Heat is a Form of Motion: An Experiment in Boring Cannon

Benjamin Thompson (Count Rumford)
Philosophical Transactions (vol. 88), 1798

It frequently happens that in the ordinary affairs and occupations of life opportunities present themselves of contemplation some of the most curious operations of nature; and very interesting philosophical experiments might often be made, almost without trouble or expense, by means of machinery contrived for the mere mechanical purposes of the arts and manufactures.

I have frequently had occasion to make this observation, and am persuaded that a habit of keeping the eyes open to everything that is going on in the ordinary course of the business of life has oftener led, as it were by accident, or in the playful excursions of the imagination, put into action by contemplating the most common appearance, than all the more intense meditation of philosophers, in the hours expressly set apart for study.

It was by accident that I was led to make the experiments of which I am to give an account; and, though they are not perhaps of sufficient importance to merit so formal an introduction, I cannot help flattering myself that they will be thought curious in several respects, and worthy of the honor of being made known to the Royal Society.

Being engaged, lately, in superintending the boring of cannon, in the workshops of the military arsenal at Munich, I was struck with the very considerable degree of heat which a brass gun acquires, in a short time, in being bored; and with the still more intense heat ( much greater than that of boiling water, as I found by experiment) of the metallic chips separated from it by the borer.

The more I meditated on these phenomena the more they appeared to me to be curious and interesting. a thorough investigating of them seemed even to bid fair to give a farther insight into the hidden nature of heat; and to enable us to form some reasonable conjectures respecting the existence, or non- existence, of an igneous fluid: a subject on which the opinions of philosophers have, in all ages, been much divided.

In order that the society may have clear and distinct ideas of the speculations and also of the specific objects of philosophical investigation they suggested to me, I must beg leave to state them at some length and in such manner as I shall think best to answer this purpose.

From whence comes the heat actually produced in the mechanical operation above mentioned?

Is it furnished by the metallic chips which are separated by the borer from the solid mass of metal?

If this were the case, then, according to the modern doctrines of latent heat, and of caloric, the capacity for the heat of the parts of the metal, so reduced to chips, ought not only to be changed, but the change undergone by them should be sufficiently great to account for all the heat produced.

But no such change had taken place; for I found, upon taking equal quantities, by weight, of these chips, and of thin slips of the same block of metal separated by means of a fine saw, and putting them at the same temperature (that of boiling water) into equal quantities of cold water (that is to say, at the temperature of 59 1/2 °F), the portion of the water into which the chips were put was not, to all appearance, heated either less or more than the other portion, in which the slips of metal were to put.

This experiment being repeated several times, the results were always so nearly the same that I could not determine whether any, or what change, had been produced in the metal, in regard to its capacity for heat, by being reduces to chips by the borer.

From hence it is evident that the heat produces could not possibly have been furnished at the expense of the latent heat of the metallic chips. but, not being willing to rest satisfied with these trails, however conclusive they appeared to me to be, I had resource to the following still more decisive experiment:

Taking a cannon (a brass six-pounder) cast solid, and rough as it came from the foundry, and fixing it (horizontally) in the machine used for boring, and at the same time finishing the outside of the cannon by turning, I caused its extremity to be cut off; and, by turning down the metal in that part, a solid cylinder was formed, 7 3/4 inches in diameter, and 9 8/10 inches long

This short cylinder, which was supported in its horizontal position, and turned round its axis, by means of the neck by which it remained united to the cannon, was now bored with the horizontal borer used in boring cannon .

This cylinder being designed for the express purpose of generating heat by friction, by having a blunt borer forced against its solid bottom at the same time that it should be turned round its axis by the force of horses, in order that the heat accumulated in the cylinder might from time to time be measured, a small round hole, 0.37 of an inch only in diameter, and 4.2 inches in depth, for the purpose of introduction a small cylindrical mercurial thermometer, was made in it. .

This experiment was made in order to ascertain how much heat was actually generated by friction, when a blunt steel borer being so forcibly shoved (by means of a strong screw) against the bottom of the bore of the cylinder that the pressure against it was equal to the weight of about 10,000 pounds avoirdupois, the cylinder was turned round on its axis (by the force of horses) at the rate of about thirty-two times in a minute . . . .

To prevent, as far as possible, the loss of any part the heat that was generated in the experiment, the cylinder was well covered up with a fit coating of thick and warm flannel, the cylinder was carefully wrapped round it, and defended it on every side from the cold air of the atmosphere.

At the beginning of the experiment the temperature of the air in the shade, as also that of the cylinder, was just 60 °F.

At the end of thirty minutes, when the cylinder had made 960 revolutions about its axis, the horses being stopped, a cylindrical mercurial thermometer, whose bulb was 32/100 of an inch in diameter, and 3 1/4 inches in length, was introduced into the hole made to receive it, in the side of the cylinder, when the mercury rose almost instantly to 130 °F . . . .

Finding so much reason to conclude that the heat generated in these experiments, or excited, as I would rather choose to express it, was not furnished at the expense of the latent heat or combined caloric of the metal, I pushed my inquiries a step farther and endeavored to find out whether the air did, or did not, contribute anything in the generation of it . . . .

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, it was put into its place; the mouth of the bore of the cylinder being closed at the same time, by means of the circular piston, through the center of which the iron bar passed.

This being done, the box was put in its place, and the joining of the iron rod, and of the neck of the cylinder, with the two ends of the box, having been with cold water (viz., at the temperature of 60 °F) and the machine was put in motion.

The result of this beautiful experiment was very striking, and the pleasure it afforded me amply repaid me for all the trouble I had had in contriving and arranging the complicated machinery used in making it.

The cylinder, revolving at the rate of about thirty-two times in a minute, had been in motion but a short time when I perceived, by putting my hand into the water and touching the outside of the cylinder, that heat was generated; and it was not long before the water which surrounded the cylinder began to be sensibly warm.

At the end of one hour I found, by plunging a thermometer into the water in the box ( the quantity of which fluid amounted to 18.77 pounds avoirdupois, or 2 1/4 wine gallons) that its temperature had been raised no less than 47 degrees; being now 107° of Fahrenheit's scale.

When thirty minutes more had elapsed, or one hour and thirty minutes after the machinery had been put in motion, the heat of the water in the box was 142 °F.

At the end of two hours, reckoning from the beginning of the experiment, the temperature of the water was found to be raised to 178 °F.

At two hours twenty minutes it was 200 °F; and at two hours thirty minutes it actually boiled!

It would be difficult to describe the surprise and astonishment expressed in the countenances of the bystanders, on seeing so large a quantity of cold water heated and actually made to boil without any fire.

Though there was, in fact, nothing that could justly be considered as surprising in this event, yet I acknowledge fairly that it afforded me a degree of childish pleasure, which, were I ambitious of the reputation of a grave philosopher, I ought most certainly rather to hide to than to discover.

The quantity of heat excited and accumulated in this experiment was very considerable; for not only the water in the box, but also the box itself (which weighted 15 1/4 pounds) and the hollow metallic cylinder, and that apart of the iron bar which, being situated within the cavity of the box, was immersed in the water, were heated 150 degrees of Fahrenheit's scale; viz. , from 60 °F (which was the temperature of the water, and of the machinery, at the beginning of the experiment) to 210 °F, the heat of boiling water at Munich.

The total quantity of the heat generated may be estimated with some considerable degree of precision . . . .

From the result of these computation it appears that the quantity of heat produced equably, or in a continual stream (if I may use that expression), by the friction of the blunt steel borer against the bottom of the hollow metallic cylinder, in the experiment under consideration, was greater than that produced equably in the combustion of nine wax candles, each three quarters of an inch in diameter, all burning together, or at the same time, with clear bright flames.

As the machinery used in this experiment could easily be carried round by the force of one horse (though, to render the work lighter, two horses were actually employed in doing it), these computations show further how large a quantity of heat might be produced by proper mechanical contrivance, merely by the strength of a horse, without either fire, light, combustion, or chemical decomposition; and, in a case of necessity, the heat thus produces might be used in cooking victuals.

But no circumstances can be imagined in which this method of procuring heat would not be disadvantageous; for more heat might be obtained by using the fodder necessary for the support of a horse, as fuel.

By meditating on the results of all these experiments we are naturally brought to that great question which has so often been the subject of speculation among philosophers; namely:

What is heat? Is there any such thing as an igneous fluid? Is there anything that can with propriety be called caloric?

We have seen that a very considerable quantity of heat may be excited in the friction of two metallic surfaces and given off in a constant stream or flux, in all directions, without iteration or intermission, and without any signs of diminution or exhaustion.

From whence came the heat which was continually given off in this manner, in the foregoing experiments? Was it furnished by the small particles of metal, detached from the larger solid masses, on their being rubbed together? This, as we have already seen, could not possibly have been the case.

Was it furnished by the air? This could not have been the case; for in there of the experiments, the machinery being kept immersed in water, the access of the air of the atmosphere was completely prevented.

Was it furnished by the water which surrounded the machinery? That this could not have been the case is evident: first, because this water was continually receiving heat from the machinery and could not, at the same time, be giving to, and receiving heat from, the same body; and secondly, because there was no chemical decomposition of any part of this water. had any such decomposition taken place (which indeed could not reasonably have been expected), one of its component elastic fluids (most probably inflammable air) must, at the same time, have been set at liberty, and in making its escape into the atmosphere would have been detected; but though I frequently examined the water to see if any air bubbles rose up through it, and had even made preparations for catching them, in order to examine them, if any should appear, I could perceive none; nor was there any sign of decomposition of any kind whatever, or other chemical process, going on in the water.

Is it possible that the heat could have been supplied by means of the iron bar to the end of which the blunt steel borer was fixed? Or by the small neck of gun metal by which the hollow cylinder was united to the cannon? These suppositions appear more improbable even than either of these before mentioned; for heat was continually going off, or out of the machinery, by both these passages, during the whole time the experiment lasted.

And, in reasoning on this subject, we must not forget to consider that most remarkable circumstance, that the source of the heat generated by friction, in these experiments, appeared evidently to be inexhaustible.

It is in hardly necessary to add that anything which any insulated body, or system of bodies, can continue to furnish without limitation cannot possibly be a material substance: and it appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of anything, capable of being excited and communicated, in the manner the heat was excited and communication in these, except it be MOTION.