the pan acts to rapidly thaw most items.

00In addition, due to cast iron 's high degree of thermal conductivity, hot water does not hold its temperatures for very long.

00You get the benefits of both materials-the heat conductivity of the copper and the lack of reactivity from the stainless steel.

00Aluminum pots are very lightweight and have great conductivity, meaning the heat is quickly transferred throughout the pot.

00Copper pans are best for even heating and have superior conductivity so they work well for high heat cooking like sautéing.

00Conductivity: After frequent use, some cake pans tend to warp or bend.

00Alloys can also affect things like conductivity, making gold alloys valuable in many technical uses.

00Low karat gold can also be used for visual effects and to alter various attributes of the blend such as conductivity.

00The composites made by mixing cork granules and cement have low thermal conductivity, low density and good energy absorption.

00Cubic zirconia also has different heat conductivity, and when measured, will have a red indicator instead of the green that diamonds produce.

00Using a product such as a DeoxIT Pen after the initial cleaning will improve conductivity in addition to cleaning, lubricating and protecting the contacts and connectors.

00To ensure conductivity, you have to apply and replace gel pads against your skin as well.

00If we eliminate the polarization at the electrodes, it can be shown that an electrolyte possesses a definite electric resistance and therefore a definite conductivity.

01It' would be possible for a body in solution to be dissociated into non-electrical parts, which would give osmotic pressure effects twice or three times the normal value, but, being uncharged, would not act as ions and impart electrical conductivity to the solution.

01Nevertheless, the remarkable general agreement of the numbers in the four columns is quite enough to show the intimate connexion between chemical activity and electrical conductivity.

01We may take it, then, that only that portion of these bodies is chemically active which is electrolytically active - that ionization is necessary for such chemical activity as we are dealing with here, just as it is necessary for electrolytic conductivity.

01Longitudinal change of electric conductivity.

01thermal conductivity.

01When present in other metals, even in very small quantity, bismuth renders them brittle and impairs their electrical conductivity.

01It is a very weak monobasic acid, and the aqueous solution has a very low electric conductivity.

01But later experimental researches have shown that the simple assumption of constant coefficients of conductivity and emissivity, on which the mathematical theory is based, is in many respects inadequate, and the special mathematical methods developed by J.

01The high conductivity of metals is then explained by the small mass and high velocity of diffusion of these electric atoms. Assuming the kinetic energy of an electric atom at any temperature to be equal to that of a gaseous molecule, its velocity, on Sir J.

01The thermal conductivity of the substance is the constant ratio of the rate of transmission to the temperature gradient.

01To take the simple case of the " wall " or flat plate considered by Fourier for the definition of thermal conductivity, suppose that a quantity of heat Q passes in the time T through an area A of a plate of conductivity k and thickness x, the sides of which are constantly maintained at temperatures B' and 8".

01In the steady state, the product kdO/dx must be constant, or the gradient must vary inversely as the conductivity, if the latter is a function of 0 or x.

01The corresponding gradient is of the order of z° C. in ioo ft., but varies inversely with the conductivity of the strata at different depths.

01If Q is expressed in terms of this unit in equation (I), it is necessary to divide by c, or to replace k on the right-hand side by the ratio k/c. This ratio determines the rate of diffusion of temperature, and is called the thermometric conductivity or, more shortly, the diffusivity.

01The velocity of propagation of temperature waves will be the same under similar conditions in two substances which possess the same diffusivity, although they may differ in conductivity.

01This he called the external conductivity, but the term emissivity is more convenient.

01- Measurements of thermal conductivity present peculiar difficulties on account of the variety of quantities to be observed, the slowness of the process of conduction, the impossibility of isolating a quantity of heat, and the difficulty of exactly realizing the theoretical conditions of the problem.

01To find the conductivity, it is necessary to measure all the quantities which occur in equation (I) to a similar order of accuracy.

01This gives very good contact, and the conductivity of the metal being more than loo times that of the crystal, the temperature of the surface is determinate.

01In applying the plate method to the determination of the conductivity of iron, E.

01This gives an average value of the conductivity over the range, but it is better to observe the temperatures at three distances, and to assume k to be a linear function of the temperature, in which case the solution of the equation is still very simple, namely, 0+Ze6 2 =a log r+b, (3) where e is the temperature-coefficient of the conductivity.

01For these reasons the temperature-coefficient of the conductivity could not be determined satisfactorily on this particular form of apparatus, but the mean results were probably trustworthy to I or 2%.

01The method of Forbes (in which the conductivity is deduced from the steady distribution of temperature on the assumption that the rate of loss of heat at each point of the bar is the same as that observed in an auxiliary experiment in which a short bar of the same kind is set to cool under conditions which are supposed to be identical) is well known, but a consideration of its weak points is very instructive, and the results have been most remarkably misunderstood and misquoted.

01This is not very surprising, if the values in the following table are compared :- Conductivity of Forbes's Iron Bar D - (1 25 inches square).

01The results of Forbes are interesting historically as having been the first approximately correct determinations of conductivity in absolute value.

01The bar was a special sample of cast-iron, the conductivity of which was required for some experiments on the condensation of steam (Proc. Inst.

01p. 503, 1888) applied this method directly to mercury, and determined the conductivity of some other metals by comparison with mercury.

01No calorimetric observations are required, but the results are obtained in terms of the thermal capacity of unit volume c, and the measurements give the diffusivity klc, instead of the calorimetric conductivity k.

01The quantity of heat absorbed by the stratum (x' x") in the interval considered can also be expressed in terms of the calorimetric conductivity k.

01It is probable for this reason that the average conductivity of the earth's crust, as deduced from surface observations, is too large; and that estimates of the age of the earth based on such measurements are too low, and require to be raised; they would thereby be brought into better agreement with the conclusions of geologists derived from other lines of argument.

01The heat per second gained by conduction by an element dx of the bar, of conductivity k and cross section q, at a point where the gradient is dB/dx, may be written gk(d 2 6/dx 2)dx.

01Angstrom endeavoured to find the variation of conductivity by this method, but he assumed c to be the same for two different bars, and made no allowance for its variation with temperature.

01He thus found nearly the same rate of variation for the thermal as for the electric conductivity.

01The thermal conductivity was determined in the neighbourhood of 20° C. with a water jacket, and near I Io° C. by the use of a steam jacket.

01The conductivity of the same bars was independently determined by the method of Forbes, employing an ingenious formula for the heat-loss in place of Newton's law.

01The thermal capacity and electrical conductivity were measured at various temperatures on the same specimens of metal.

01One important result, which might be regarded as established by this work, was that the ratio k/k of the thermal to the electrical conductivity, though nearly constant for the good conductors at any one temperature such as 0° C., increased with rise of temperature nearly in proportion to the absolute temperature.

01are two electrical methods which have been recently applied to the measurement of the conductivity of metals, (a) the resistance method, devised by Callendar, and applied by him, and also by R.

01In this case the curve representing the distribution of temperature is a parabola, and the conductivity k is deduced from the mean rise of temperature (R-R°)/aR° by observing the increase of resistance R-R° of the bar, and the current C. It is also necessary to measure the cross-section g, the length 1, and the temperature-coefficient a for the range of the experiment.

01(9) By a property of the parabola, the mean temperature is 3rds of the maximum temperature, we have therefore (R - R 0)/aRo =1C 2 Ra/12gk, (io) which gives the conductivity directly in terms of the quantities actually observed.

01In addition to the simple measurements of the conductivity (M`Gill College, 18 951896), some very elaborate experiments were made by King (Proc. Amer.

01

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