DUCTILITY. A property of certain bodies, in consequence of which they can be drawn out at length without suf fering any interruption of the continuity of their constituent particles. The term ductility is frequently confounded with malleability, or that property of bodies through which different forms can be given to them by pressure or percussion. In general ductility depends, in a greater or less degree, on the temperature. Some bodies—wax for example—are rendered ductile by a small degree of heat ; while glass requires a violent heat before it acquires ductility. Some of the metals for example, gold, silver, lead, &c.— are ductile under all known tempera tures.
"The ductility of some metals far ex ceeds that of any other substance. The goldbeaters begin their operations with a riband an inch broad and 150 inches long, which had been reduced, by passing it through rollers, to about the 800th part of an inch in thickness. The riband is cut into squares, which are disposed between leaves of vellum, and beat by a heavy hammer till they acquire a breadth of about three inches, and are thus ex tended to ten times their former sur face. These are again quartered and placed between the folds of goldbeater's skin. and stretched out by the operation of a lighter hammer to the breadth of five inches. The same process is re peated, sometimes more than once, by a succession of lighter hammers ; so that 876 grains of gold are thus finally ex tended into 2000 leaves of 3.8 inches square, making in all 80 books, contain ing each of them 25 leaves. The metal is consequently reduced to the thinness of the 282,000th part of an inch, and every leaf weighs rather less than the fifth part of a grain. A particle of gold, not exceeding the 500,000th part of a grain, is hence distinctly visible to the naked eye.
" It has been asserted that wires of pure gold can be drawn of only the 4000th part of an inch in diameter ; but Dr.
Wollaston, by an ingenious procedure, has lately advanced much farther. Tak ing a short cylinder of silver, about the third part of an inch in diameter, he a fine hole through its axis, and inserted a wire of platinum only the 100th part of an inch thick. This silver mould was now drawn through the suc cessive holes of a steel plate, till its di ameter was brought to near the 1500th part of an inch and consequently the internal being diminished in the same proportion, was reduced to between the 4000th and 5000th part of an inch. The compound wire was then dipped in warm nitric acid, which dissolved the silver, and left untouched its core, or the wire of platinum. By passing the in crusted platinum through a greater num ber of holes wires still finer were ob tained, some of them only the 80,000th part of an inch in diameter. The te nacity of the metal, before reaching this limit, was even considerable ; a platinum wire, of the 18,000th part of an inch in diameter, supporting the weight of a grain and a third." Glass, when well softened by the fire, becomes as ductile as soft wax, and may be spun out into threads of greater fine ness than any hair, and which bend and wave like hair in the wind. The method of producing these threads is exceedingly easy. Two workmen are employed ; the first holds the glass over the flame of a lamp ; the second applies a hook to the metal in fusion, which, when drawn back, brings with it a thread of glass, still adhering to the mass ; the hook is then fitted on the circumference of a wheel, which, being turned round, draws out the thread, and winds it about its rim. Some of these threads are scarcely larger than that of a silkworm, and are surprisingly flexible.