quently no separation of distinct compounds can take place on cooling. "But if the carbon be in slight excess, the whole of the iron will first be converted into steel; then the free carbon which remains in the crucible will combine in a new proportion with a part of the fused steel already formed, and there will thus be two distinct compounds, pure steel, and carburetted or cast steel. These two compounds, at first indiscriminately mingled together, will tend to separate as soon as the liquid matter is at rest, and crystallization will ensue, during which the molecules of the two compounds will arrange themselves according to their respective affinities and weights.

"If we dip a blade made of steel thus prepared in acidulated water, a very evident damask will be developed, in which the portions of pure steel will be black, and those of the carburetted will remain white, because the acidulated water does not so readily lay bare the carbon of the carburetted steel as of the pure.

"It is, therefore, to the irregular division of the carbon by the metal, and the formation of two distinct compounds, that the production of the damasked surface is to be attributed, and it is obvious that the more gradually the mass is cooled, the larger will be the veins of the damask. It is, perhaps, for this reason, that we should avoid fusing the substance in too great a mass, or at least that some limit should be observed in the process; in support of which opinion 1 may quote Tavernier, who has given in his "Voyage en Perse some information as to the size of the balls of steel, which, in his day, were used in making the damasked blades.

"The steel capable of being damasked comes, says he, from the kingdom of Golconda; it occurs in commerce in masses of the size of a halfpenny loaf; they are cut in two to see if they be of good quality, and each half makes one sword blade.

"From this account it is evident, that this Golconda steel was in buttons like wootz, and that each button could not have weighed more than five or six pounds.

"Tavernier adds, that if this steel were tempered by the European processes, it would be as brittle as glass. Hence, as Reaumur observed, it must be very difficult to forge.

"That philosopher having received some specimens of Indian steel from Cairo found no one in Paris who could forge it; whereupon he laid the blame on our workmen; since the inhabitants of the east know how to work that kind of steel. explain presently the proper method of proceeding to ensure

success.

I will

"As carbon has the chief influence not only in producing the damask on steel, but also on its intrinsic qualities, I fear that Messrs. Stodart and Faraday were led into error in their experiments (as I, for a long time, was myself), and attributed effects

to metallic alloys which were owing more particularly to an increased proportion of carbon.

"I am very far from disputing the existence of metallic alloys in the oriental sabres, although, in the few fragments which I have had an opportunity of examining, I have not found either silver, gold, palladium, or rhodium; I think it very probable, however, that different combinations may have been attempted. A people who knew how to harden copper by alloying it with other metals, are very likely, from analogy, to have tried the same process with iron.

"This view of the subject led me to form various metallic alloys, some of which gave satisfactory results. One of the sword blades which I presented to the Exhibition contains onehalf per cent. of platina, and a larger proportion of carbon than common steel; its damask is owing particularly to the latter. Excellent razors have been made with this alloy.

"At all events these alloys should not be tried till we have fully ascertained the effects of pure carbon, and we ought to begin by combinations in very small proportions. The addition of a metal makes the steel more brittle; however, I have obtained ductile alloys, in raising the quantity of gold and platina, as high as 4 per cent. and that of copper and zinc to 2.

"As to zinc, certain precautions are necessary in forming alloys with that metal; it occasions violent detonations, wherefore it must be added to the fused metals in very small portions at a time. In forging steel alloyed with zinc, part of the metal is volatilized and dissipated.

"Manganese unites readily with steel, and the alloy forges easily; but it is very brittle when cold: I have made gravers with this alloy which cut iron without having been tempered: the damask of this mixture is very black and well defined.

66

Plumbago appeared in some instances to soften steel which had been rendered too brittle by an excess of carbon; at least I have obtained excellent results with 100 parts of steel, 1 of lamp-black, and 1 of plumbago.

"But a very remarkable experiment, from the advantage that may result from it in working on a large scale, is one which showed that 100 parts of soft iron and 2 of lamp-black fuse as readily as common steel. Probably the whole of the carbon does not combine. Some of our best blades are produced from this combination. It has the disadvantage of contracting very much on cooling, and the buttons generally have cavities which make them very difficult to forge; but if, instead of damasked, we only want to make common steel, the contraction on cooling may be prevented by casting this compound in an ingot mould. "This experiment teaches us that the previous cementation of the iron is not necessary in order to obtain very good steel.

It may be treated at once with lamp-black, which will very much lessen the expense of the manufacture.

"One hundred parts of very grey cast iron filings, and 100 parts of the same filings previously oxidated, gave a steel of a fine damask, and calculated for sword blades, &c. It is remarkable for its elasticity, an important quality in which the Indian steel is deficient. I have always operated on three or four pounds at a time. The larger the proportion of the oxidated ingredient, the tougher (nerveux) is the steel. The oxygen combining with the metals of the earths, and part of the carbon, it is obvious that the more oxide there is, the more ductile will be the result; but it will also be softer. The blackest cast iron answers best. I am convinced that with that substance we may make cast steel in reverberatory furnaces on a very large scale, by adopting a process analogous to that used in refining bell metal, namely, by adding to the fused metal a portion of the same metal oxidated; or, still better, native oxide of iron.

"It seems to me to be equally practicable to convert the whole of the product of the Catalonian forges (forges à la Catalane) into cast stecl, by altering the construction of the furnaces so as completely to fuse the metal. I think if I had the direction of one of those forges, I could find means to manufacture steel of the most desirable quality with great saving of expense.

“I have always been careful to stir the fused metal thoroughly before I suffered it to cool; this is indispensable in making metallic alloys, for without it the damask is not homogeneous.

"It was after I had attempted to combine steel with aluminum and silicium, that I observed the influence of carbon in producing the damask: from that time I always used the carbon of lamp-black.

"If some earths be found on analyzing my cast steel, they must probably be attributed to the cast iron employed, or to the iron, the plumbago, or the crucibles.

"The more carbon a steel contains, the more difficult it is to forge. The greater number of those that I have prepared can be tilted at only very limited temperatures. At a white heat they crumble under the hammer; at a cherry-red they become hard and brittle, and this quality increases in proportion as the temperature diminishes; so that when once it has fallen below cherry-red, if we endeavour to cut it with the graver, or the file, we find it much harder and more brittle than after it is completely cold.

"It is evident that the Indian steel, which most of our workmen are unable to forge, is similarly circumstanced; and if the Indians work it without difficulty, it is because they know the limits of temperature within which it is manageable.

"I am convinced from experience that the orbicular veins,

which the workmen call brambles (ronce), and which are seen on the beautiful Indian blades, are the consequence of the way in which they are forged. If steel be drawn out lengthwise, the veins will be longitudinal; if it be equally extended in all directions, the damask will have a crystalline appearance; if it be rendered wavy in both directions, it will be shaded like the eastern damask. But few trials are necessary to produce any sort of watering that may be desired.

"The best process for developing the damask, so that the steel may become black or bluish without losing its polish, is, in my opinion, that which is employed in the East. It is described, by M. le Vicompte Héricart de Thury, in a report inserted in the Bulletin de la Société d'Encouragement,' No. 220, for December, 1821, twentieth year, p. 361.”

ARTICLE XI.

The Bakerian Lecture.-On certain Motions produced in Fluid
Conductors when transmitting the Electric Current.
J. F. W. Herschel, Esq. FRS.

(Concluded from p. 176.)

By

17. In many liquids, and especially in solutions of the nitrates, there is formed not only a current radiating from the negative pole, but also one from the positive, which even has in some cases a preponderance over the other. These co-exist in the mercury; and, in consequence of their action, a zone of equilibrium is formed in the globule, nearer to one or the other pole, as the antagonist current is more or less violent. The best way to render the influence of this counter-current sensible is to operate on a large quantity of mercury, under dilute solutions, keeping the negative pole at a distance, and the positive very near. In this way there are few liquids which, when the pile is in good action, do not show some signs of a counter-current from the positive pole. The cause of this will be evident, when we come to speak of the action of metallic alloys.

18. If either pole be brought in contact with the mercury, no currents are observed from the point of contact (at least when the mercury is fresh and the contact perfect) but strong ones are always produced, radiating from the other. If it be the negative pole which is made to touch, it amalgamates with the mercury, which remains bright, and the currents radiating from the positive are visible to the eye, and generally very powerful. On the other hand, if the positive pole be in contact, the oxidation of the metallic surface is usually so rapid as to prevent the currents becoming visible, but a momentary start of the surface

from the negative wire, the flattening of the globule, and the protuberances it throws out in pursuit of the oppositely electrified conductor, sufficiently indicate their existence under the crust of oxide. Where this oxidation however does not happen, or is prevented by the addition of a few drops of dilute nitric acid, the currents from the negative wire are equally evident with those from the positive, just mentioned.

19. These however are not the only effects produced by contact with the electrified wires. On breaking the contacts and completing the circuit in the liquid, the mercury is found for the most part to have acquired new properties, or lost some of its former ones. A globule of four or five hundred grains of pure mercury being introduced into a solution of sulphate of soda, the circuit was completed in the liquid with neither pole in contact. A current was produced from the negative pole. A momentary contact being made with that wire, and the circuit then completed as before in the liquid, a counter-current was produced from the positive pole, more confined in the sphere of its extent, but apparently more violent in its action than that from the negative. In consequence, the globule acquired the figure here annexed, having a blunt elongation at 2, the point nearest the negative pole, and a more pointed one at c, that next the positive, with a kind of shoulder at a b. The film of oxide produced at z was thus swept towards c, but never attained beyond

the zone a b, where it remained stationary and constant in quantity, being absorbed at the side next c as fast as it was produced at the other. Another short contact was now made with the negative wire, and, on breaking it, the currents from c were found to have increased both in strength and extent, while those from z were proportionally enfeebled, the zone of equilibrium a b being thus brought nearer to z. By another contact prolonged a few seconds, the negative currents were contracted within a very small space around z, and by prolonging the contact a little longer, its influence was totally destroyed, and a regular and violent circulation from + to established throughout the whole globule.