CECILIA. Our conversation upon coins, has led me to consider that I am extremely ignorant of the nature and properties of metals. I wish I may be obliged with hearing something relative to them this evening.

MRS. HARCOURT. The subject you have chosen is extensive, and is connected with many branches of the arts; but I am willing to oblige you, as far as our time will allow. I suppose you are acquainted with the names. of the principal metals.

CECILIA. Gold, silver, quicksilver, copper, iron, tin, and lead, have been known from very high antiquity; and I am anxious to obtain more particular information respecting them.

MR. HARCOURT. Gold is the most valu

able; therefore, we will begin with it. The qualities which give it this superiority, are, ductility, heaviness, and beauty, in which it excels all others. It possesses, in common with other metals, the properties of being fused or melted by fire, and of distending or spreading out under the hammer.

SOPHIA. I have heard that gold is the heaviest of all bodies.

MR. HARCOURT. It was believed to be so, till the discovery of a metallic substance, called platina, which is as ponderous as gold itself, and sometimes even much more so. Gold is more than nineteen times as heavy as its own bulk of water; silver nearly eleven times; copper between eight and nine times; iron something more than seven, and less than eight times; lead eleven; and tin but seven. By comparing gold with the rest, you will be enabled to judge of its superior weight. The next quality I shall remark in this valuable metal, is the cohesion of the particles which compose it: so firmly do they adhere to each other, that it is extremely difficult to separate them. A wire of gold, one-tenth of an inch

[blocks in formation]

in diameter, will support a weight of five hundred pounds, without breaking. From this property arises another, which is its ductility, or capacity of being beaten, pressed, drawn, or stretched out to a surprising degree of thinness.

AUGUSTA. Is not the leaf-gold we used to buy for gilding pictures, beaten thus?

MRS. HARCOURT. Yes: the expansion of the metal in that process is almost beyond imagination. M. Reaumur asserts, that, in an experiment he made, one grain of gold was extended to rather more than forty-two square inches of leaf gold; and that an ounce of gold, which, in form of a cube, is not half an inch, either high, broad, or long, is beat under the hammer, into a surface of one hundred and fifty square feet.

HENRY. How astonishing! Do tell us how this wonderful operation is performed.

MR. HARCOURT. A block of black marble, of several hundred pounds weight, with a square surface, about nine inches each way, fixed in a wooden frame, serves for a table to beat the gold upon. Three of its sides are

guarded by a high ledge, and the front, which is open, has a leather flap fastened to it. This the gold-beater uses as an apron, to preserve the fragments of gold that fall off, For this purpose the purest gold is melted in a crucible into ingots, or pieces of six or eight inches long, and three quarters of an inch wide. This bar of gold is made red hot, and forged on an anvil into a long plate, which is further extended, by being passed repeatedly between polished steel rollers, till it becomes a ribbon as thin as paper. This is divided into equal pieces, which are again forged till they are an inch square. These squares are interlaid with leaves of vellum, three or four inches square: both are confined tight with cases of parchment, placed in contrary directions. The whole is then beaten with the heaviest hammer, till the gold is stretched to the extent of the vellum. In this state the sheets of gold are then taken out, and cut in four with a steel knife. These pieces are now intersected with the leaves of the fine skin of an ox-gut, properly prepared, five inches square. They are again beaten till they are

extended to the size of the pieces of skin. The same operations of dividing and beating are repeated the third time. Nothing remains to finish the process, but cutting the edges even, with a machine adapted to the purpose, and fixing the leaves of gold in books, the paper of which is well smoothed, and rubbed with red bole, that it may not stick to them.

SOPHIA. I suppose the gold-beater's skin, which is used for healing cuts and scratches, is the same which you mention to be prepared from the gut of an ox.

MR. HARCOURT. You conjecture rightly. MRS. HARCOURT. Although the distension of gold is so great under the hammer, it is vastly exceeded by the art of the wire-drawer.

AUGUSTA. I should have thought that impossible.

MRS. HARCOURT. There are gold leaves not thicker, in some parts, than the three hundred and sixty thousandth part of an inch; but that is inconsiderable, when compared with the extreme thinness of gold spun for laces and embroidery. Gold thread is

« VorigeDoorgaan »