Properties of Steel-Hard caft Iron.

105

We have remarked that cast iron, fufficiently abounding with charcoal, affumes the appearance of the white crude iron when it is cast in plates or too fuddenly cooled. To afcertain its nature, nothing more is neceffary than to clean its surface; and by the more or lefs grey or dark colour of the spot produced by nitrous acid, a judgment may be formed of its quality.

VANDERMONDE, MONGE, BERTHOLLET.

Annotations upon the Report concerning Steel.

1. NOTWITHSTANDING the great light which has been afforded by the labours of Rinman, Bergman, Vauquelin, and other chemifts, together with the learned authors of the foregoing paper, we have still much to learn refpecting the caufes of the feveral qualities of fteel to be found in the market. Much of this information might probably be obtained by diligent enquiry, and the ufual methods of examination. It is yet to be fhewn by experiment, whether pure iron united with carbon conftitutes the beft fteel; or whether any additional ingredient, such as phosphorus, manganese, or other metallic matter, may not be of advantage. If the former pofition be true, the beft fteel-iron will be that which is the pureft; and the best cement will be the fimpleft coaly matter. On the contrary, if the latter suppositions should be well founded, the goodness of our steel will depend, not only upon the component parts of the bar iron, but likewife on the adaptation of the cement proper for its converfion. Mr. Duhamel, in the Encyclopédie, article Acier, p. 462, found that the charcoal which had been used in making steel was not fit to be used again, by reason of the flowness of its operation. In this cafe it feems probable that, though enough of carbone remained, yet fome more volatile ingredient had been expended in the first procefs. Our authors have well explained the advantage of the iron being well forged and found throughout, previous to its expofure to the cementing process.

2. The grey crude iron may be confidered as iron faturated with as much plumbago or carburet as it can hold in folution at a very elevated temperature. When it is fuffered to cool flowly, as in foft cafting, the plumbago appears to separate by hafty crystallization through the whole mafs, as may frequently be observed in its fracture, and as has been shewn by plunging a cold bar of iron into the fused metal, and withdrawing it covered with the carburet which precipitates upon it. When this iron is poured into a cold mould of metal, or suffered to run to a great distance from the aperture of reception, in sand, or otherwife if a bar of this metal be heated to whitenefs, and plunged in water, it becomes very hard; more fo than steel tools of any defcription are usually made, and is very white, and clofer grained in its fracture. The hardness must depend upon circumstances in its aggregation, to explain which we poflefs no data; but I apprehend the whitenefs to be an evident confequence of the union between the iron and the plumbago continuing to be nearly as intimate as it was at the white heat. It is very probable that, in all cafes of the hardening of other feels containing lefs carbone, a fimilar effect may take place.

3. The laminating rollers, concerning which our authors offer nothing but conjecture, are made of this iron caft in fand, or metallic moulds of confiderable thickness. I am informed by founders who make them, that the external hard part does not penetrate to a greater depth than about three quarters of an inch; and that the hardness is not greater than that of a good graver. The procefs of turning them in the lathe, in fact, fhews this. VOL. II.-JUNE 1798. P

For

106

Properties of Steel-Heat excited by Friction.

For they are turned by an extremely flow motion, with a tool selected from the general stock in the work-fhop, because the greater number even of good gravers will not cut it.

4. Thofe who forge fteel know that it is very eafily degraded in the fire. If a fmallpiece, for example, half a cubic inch, of grey crude iron be put into a common fire, and kept red-hot for about half an hour, and at the expiration of that time the heat be fuddenly raised to whitenefs by the bellows; the internal or fteely part will break its way through the external cruft, which is converted into common iron, and rendered much less fufible. This cruft, or hollow fhell, may then be taken out of the fire. All fteel becomes degraded in the fame manner, even by very careful heating. Caft-fteel, drawn into fmall bars, exhibits cloudy lines and veins on its furface when tried by an acid, which no doubt have been produced during the heating and forging.

5. Caft-fteel being made out of broken tools of every kind, cannot of itself poffefs a larger dofe of plumbago than the average quantity contained in thofe fteels. But the English caftfteel is more fufible and more tender under the hammer than German fteel, or the steel of cementation; which circumstances appear to indicate that it contains more plumbago: and the truth of this induction is confirmed by its exhibiting a much darker fpot than other fteels, when tried by an acid. Chalut did not therefore make this kind of fteel when he ufed glafs only for his flux. It cannot be doubted but that the flux of our manufacturers. must contain charcoal, at leaft. If it be animal coal, which is most probable, it will also contain phosphorus; an ingredient to which the fuperiority of this coal, in cafe-hardening, is probably owing.

6. Tenacity and hardness are very frequently confidered as if they were one and the fame quality with regard to implements and tools, though they are certainly very distinct properties. Tenacity is the oppofite to friability or brittleness; hardness is the opposite to foftness. It is probable that iron is more tenacious than steel, and it is certain that soft fteel is more tenacious than hard. Where tenacity and no confiderable degree of hardness are wanting, as in springs, the inferior steels, or the compounds of steel and iron, will afford a more fafe, and confequently in many inftances more ufeful article; but where hardness and tenacity are both required, the leading quality of the steel must be its uniformity: Cast. fteel is preferred in England to every other kind, not only for polished steel-work and the best cutting tools, but likewise for cold chisels, and the hard gravers for turners in metal; in both which laft I have obferved, by confiderable experience, that the common opinion is well founded.

III.

An Enquiry concerning the Source of the Heat which is excited by Friction*. By BENJAMIN, COUNT of RUMFORD, F.R.S. M.R.I.A.

IT frequently happens that, in the ordinary affairs and occupations of life, opportunities

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present themselves of contemplating fome of the most curious operations of nature; and

From the Philofophical Tranfactions, 1798.-Read January 25, 1798.

Heat excited in boring Cannon.

107 very interesting philofophical experiments might often be made, almost without trouble or expence, by means of machinery contrived for the mere mechanical purposes of the arts and manufactures.

I have frequently had occafion to make this obfervation; and am perfuaded, that a habit of keeping the eyes open to every thing that is going on in the ordinary courfe of the bufinefs of life, has oftener led, as it were by accident, or, in the playful excurfions of the imagination put into action by contemplating the most common appearances, to useful doubts and ferviceable schemes for investigation and improvement, than all the more intenfe meditations of philofophers in the hours exprefsly fet apart for study.

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

Being engaged, lately, in fuperintending the boring of cannon in the workshops of the military arsenal at Munich, I was struck with the very confiderable degree of heat which a brafs gun acquires in a short time in being bored, and with the 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 interefting. A thorough inveftigation of them feemed even to bid fair to give a farther infight 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 philofophers have in all ages been much divided.

In order that the Society may have clear and diftinct ideas of the fpeculations and reafonings to which thefe appearances gave rife in my mind, and alfo of the fpecific objects of philofophical invefligation they fuggefted to me, I must beg leave to ftate them at fome length, and in fuch manner as I fhall think beft fuited 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 feparated by the borer from the folid mafs of metal?

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

But no fuch change had taken place; for I found, upon taking equal quantities by weight of thefe chips, and of thin flips of the fame block of metal, feparated by means of a fine faw, and putting them at the fame temperature (that of boiling water) into equal quantities of cold water (that is to fay, at the temperature of 591° F.), the portion of water into which the chips were put was not, to all appearance, heated either lefs or more than the other portion into which the flips of metal were put.

This experiment being repeated feveral times, the refults were always fo nearly the fame,

108

Experiments to fhew that Heat excited by Friction

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 reduced to chips by the borer*.

From hence it is evident, that the heat produced could not poffibly have been furnished at the expence of the latent heat of the metallic chips. But, not being willing to reft fatiffied with thefe trials, however conclufive they appeared to me to be, I had recourfe to the following ftill more decifive experiment.

Taking a cannon (a brafs fix pounder) caft folid, and rough as it came from the foundry, (fee fig. 1, plate V) and fixing it (horizontally) in the machine used for boring, and at the fame time finishing the outside of the cannon by turning, (fee fig. 2.) I caused its ex-tremity to be cut off, and, by turning down the metal in that part, a folid cylinder was formed, 7 inches in diameter, and 9 inches long; which, when finifhed, remained joined to the rest of the metal (that which, properly speaking, conftituted the cannon,) by a small cylindrical neck, only 2 inches in diameter, and 3 inches long.

8 TO

This fhort cylinder, which was fupported in its horizontal pofition, 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; but its bore, which was 3.7 inches in diameter, instead of being continued through its whole length, (9.8 inches) was only 7.2 inches in length; fo that a folid bottom was left to this hollow cylinder, which bottom was 2.6 inches in thickness.

This cavity is represented by dotted lines in fig. 2; as also in fig. 3, where the cylinder is reprefented on an enlarged fcale.

This cylinder being defigned for the express purpose of generating heat by friction, by having a blunt borer forced against its folid bottom at the fame 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, (see d, e, fig. 3.) 0.37 of an inch only in diameter, and 4.2 inches in depth, for the purpose of introducing a small cylindrical mercurial thermometer, was made in it, on one fide, in a direction perpendicular to the axis. of the cylinder, and ending in the middle of the solid part of the metal which formed the bottom of its bore.

As these experiments are important, it may, perhaps, be agreeable to the Society to be made acquainted with them in their details. One of them was as follows:

To 4590 grains of water, at the temperature of 591° F. (an allowance or compenfation, reckoned in water, for the capacity for heat of the containing cylindrical tin veffel, being included) were added 10164 grains of gun-metal in thin flips, feparated from the gun by means of a fine faw, being at the temperature of 210° F. When they had remained together 1 minute, and had been well stirred about by means of a small rod of light wood, the heat of the mixture was found to be = 63°.

From this experiment, the specific heat of the metal, calculated according to the rule given by Dr. Crawford, turns out to be = 0.1100, that of water being = 1.000.

An experiment was afterwards made with the metallic chips, as follows:

To the fame quantity of water as was used in the experiment above mentioned, at the fame temperature, (viz. 5940,) and in the fame cylindrical tin veffel, were now put 1016 grains of metallic chips of gun-metal, bored out of the fame gun from which the flips used in the foregoing experiment were taken, and at the fame temperature (210°.) The heat of the mixture, at the end of 1 minute, was just 630, as before; confequently the specific heat of thefe metallic chips was 0.1100. Each of the above experiments was repeated three times, and always with nearly the fame results.

The

The folid contents of this hollow cylinder, exclufive of the cylindrical neck by which it remained united to the cannon, were 385 cubic inches, English meafure, and it weighed 113.13 lb. avoirdupois, as I found on weighing it at the end of the courfe of experiments. made with it, and after it had been feparated from the cannon with which, during the experiments, it remained connected *.

Experiment No. 1.

THIS experiment was made in order to afcertain how much heat was actually generated by friction, when a blunt fteel borer being fo forcibly fhoved (by means of a strong screw) against the bottom of the bore of the cylinder, that the preffure against it was equal to the weight of about 10,000 lb. avoirdupois, the cylinder was turned round on its axis. (by the force of horses) at the rate of about 32 times in a minute.

This machinery, as it was put together for the experiment, is represented by fig. 2. W is a strong horizontal iron bar connected with proper machinery carried round by horfes, by means of which the cannon was made to turn round its axis.

To prevent, as far as poffible, the loss of any part of the heat that was generated in the experiment, the cylinder was well covered up with a fit coating of thick and warm flannel, which was carefully wrapped round it, and defended it on every fide from the cold air of the atmosphere. This covering is not reprefented in the drawing of the apparatus, fig. 2.

I ought to mention, that the borer was a flat piece of hardened fteel, 0.63 of an inch. thick, 4 inches long, and nearly as wide as the cavity of the bore of the cylinder, namely, 3 inches. Its corners were rounded off at its end, so as to make it fit the hollow bottom of the bore; and it was firmly fastened to the iron bar (m), which kept it in its place. The area of the furface, by which its end was in contact with the bottom of the bore of the cylinder, was nearly 2 inches. This borer, which is distinguished by the letter n, is represented in most of the figures.

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

32

At the end of 30 minutes, when the cylinder had made 960 revolutions about its axis, the horses being stopped, a cylindrical mercurial thermometer, whofe bulb was of an inch in diameter, and 34 inches in length, was introduced into the hole made to receive it, in the fide of the cylinder; when the mercury rofe inftantly to 130.

Though the heat could not be supposed to be quite equally diftributed in every part of the cylinder, yet, as the length of the bulb of the thermometer was fuch that it extended

* For fear I should be fufpected of prodigality in the profecution of my philofophical researches, I think it neceffary to inform the Society, that the cannon I made ufe of in this experiment was not facrificed to it. The short hollow cylinder which was formed at the end of it, was turned out of a cylindrical mass of metal about two feet in length, projecting beyond the muzzle of the gun, called in the German language the verlorner kopf, (the head of the cannon to be thrown away,) and which is reprefented in fig. 1.

This additional projection, which is cut off before the gun is bored, is always caft with it, in order that, by means of the preffure of its weight on the metal in the lower part of the mould, during the time it is cooling, the gun may be the more compact in the neighbourhood of the muzzle, where, without this precaution, the metal would be apt to be porous or full of honeycombs.

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