were various fluids and mixtures which communicate to steel different degrees of hardness, and every artist thought he knew a peculiar hardening kind of water, the preparation of which he kept a secret. This notion is by some still maintained'; because there are often found stones cut by the ancients, which the moderns, on account of their hardness, as is believed, have seldom ventured to touch. Of this kind is the hardest porphyry. There are people who still endeavour to find out that hardening kind of water, in which the ancients prepared their tools for cutting such stones. According to Vasari, that water was actually discovered by the archduke Cosmo, in the year 1555. Among a large collection of stones he had a block of porphyry, from which he wished a bason to be made for a well, but was told by the most experienced artists that it was impossible. On this, says Vasari, in order to render the work possible, he prepared from certain herbs, which he does not name, a water wherein the red-hot tools were quenched, and by these means so hardened, that they were capable of cutting porphyry. With tools tempered in this cutting_porphyry. manner the artist Francesco del Tadda not only made the required bason, but various other curious articles 3.

Winkelman, therefore, does injustice to Vasari when he says, "Vasari, in pretending that Cosmo archduke of Tuscany discovered a water for making porphyry soft, betrays childish credulity." On the contrary, he very properly asserts that there is no water of such a quality as to soften porphyry; though Porta and many old writers imagined that they were acquainted with one capable of producing on that stone, which they considered as a species of marble, the

1 [There can be no question that the hardening or tempering effect produced by the sudden immersion of heated steel in fluids has no relation to the quality of the fluid, save as regards its conducting power of heat. The more suddenly the heat is abstracted from the metal, the greater is the amount of hardness and brittleness. Mercury has been found superior to any other fluid for this purpose, undoubtedly because it is so good a conductor of heat.]

2 Le Vite de Pittori. Bologna, 1681, 4to, i. p. 11.

3 Some account of this artist is given in J. C. Bulengeri de Pictura, lib. ii. cap. 7, in Gronovii Thesaurus Antiq. Græc. ix. p. 875. On the other hand, Sturm says, in that part of the Ritterplatzes which relates to architecture, p. 18: "An archduke at Florence discovered again the art of working porphyry, but suffered it to die with him in the year 1556."

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 2. 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.

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

4 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 Agatharcides, 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 gold7.

1 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.

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

7 Von 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.