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Why is it that steel, when heated to redness and suddenly cooled, should assume such diamond-like hardness; that when similarly heated and slowly cooled it should become so soft; and that the hardened steel may so easily be tempered to any intermediate degree of hardness by simply raising it again to intermediate tem. peratures?
I endeavoured to reply to this question in a paper published in The Metallurgical Review (New York), of November 1877. My theory is based on some observations and experiments made some years previously in Sheffield.
I found that in certain samples of Spiegeleisen (composed of iron, manganese, and carbon) thin plates of well-formed crystals occurred here and there, forming a honeycombed structure by the crossing of the brilliant angular plates that stood out from the general mass. This general mass differed considerably in composition in different samples, while my analyses of the crystalline plates taken from various samples supplied at different times for the Bessemer works, showed that their composition was invariable as regards the proportion of the carbon to the iron, though the proportion of manganese was not so constant.
This fixed composition corresponded to the formula Fe, C (four equivalents of iron to one of carbon), indicating the existence of a definite chemical compound, not a mere indefinite variable mixture like that forming ordinary steel. The existence of such a compound is supported by the researches of many eminent metallurgists.
It is excessively hard, so brittle as to be useless for the purposes to which steel is applied, and it fuses at a much lower temperature than the fusing point of iron, or of any useful steel.
Iron, in its approximately pure state, is practically infusible in ordinary furnaces, but if pieces of such iron be thrown into a bath of melted steel, or melted pig-iron (which is rendered fusible by its impurities), the intractable wrought iron dissolves in the liquid like sugar in water, and is somehow diffused throughout it.
Steel is now made by thus melting wrought-iron scrap in fusible Spiegeleisen or ferro-manganese, or in selected pig-iron made from hæmatite. Steel generally contains from one-fourth to one-tenth of the amount of carbon contained in the Fe, C crystals.
My theory of the constitution of steel is that it is not a direct compound or mixture of iron and carbon, but an alloy of metallic iron with this metallic compound Fe, C; the mixture being capable of taking place in any proportions, as with other mixtures or alloys that are not true compounds.
When this mixture of materials of varying fusibility is heated, the more fusible assumes the semi-fluid or plastic condition, while the other remains solid. It has been proved that liquids expand and contract more than solids do when equally heated and cooled, and that this law applies to such compounds as the Fe,C.
What then must happen if such a mixture is suddenly cooled? Obviously a state of molecular tension due to unequal rates of contraction, an internal strain or pulling against each other of the iron and the carbon compound, the which tension constitutes hardness and brittleness. Slowly cooled they gradually yield and the molecular strain is thus diminished or prevented.
The fact that a given piece of steel when hardened is larger than when softened obviously supports this theory. In further support I cite the general fact that all alloys composed of metals of different fusibilities are harder than their constituents, or the mean of their constituents. Gun metal, bell metal, pewter, type metal, bronzes, the gold and silver alloy of our coins, are examples of this.
Some experiments have recently been made at Creusot by MM. Osmond and Werth which afford a remarkable confirmation of this theory; a direct physical demonstration, in fact.
They made thin sections of cast steel, attached them to glass by means of Canada balsam, treated them with cold dilute nitric acid, thereby dissolving the iron, and "leaving a residue of a nitro-derivative of a carbo-hydrate, and the skeleton thus obtained shows the distribution of the carbon in the original steel. It is found that fused steel (i.e. steel that has been fused) has a cellular structure, the nuclei consisting of pure iron and the envelopes of a carbide of iron. These simple cellules are grouped in compound cellules, the bounding surfaces of which are soft iron free from carbon.”
The above is quoted from the abstract of the paper in the May number of the “Journal of the Chemical Society;" the italics are my own. It further states that “when a bar of steel is dissolved, as in Weyl's method for the determination of carbon, the residue, which consists of a carbide of iron, retains the appearance and dimensions of the original bar, and it is seen that the small plates of the carbide form a network, within the meshes of which the pure iron was contained;" and also that “the compound cellules seem to be the result of independent dentritic aggregations, which have mutually limited each other and expelled from their lines of junction the still liquid carbide of iron."
The authors, while thus confirming my theory of the constitution of steel, do not seem to be acquainted with it, nor to perceive the
bearing of this structure on the much vexed question of the cause of the hardening and tempering of steel, concerning which some very queer theories have been propounded; such, for example, as affirming that the carbon is crystallized into diamonds, and these effect the hardening.
I hope my readers will understand that in using the term molecular strain or tension, I am not dreaming of ultimate molecules, but refer to physically demonstrable constituent particles. “Molecule” signifies a small mass.
THERE still remains among some good people the old idea that
T the so-called “instincts” of animals are divine inspirations, by means of which the animal performs its work with an excellence surpassing the possibilities of human attainment by human means of experience and teaching.
It is curious at this date to read the dialogues on instinct in Brougham's dissertations, and his mathematical demonstration of the absolute perfection of the structure of the cells of bees.
We now know that these miraculously perfect angles are the necessary results of the pressure of the wax upon itself.
Birds' nests are among the popular examples of this supposed infallibility. We are told in the old books that each species builds its nest of a fixed pattern, and does so without any instruction or copying.
So far from this being the case, it has been proved that birds hatched and reared in captivity are sad bunglers, as bad as amateur workmen of the human species, their nests being very clumsy structures, in some cases merely a heap of rubbish.
There is an interesting letter in Nature of April 9, by Mr. Charles Dixon, in which he states that chaffinches taken to New Zealand and there set at liberty have evidently fallen into a state of mental confusion by imperfect remembrance of the architecture of their old homes, and mixing these reminiscences with the impressions produced by contemplating those of their new neighbours. The result is a confused imitation of both the New Zealand “lang nests” and those of the British chaffinch; and this, according to Mr. Dixon's description, must be almost as barbarous as some of the suburban architectural excrescences in which recently migrated citizens attempt to combine in a villa residence the features of a London street house with those of an antique rural cottage or a parish church.
Mr. Dixon has a photograph of one of these “Queen Anne" chaffinch nests. It should be carefully preserved and others taken, to supply a record of the progress of these emigranis, in order that we may learn whether they will gradually revert towards the original type of their parents, or move in the direction of more closely and skilfully copying the domestic architecture of their new neighbours. Such a record will assist in the solution of some of the much debated instinct problems.
INCUBATION AND MAGNETISM.
A N old writer described prejudice as “the spider of the mind," A seeing its resemblance to the spider which hangs its web in all places ; in the humblest cottage and the noblest mansion alike; therefore, says this good monitor, beware to sweep from the dwelling of your mind the cobwebs thus ubiquitously woven.
I am reminded of this sage advice whenever I come upon any hypothesis which invokes electricity or magnetism to the explanation of obscure phenomena.
This is now the case in reading an account of the experiments of some of the modern Lincei (see their Rendiconti of December 14. 1884). Professor Maggiorani and Dr. Magini have been magnetising eggs in an incubator, and find that the action of the magnets is retarding, that none of the eggs escape this retarding action, and that it is proportional to the power of the magnets.
When further I learn that Professor Maggiorani concludes his paper by suggesting that the magnetism interferes by virtue of its analogy to vital force, my cobwebs become very thick, in spite of my veneration of the ancient fraternity of the lynx-eyed. This habit of explaining everything which is not understood by the mysterious agency of these forces is becoming something like a superstition.
W. MATTIEU WILLIAMS.
PROPOSED RESTORATION OF THE CHURCH OF ST. BARTHOLOMEW
I T is to be trusted that no lack of funds or other cause will inter1 fere with the proposed task of restoring the church of St. Bartholomew the Great, Smithfield. One of the earliest churches of the Austin Canons in England, a generation later in date than the chapel in the White Tower, it affords an admirable illustration of the state of architecture in England in the days of Henry I., and is a priceless ecclesiastical monument. Its present state is a disgrace to London. The apse is occupied as a fringe manufactory, which projects over the east end of the church and overhangs the altar, being supported by iron columns within the altar rails; the site of the north transept is taken up by a blacksmith's forge and a dwellinghouse; the north triforium holds the parochial boys' school, and the chapter house the girls' and infants' schools. That the inclusion within the building of these establishments interferes with the conduct of service, and is in every sense an indecency, will be granted. It is, however, with the antiquarian loss such a state of affairs involves, rather than with the desecration of a building intended for worship, I am concerned. Those who know the value, historical and architectural, of such early specimens of Norman workmanship, can scarcely be deaf to the appeal now made for funds to clear from encumbrance and restore to ecclesiastical uses what remains of the edifice. At the present moment exceptional facilities for the acquisition of the portion of the building now misapplied are furnished. The sum required seems large, but is nothing when the importance and value of the restoration are taken into account. All necessity to dwell upon the features of the church is fortunately spared. In the Gentleman's Magazine for October, 1863, appears the substance of a lecture by Mr. J. H. Parker, F.S A., delivered on the church, and subsequently reprinted as a pamphlet. From this a full account can be obtained of the edifice, and in it will be found the most eloquent and convincing appeal in favour of the proposed restoration. VOL, CCLVIIĮ. NO. 1854.