Heat, theories material theory

It should be noted that the two explanations of activity for heat treated materials do not necessarily disagree. Some researchers have proposed a combination of the previously discussed theories, in that the more active metal-N4 center can remain intact for treatments between 400-700 °C, but a new more stable site forms with higher temperature treatments.73,79,92,93 In fact, one of the earliest reports of an ORR-active heat treated macrocycle discussed the fact that the optimal treatment temperature was 600 °C, but higher treatments up to 1000 °C created a more stable, though slightly less active catalyst.9... 

In this volume, there is an account of the basic theory underlying the various Unit Operations, and typical items of equipment are described. The equipment items are the essential components of a complete chemical plant, and the way in which such a plant is designed is the subject of Volume 6 of the series which has just appeared. The new volume includes material on flowsheeting, heat and material balances, piping, mechanical construction and costing. It completes the Series and forms an introduction to the very broad subject of Chemical Engineering Design. 

The phenomena of heat require explanation, however, and he expresses himself in favor of the material theory of heat—as an imponderable fluid pervading all space, which condensing in the pores of a substance accounts for the various phenomena of absorption or evolution of heat. The physicists, in fact, were divided for a long time after Lavoisier upon the nature of heat—whether it were a mode of motion or an imponderable fluid. An English writer, Metcalfe, in a two volume work on caloric, 1837, presents the material theory about as strongly as possible. 

Particles suspended in a nonuniform gas may be subject to absorption or loss of heat or material by diffusional transport. If the particle is suspended without motion in a stagnant gas, heat or mass transfer to or from the body can be estimated from heat conduction or diffusion theory. One finds that the net rate of transfer of heat to the particle surface in a gas is... 

In a long note describing his experiments on the variation of the latent heat of steam with temperature, Watt acknowledged that Mr. Southern is inclined to conclude, from the experiments on the latent heat of steam at high temperature [presented in the Appendix]... that the latent heat is a constant quantity, instead of the sum of the latent and sensible heats being so .55 This seems tantamount to an abandonment of what is known as Watt s Taw - that the sum of the latent and sensible heats is a constant. Watt had used this idea not only in his development of expansive working of steam engines but also, as we will see, it was important to his ideas about the chemical transformation of water into air.56 So, to abandon Watt s Law was to jettison a key part of Watt s chemical material theory of heat. We will see shortly, however, that a place was retained for it in a clever fashion. 

In all this, Forbes does not delve at all deeply into just what the theory was that Watt brought into such productive relation to his engineering practice. Vague talk of the theory of heat, of physical principles and the like is all that his readers were offered, and this vagueness allowed for awkward issues such as Watt s commitment to a material theory of heat, let alone a chemical one, to be elided. Many of the grounds on which Watt s chemistry had been judged by Whewell, Harcourt and Forbes himself as outside the bounds of sound philosophical practice were used to rule his engineering practice as within those bounds. The mechanical Watt was awarded the tide philosopher , which the chemical Watt had been denied. 

After Watt moved to Birmingham in 1774 he remained loyal to the Blackian tradition. Thus, for example, in 1779 he reported to Black that he was standing firm against those who challenged him with a non-material theory of heat ... 

Watt, like Black, was committed to one of three major views of heat extant at the time. The first of the three views was that heat was motion, or the vibration of the parts of ordinary material bodies. This mechanical theory of heat had been favoured by Boyle and had been endorsed by Newton. But the mechanical theory was not fashionable in the mid- to late eighteenth century. We know that a mathematical theory of heat as motion was developed by Henry Cavendish in the 1780s but, typically, not published.42 This type of theory was, of course, to become the correct view of heat by the mid-nineteenth century. The second and third accounts of heat are often collapsed together as material theories since in both heat was a special substance rather than the motion of ordinary matter. The distinction between these two material theories is clearly described by McCormmach ... 

Joseph Black subscribed to a version of the first material theory. He considered heat to be a special form of matter that combined with ordinary matter as a result of chemical forces of attraction. The phenomenon of cold produced by evaporation was explained by Black as follows. The cold experienced when water evaporates is the result of the water absorbing sensible heat as the water becomes vapour. The heat is not lost, rather the heat combines chemically with the vapour and it is this that gives the vapour the property of elasticity. Thus water absorbs the matter of heat, which becomes latent (or fixed as Black termed it initially) because it is now chemically combined with the water. Through this combination, the latent heat confers the property of fluidity or elasticity upon the vapour, that is upon the steam. 

This fundamental property of matter must have its origin in the nature of heat itself. The fluid theory of heat assumed that the caloric fluid tended like a gas to distribute itself uniformly over the whole of the available space, and hence to travel from places of higher to places of lower density. The discovery that heat could be converted into mechanical work, and vice versa, led to the abandonment of the material theory of heat and to the acceptance of the kinetic theory, which looks upon heat as the kinetic energy of the ultimate particles of which... 

The reverse process,. e. the production of heat when work is done, was discovered at the beginning of the nineteenth century. The exponents of the material theory of heat, guided by the assumption of the constancy of the heat substance in nature, explained the evolution of heat on turning metals by a supposed decrease in their specific heat. Count Rumford showed, however, by experiments on the large scale that the rise in temperature caused by the boring of a cannon cannot be accounted for by the decrease in the specific heat of the turnings. In 1798 he was the first to state clearly that the motion of the horses, which were used to drive the drill, was the true cause of the observed rise in temperature. 

The phase separation processes discussed in this book involve interactions between vapor and liquid phases, or between two liquid phases, or between a vapor phase and two liquid phases. The thermodynamic principles that govern these interactions are introduced in this chapter. Since this chapter is not intended as a full treatise on thermodynamics, only those aspects of the subject that have a direct bearing on phase separation processes are covered. To this end, theory is developed from the basic principles and carried through to the formulation of practical methods for calculating relevant thermodynamic properties, such as fugacity and enthalpy. These properties are essential for carrying out heat and material balance calculations in the separation processes described in this book. 

It is evident that Geber s quicksilver and sulphur were not the material elements known by those names, for he mentions that on heating the material elements together the red stone known to men of science as cinnabar was produced. The constituents of gold were thus hypothetical or idealised substances to which material quicksilver and sulphur were the nearest known approach (p. 71). The European alchemist, Albertus Magnus, who became Bishop of Ratisbon in 1259, is believed to have subscribed to the quicksilver-sulphur theory, although the authenticity of the alchemistic works attributed to him has been queried. It was he who introduced the word affinity to indicate the reason why sulphur united with quicksilver — a term that is widely used ana appreciated by chemists to-day. 

Currently, there is no theory to forecast the thermal conductivity of the refractory material and its temperature dependence. For heat insulation materials, the value of the thermal conductivity may increase two to five times as the temperature increases from 200 to 1,200... 

Thermal Expansion of Refractory and Heat Insulation Materials Elements of Theory... 

An important approach was introduced by Cleghorn, who in 1779 related the material theory of heat in his book De igne as follows ...since the quantity of fire distributed among bodies increases with the attraction for fire that the bodies exert and decreases with the repulsion between the fire particles themselves, it follows that if in any body the former quantity is diminished or the latter increased, then the fire will flow from that body until equilibrium is again restored. Heat is then said to be generated. On the other hand, if the attraction of any body were to be increased or if the repulsion between the fire particles were diminished, more fire would flow into the body and in this case cold is said to be generated... ... 

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