We generally look for answers with sources, often from historical figures in the field in question. Can you add some in to your answer, and perhaps lengthen in a little? As I have none in this case, I'll delete the answer soon. Your idea has promise. It makes sense. I bet you can find something out there that confirms it.
I'd suggest that you note that you don't yet have a source, but are finding one. Alternatively, though, you could delete this and later undelete it when you have a source. It's up to you. This meta post can give you some ideas of what we're looking for.
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The experiment that showed most directly the connection between mechanical action and heat involved the stirring of water by a paddle.
He gave an extensive summary of this work in a report [ 2 ] to the Royal Society of London in June, In one design, the paddles, immersed in water, were mounted on a vertical shaft, rotated by a cord propelled by falling weights.
The temperature increase of the water was of order one degree centigrade. The experiment required very careful control of the ambient conditions and corrections for extraneous heat flow. The law, based on the idea of the conservation of energy, states that for a process in a defined system, the change in internal energy is equal to the amount of heat absorbed minus the work done. Joule recognized that, in a container that cannot exchange heat with the surroundings, if a gas is compressed, and then allowed to expand into a vacuum, the expanding gas does no work.
Therefore, according to the First Law, the energy of an ideal gas would not change, nor would its temperature. His experiments showed this to be the case. However, small temperature changes do occur that were too small to be detected in his experiments.
This work came to the attention of Lord Kelvin, who joined Joule in a more sensitive experiment involving expansion of the gas through a porous plug. This experiment showed significant temperature changes that depended on the initial temperature and pressure. Later, these changes were understood to be due to the force between molecules.
This was the Joule-Thomson experiment. Active 4 years, 8 months ago. Viewed times. Improve this question. Conifold 5, 1 1 gold badge 17 17 silver badges 29 29 bronze badges. Sir Visto Sir Visto 1 1 bronze badge. One thing I can say to the answer is that when you are doing precise operations, like making cannon bores, you notice the subtle results more because you can't just write off those results as the result of sloppiness. Add a comment. Active Oldest Votes. In the notes on Kirwan's Essay on Phlogiston Lavoisier writes: " when a metal is heated to a certain temperature, and when its particles are separated from each other to a certain distance by heat, and their attraction to each other is sufficiently diminished, it becomes capable of decomposing vital air, from which it seizes the base, namely oxygen, and sets the other principle, namely the caloric, at liberty Improve this answer.
Conifold Conifold 5, 1 1 gold badge 17 17 silver badges 29 29 bronze badges. In his writings Truesdell went so far that for a while he used the word calory in place of entropy. It seems to me he could have come up with the same idea just from a simple thought experiment: "What happens if I rub two blocks together? They'll get hot. If I let them cool down, then rub them together again, what will happen? They'll get hot again He apparently wished to grant water the highest station in human life, and a fluid that could be neither created nor destroyed stood in the way.
Boring cannon measurements at the arsenal in Munich were designed with a particular result in mind. Recent editions of these same books, much heavier and more colorful, have dropped that material in favor of endless detailed instruction on how to solve textbook problems. This may be, in part, a necessary response to less well prepared students, and possibly teachers, but the new texts, despite four color artwork on shiny paper, are rather dreary.
My solution is simply to use the text as a source of problems and for back up reading, to use a fair amount of historical material and demonstrations in class, and to post my class notes on the web. Homework assignments include calculations based on historical experiments for example: Estimate the mechanical equivalent of heat using Rumford's cannon-boring data and Watt's estimate of one horsepower.
I strongly believe that it is not a waste of time to discuss some earlier theories that turned out to be wrong. In fact, these earlier theories are often close to the students' current thinking, so challenging them as to why those ideas were finally abandoned can stir the critical faculties and lead to better understanding.
A case in point is the caloric theory of heat. Of course, the students are vaguely aware that it's not right, but their intuitive ideas of heat, based on everyday experience, have probably led them to construct an operational model not too different from the caloric one, so we go ahead and discuss heat from this naive point of view, and mention the first recorded systematic experiments on heat and heat flow.
For example, Ben Franklin measured heat flow down rods of different materials by seeing how long it took to melt wax, and thereby compared the thermal conductivities of different materials, a matter of real practical importance in designing stoves, for example.
Franklin believed some weightless or almost weightless caloric fluid was flowing down those rods. Recall he'd thought the same thing about electricity—there was some electric fluid flowing when an object was being charged electrically—and there he was absolutely correct. Like the electric fluid, Franklin believed the caloric fluid would flow from one object to another, but overall there was always the same amount of fluid : it was conserved.
That is the basic Caloric Theory. We next discuss Joseph Black's ideas and careful experiments on heat, how it always flows from hot to cold things, and evens out in a room with no heat source after a time. I should mention that the evolution of thermometers up to Fahrenheit was covered immediately before this review of caloric theory. At this point, the quantitative concept of heat capacity is introduce deviating only slightly from historical correctness by using Celsius and grams from the start.
We perform one of Black's experiments in the lecture, using a calorimeter to find the specific heat of a piece of metal.
The students are asked to discuss and predict it first. Almost all of them expect the specific heat of copper to be greater than that for water, so the opposite result gets their attention. This naturally leads to a presentation of a wider range of results, and the mysterious finding of Dulong and Petit that the heat capacity per atom seems to be a constant, no matter what the weight of the atoms. Once we start thinking about atoms, it becomes clear that some kind of microscopic picture of the caloric fluid flow must be constructed.
OK, it wasn't clear to everyone at the time—even almost a century later, some eminent German scientists, such as Ostwald and Mach, were arguing against atomic models. They felt the business of science was the discovery of laws relating observable quantities, such as pressure, volume and temperature of a gas, and attempts to interpret these laws in terms of unobservable entities such as atoms were unverifiable fantasies.
Time has shown how wrong they were. Now only string theorists have to endure that kind of criticism! Anyway, back to the subject: our students certainly agree that some microscopic theory is needed, so how do we begin to construct one?
We know that heat expands a gas in class, we'd recently discussed Galileo's thermometer. How does the caloric theory explain that? Newton imagined atoms in a gas rather like soft oranges in a crate, taking up most of the room available, and coated with this caloric fluid, so that on pouring in more caloric the atoms swelled in size.
The atoms in a solid or liquid had a lot less caloric, that's why it took so much heat pumping in caloric to boil water. That sounds reasonable. But the caloric theory did much more: the whole theory of heat flow in solids, including important problems like the cooling of the earth over geological time, were analyzed quantitatively using sophisticated mathematical techniques developed in France by Fourier and others applied to the caloric theory, and these methods and results are all still good.
Furthermore, as we shall see shortly, Carnot developed a theory of the steam engine based on caloric theory, which was largely correct and shed new light on some of the most pressing technological problems of the era. But a caloric theory has to explain other things.
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