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same effects as an acid does on the latter. But Vasari says nothing of the kind.

After Tadda's death, the art of cutting porphyry came to Raphael Curradi, who communicated to Dominico Corsi this secret, which was afterwards employed by Cosimo Silvestrini1. I, however, agree in opinion with Winkelman and Fiorillo, our learned connoisseur in the arts, that the method of working porphyry was known in every age, even in the most barbarous, though artists, no doubt, preferred working on other stones which were less brittle and hard. We know however from the latest researches, that all the kinds of hardening water hitherto invented are in nothing superior to common water; and that in hardening more depends on the nature of the steel, or rather on the degree of heat, than on the water; although it is true that the workman does right when he adds to the water a thin cake of grease, or pours over it hot oil, through which the steel must necessarily pass before it enters the water, for by these means it is prevented from acquiring cracks and flaws.

The invention of converting bar iron into steel by dipping it into other fused iron, and suffering it to remain there several hours, is commonly ascribed to Reaumur. But this process is mentioned by Agricola, Imperati and others, as a thing well-known and practised in their time.

Pliny, Daimachus and other ancient writers mention various countries and places which, in their time, produced excellent steel. Among the dearest kinds were the ferrum Indicum and Sericum. The former appears to be the ferrum candidum, a hundred talents of which were given as a present to Alexander in India. Is it not probable that this was the excellent kind of steel still common in that country, and known under the name of wootz, some pieces of which were sent from Bombay in the year 1795 to the Royal Society of London? Its silver-coloured appearance when polished may have, perhaps, given occasion to the epithet of candidum.

1 Florillo Gesch. der Zeichnenden Künste, 8vo, i. p. 461.

2 Art de convertir le Fer en Acier, p. 245.

* Stephanus de Urbibus, under the word Aakedaiμwv, p. 413.

• Clemens Alexandr. in Pædagog. ii. p. 161, edit. Cologne, 1688, fol. says, speaking of luxury, "One can cut meat without having Indian iron."

The method of preparing it is still unknown, but it is supposed to be a kind of fused steel'. This however is a mere conjecture, unsupported by any proofs. At what time was damasked steel obtained from the Levant?

1 Philos. Transact. 1795, ii. p. 322.

2 [The manner in which iron ore is smelted and converted into wootz or Indian steel, by the natives at the present day, is probably the very same that was practised by them at the time of the invasion of Alexander; and it is a uniform process, from the Himalaya Mountains to Cape Comorin. The furnace or bloomery in which the ore is smelted, is from four to five feet high; it is somewhat pear-shaped, being about two feet wide at bottom and one foot at top; it is built entirely of clay, so that a couple of men may finish its erection in a few hours, and have it ready for use the next day. There is an opening in front about a foot or more in height, which is built up with clay at the commencement, and broken down at the end, of each smelting operation. The bellows are usually made of a goat's skin, which has been stripped from the animal without ripping open the part covering the belly. The apertures at the legs are tied up, and a nozzle of bamboo is fastened in the opening formed by the neck. The orifice of the tail is enlarged and distended by two slips of bamboo. These are grasped in the hand, and kept close together in making the stroke for the blast; in the returning stroke they are separated to admit the air. By working a bellows of this kind with each hand, making alternate strokes, a tolerably uniform blast is produced. The bamboo nozzles of the bellows are inserted into tubes of clay, which pass into the furnace at the bottom corners of the temporary wall in front. The furnace is filled with charcoal, and a lighted coal being introduced before the nozzles, the mass in the interior is soon kindled. As soon as this is accomplished, a small portion of the ore, previously moistened with water, to prevent it from running through the charcoal, but without any flux whatever, is laid on the top of the coals, and covered with charcoal to fill up the furnace. In this manner ore and fuel are supplied, and the bellows are urged for three or four hours, when the process is stopped, and the temporary wall in front broken down; the bloom is removed with a pair of tongs from the bottom of the furnace. In converting the iron into steel, the natives cut it into pieces to enable it to pack better in the crucible, which is formed of refractory clay, mixed with a large quantity of charred husk of rice. It is seldom charged with more than a pound of iron, which is put in with a proper weight of dried wood, chopped small, and both are covered with one or two green leaves; the proportions being in general ten parts of iron to one of wood and leaves. The mouth of the crucible is then stopped with a handful of tempered clay, rammed in very closely, to exclude the air. As soon as the clay plugs of the crucibles are dry, from twenty to twenty-four of them are built up in the form of an arch in a small blast furnace; they are kept covered with charcoal, and subjected to heat urged by a blast for about two hours and a half, when the process is considered to be complete. The crucibles being now taken out of the

[Three kinds of steel are now principally manufactured; bar or blistered steel, shear steel and cast steel.

The bar or blistered steel is made by the process of cementation: this consists in putting bars of the purest malleable iron alternately with layers of charcoal or soot into a proper furnace; the air being carefully excluded and the whole kept at a red heat for several days. By this process the carbon combines with the iron, altering its texture from fibrous to granular or crystalline, and rendering the surface blistered. The action of the carbon occasions fissures and cavities in the substance of the bars, rendering them unfit for tool-making, until they are condensed and rendered uniform by the operation of tilting, i. e. compression by a powerful hammer worked by machinery.

Shear steel is made by breaking up bars of blistered steel into lengths of about 18 inches, and binding four or six of them together with a steel rod, and then heating them to a full welding heat, the surface being covered with fine clay or sand to prevent oxidation. They are then drawn out into a bar, hammered, tilted and rolled. In this state it is susceptible of a much finer polish, and is also more tenacious and malleable, and fit for making strong springs, knives, &c.

Cast steel, which was first made by Mr. Huntsman at Attercliff, Sheffield, in 1770, is made by melting blistered steel, casting it into ingots and rolling it into bars. In this condition its texture is much more uniform, closer and finer grained. The different degrees of hardness required for steel are given by the process called tempering, which is effected by heating the steel up to a certain temperature, and then quenching it suddenly in cold water. Its hardness and brittleness are thus much increased, but it may be again softened by exposure to heat simply.]

furnace and allowed to cool, are broken, and the steel is found in the form of a cake, rounded by the bottom of the crucible.-Ure's Dictionary of Arts and Manufactures, art. STEEL.]

333

STAMPING-WORKS'.

In order to separate metallic ores from the barren rock or stones with which they occur, and to promote their fusion, it is necessary that the pieces of rock or stone should be reduced to small fragments by stamping them. For those ores which occur in a sandy form, this is unnecessary; and in regard to rich silver ore, which contains very little or no lead and other metals, this process might be hurtful; for with dry stamping a great deal would fly off in dust, and with wet stamping a considerable part would be washed away by the water.

However imperfect the knowledge of the ancients may have been in regard to the fusion of ores, they were acquainted with the benefit of stamping; but the means they employed for that purpose were the most inconvenient and expensive. They reduced the ore to coarse powder, by pounding it in mortars, and then ground it in hand-mills, like those used for corn, till it acquired such a degree of fineness that it could be easily washed. This is proved by the scanty information which we find in Diodorus Siculus and Agatharcides3, in regard to the gold mines of the Egyptians; in Hippocrates, respecting the smelting-works of the Greeks', and in Pliny in regard to the metallurgy of the Romans". Remains of such mortars and mills as were used by the ancients have been found in places where they carried on metallurgic operations; for instance, in Transylvania and the Pyrenees. The hand-mills had a resemblance to our mustardmills; and for washing the mud they employed a sieve, but in washing auriferous sand they made use of a raw hide. From the latter, Count von Veltheim has explained, in a very ingenious manner, the fable of the ancients concerning the ants which dug up gold'.

I shall refer those desirous of being acquainted with the nature of this labour, to Gatterer's Anleitung den Harz zu bereisen. Göttingen, 1785, 8vo. i. p. 101. [Figures of the stamping-works may be seen in Ure's Dictionary of Arts and Manufactures, pp. 818 and 1119.]

2 Diodor. iii. 13, p. 182.

3 Photii Bibl. p. 1342. Hippocrates de Victus Rat. lib. i. sect. 4. 5 Plin. xxxiii. 4, sect. 21. 6 Gensane Traité de la Fonte des Mines. Par. 1770, i. p. 14.

7 Yon d. goldgrabenden Ameisen u. Greiffen der Alten. Helmst. 1799. This dissertation may be found also in a valuable collection of different pieces by the same author, printed at Helmstadt, 1800.

Our works for pounding ore, at present, are stamping-mills, which consist of heavy stampers shod with iron. These stampers are put in motion by a cylinder furnished with cogs, which is driven by a water-wheel, and pound the ore in troughs lined with iron. When the ore subjected to this operation is poor, water is introduced into the troughs, which running through grates in the bottoms of them, carries with it the pounded matter into a gutter, where it becomes purified, and deposits the mud mixed with sand.

One might conjecture that this apparatus was invented soon after the invention of cylinders with cogs; but this was not the case, though I am not able to determine the antiquity of these cylinders. At any rate, it is certain that mortars and sieves were used in Germany throughout the whole of the fifteenth century; and in France, to which the art of mining was conveyed in general from that country at a late period, they were still employed about the year 1579'. In the oldest times men were not acquainted with the art of employing water at mines in so advantageous a manner as at present. The bellows were worked by men; and those aqueducts raised on posts, by which distant water may be made to act on machines, was not yet invented. On this account, remains of ore are found in places where the moderns, in consequence of that indispensable article water, would not be able to maintain metallurgic works. According to the researches which I have hitherto had an opportunity to make, our stampingmills were invented about the beginning of the sixteenth century, and, as appears, in Germany; but I cannot determine with certainty either the name of the inventor or his country. Those who established or introduced the first stamping-works in Saxony and the Harz are only mentioned; and these, as usual, have been considered as the inventors.

In the year 1519 the processes of sifting and wet-stamping

1 See François Garrault, Des Mines d'Argent trouvées en France, Paris 1579, where mention is made only of mortars, mills and sieves. This Garrault is the first French writer on mining. His work, which is scarce, was printed by Gobet in the first part of the Anciens Minéralogistes de France, Paris 1779, 8vo.

2 At the Nertschinsk works in Siberia, the machinery must be still driven by men or cattle, because all the dams and sluices are destroyed by the frost, and the water converted into ice. Some of the works there however have machinery driven by water during the few summer months.

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