2020 RETA Breeze Jan-Feb

Per the paper Benjamin Thompson

As most stories begin, while hard at work one day. Benjamin asked himself “Whence comes the heat produced in the mechanical operations of boring cannon? Is it furnished by the metallic chips which are separated from the metal?” This began, the quest for the answer. Traditional thought being that the boring process was releasing latent heat in the brass. Experiments proved this to be false as the amount of latent heat which could be absorbed by a pound of brass was the same whether previously bored or not. In his next experiment Benjamin, horizontally mounted a cylinder. He then bored a 1.75” radius hole in the end. He inserted a flat piece of hardened steel 4” inches long, .63” thick, and nearly 3”wide. This provided a 2.5” area of contact. A small hole was then cut in which he inserted a mercury thermometer. This allowed Benjamin a means by which the heat could be measured. Using a weight to create pressure and thus assure friction, he spun the cylinder at 32 Revolutions per minute. The temperature made prior to the rotation was 60 degrees. After 30 minutes and approximately 960 rotations, the temperature of the cylinder was 130 degrees. The experiment was a success. He would perform further experiments to determine the mechanical equivalency of heat As a point of reference, it should be noted that at the time of the American Revolution, the Royal Society of England was one of the most prestigious Science organizations in the world. For one’s work to obtain legitimacy, it must be submitted and subjected

“A quadrangular oblong deal box (Fig. 1) watertight, 11.5 English inches long, 9.4 inches wide, and 9.6 inches deep (measured in the clear), being provided with holes, or slits, in the middle of each of its ends, just large enough to receive, the one, a square iron rod, to the end of which the blunt steel borer was fastened; the other, a small cylindrical neck,

presented to the Society:

which joined the hollow cylinder to the cannon, when this door (which was occasionally closed above by a wooden cover, or lid. moving on hinges) was put into its place; that is to say, when by means of the two vertical openings, or slits, in its two ends (the upper parts of which openings were occasionally closed by means of narrow pieces of wood sliding in vertical grooves), the box (g, h, I, k, Fig.2) was fixed to the machinery in such a manner that its bottom (I, k) being in the plane of the horizon, its axis coincided with the axis of the hollow metallic cylinder, it is evident from the description that the hollow metallic cylinder would occupy the middle of the box without touching it on either side, and that, on pouring water into the box, and filling it to the brim, the cylinder would be completely covered, and surrounded on every side, by that fluid. And, farther, as the box was held fast by the strong square iron rod in which passed in a square hole in the center of one of its ends (a, fig. 1) while the round or cylindrical neck, which joined the hollow cylinder to the end of the cannon, could turn round freely on its axis in the round hole in the center of the other end of it, it is evident that the machinery could be put in motion without the least danger of forcing the box out of its place, throwing the water out of it, or rearranging any part of the apparatus.”

“Everything being ready, I proceeded to make the experiment I had projected, in the

following manner:”

“The hollow cylinder having been previously cleaned out and the inside of its bore wiped with a clean towel till it was quite dry, the square iron bar, with the blunt steel borer fixed to the end of it, was put into its place,

14 RETA.com / The Refrigeration Historian