WIRE-DRAWING

( Tréfilerie , Fr.; Draht-ziehen , Drahtzug , Germ.) When an oblong lump of metal is forced through a series of progre ively diminishing apertures in a steel plate, so as to a ume in its cro section the form and dimensions of the last hole, and to be augmented in length at the expense of its thickne , it is said to be wire-drawn. The piece of steel called the draw-plate is pierced with a regular gradation of holes, from the largest to the smallest; and the machine for overcoming the lateral adhesion of the metallic particles to one another, is called the draw-bench . The pincers which lay hold of the extremity of the wire, to pull it through the succe ive holes, are adapted to bite it firmly, by having the inside of the jaws, cut like a file. For drawing thick rods of gilt silver down into stout wire, the hydraulic pre has been had recourse to with advantage. IMG:4147767755307473660_illo1305.png:Wire drawing bench Fig. 1202. represents a convenient form of the draw-bench, where the power is applied by a toothed wheel, pinion, and rack-work, moved by the hands of one or two men working at a winch; the motion being so regulated by a fly-wheel, that it does not proceed in fits and starts, and cause inequalities in the wire. The metal requires to be annealed, now and then, between succe ive drawings, otherwise it would become too hard and brittle for further extension. The reel upon which it is wound is sometimes mounted in a cistern of sour small beer, for the purpose of clearing off, or loosening at least, any crust of oxide formed in the annealing, before the wire enters the draw-plate. When, for very accurate purposes of science or the arts, a considerable length of uniform wire is to be drawn, a plate with one or more jewelled holes, that is, filled with one or more perforated rubies, sapphires, or chrysolites, can alone be trusted to, because the holes even in the best steel become rapidly wider by the abrasion. Through a hole in a ruby 0·0033 of an inch in diameter, a silver wire 170 miles long has been drawn, which po e ed at the end, the very same section as at the beginning; a result determined by weighing portions of equal length, as also by measuring it with a micrometer. The hole in an ordinary draw-plate of soft steel becomes so wide, by drawing 14,000 fathoms of bra wire, that it requires to be narrowed before the original sized wire can be again obtained. Wire, by being diminished one-half, one-third, one-fourth, ., in diameter, is augmented in length respectively, four, nine, sixteen times, . The speed with which it may be prudently drawn out, depends upon the ductility and tenacity of the metal; but may be always increased the more the wire becomes attenuated, because its particles progre ively a ume more and more of the filamentous form, and accommodate themselves more readily to the extending force. Iron and bra wires, of 0·3 inch in diameter, bear drawing at the rate of from 12 to 15 inches per second; but when of 0·025 ( 1 ⁄ 40 ) of an inch, at the rate of from 40 to 45 inches in the same time. Finer silver and copper wire may be extended from 60 to 70 inches per second. By enclosing a wire of platinum within one of silver ten times thicker, and drawing down the compound wire till it be 1 ⁄ 300 of an inch, a wire of platinum of 1 ⁄ 3000 of an inch, will exist in its centre, which may be obtained apart, by di olving the silver away in nitric acid. This pretty experiment was first made by Dr. Wollaston. The French draw-plates are so much esteemed, that one of the best of them used to be sold in this country, during the late war, for its weight in silver. The holes are formed with a steel punch; being made large on that side where the wire enters, and diminishing with a regular taper to the other side. In the act of drawing, they must be well supplied with grease for the larger kinds of wire, and with wax for the smaller. WOAD ( Vouëde , Pastel , Fr.; Waid , Germ; Is at is tinct or i a , Linn.); the glastum of the antient Gauls and Germans; is an herbaceous plant which was formerly much cultivated, as affording a permanent blue dye, but it has been in modern times well nigh superseded by indigo . Pliny says, “A certain plant which resembles plant a go , called glastum , is employed by the women and girls in Great Britain for dyeing their bodies all over, when they a ist at certain religious ceremonies; they have then the colour of Ethiopians.”— Hist. Nat. cap. xxii. § 2. When the arts, which had perished with the Roman empire, were revived, in the middle ages, woad began to be generally used for dyeing blue, and became an object of most extensive cultivation in many countries of Europe. The environs of Toulouse and Mirepoix, in Upper Langue doc, produced annually 40,000,000 pounds of the prepared woad, or pastel, of which 200,000 bales were consumed at Bordeaux. Beruni, a rich manufacturer of this drug, became surety for the payment of the ransom of his king, Francis I., then the prisoner of Charles V. in Spain. The leaves of woad are fermented in heaps, to destroy certain vegetable principles injurious to the beauty of the dye, as also to elaborate the indigo fer ous matter present, before they are brought into the market; but they should be carefully watched during this proce . Whenever the leaves have arrived at maturity, a point judged of very differently in different countries, they are stripped off the plant, a cropping which is repeated as often as they shoot, being three or four times in Germany, and eight or ten times in Italy. The leaves are dried as quickly as po ible, but not so much as to become black; and they are ground before they get quite dry. The resulting paste is laid upon a sloping pavement, with gutters for conducting the juice which exudes into a tank; the heap being tramped from time to time, to promote the discharge of the juice. The woad ferments, swells, and cracks in many places, which fi ures must be closed; the whole being occasionally watered. The fermentation is continued for twenty or thirty days, in cold weather; and if the leaves have been gathered dry, as in Italy, for four months. When the fermented heap has become moderately dry, it is ground again, and put up in cakes of from one to three pounds; which are then fully dried, and packed up in bundles for the market. Many dyers subject the pastel to a second fermentation. 1,600 square toises (fathoms) of land afford in two cuttings at least 19,000 pounds of leaves, of which weight four-fifths are lost in the fermentation, leaving 3,880 pounds of pastel, in loaves or cakes. When good, it has rather a yellow, or greenish-yellow, than a blue colour; it is light, and slightly humid; it gives to paper a pale-green trace; and improves by age, in consequence of an obscure fermentation; for if kept four years, it dyes twice as much as after two years. According to Hellot, 4 pounds of Guatimala indigo produce the same effect as 210 pounds of the pastel of Albi. At Quins, in Piedmont, the dyers estimate that 6 pounds of indigo are equivalent to 300 of pastel; but Chaptal thinks the indigo underrated. Pastel will dye blue of itself, but it is commonly employed as a fermentative addition to the proper blue vat, as described under Indigo . Fresh woad, analyzed by Chevreul, afforded, in 100 parts, 65·4 of juice. After being steeped in water, the remaining ma yielded, on expre ion, 29·65 of liquid; being in whole, 95·05 parts, leaving 4·95 of ligneous fibre. The juice, by filtration, gave 1·95 of green fecula. 100 parts of fresh woad, when dried, are reduced to 13·76 parts. Alcohol, boiled upon dry woad, deposits, after cooling, indigo in microscopic needles; but these cannot be separated from the vegetable albumine, which retains a greenish-gray colour.