The Book of Curiosities

by John Platts

The solar rays received on a circular surface of two feet eight inches and a half, when concentrated within the diameter of an inch, will be 105,626 times its intensity, or this number of times greater than the heat of the sun as it is experienced on the surface of the earth. We will suppose, that as the heat of the air, in ordinary summer weather, is 65 degrees, and in sultry weather is 75 degrees, the average of which is 70 degrees, and that we take this as the average effect, the accumulated power of the lens, on the supposition of an uniform heat over the whole surface of the focus, will be equal to 73,938 degrees. It must be recollected, by those who have an opportunity of examining the effects of this lens, that the external part of the focal light was less intense than that part which was near the centre of it; or rather, that the effect was very much accumulated in the centre; but as it is possible that the refraction of the light and of the caloric fluid may not take place in the same angles, we think it safest to consider it as of uniform effect, and alter deducting one fourth part thereof as a compensation, there remains 5545 as the expression of its power. As the application of the second lens reduced the diameter of the focus to half an inch, the effect, without allowing for the reduction of its power, would be equal to 221,816 degrees; but deducting one-fourth for the second transmission, there remains 166,362 degrees, as the expression of its power.

Mr. Parker further informs us, that a diamond, weighing ten grains, exposed to this lens for thirty minutes, was reduced to six grains; during which operation it opened and foliated like the leaves of a flower, which emitted whitish fumes, and when closed again, bore a polish, and retained its form. Gold remained in its metallic state without apparent diminution, notwithstanding an exposure at intervals of many hours: but what is remarkable, the rest, or cupel, which was composed of bone-ash, was tinctured with a beautiful pink colour.

The experiments on platina evince that the specimens were in different states of approach to a complete metallic form; several of them threw off their parts in sparks, which in most instances were metallic. Copper, after three minutes’ exposure, was not found to have lost in weight.

What is remarkable with regard to experiments on iron, is, that the lower part, i. e. that part in contact with the charcoal, was first melted, when that part which was exposed to the focus remained unfused; an evidence of the effect of flux on this metal.

Several of the semi-crystalline substances, exposed to the focal heat, exhibited symptoms of fusion; such as the agate, oriental flint, cornelian, and jasper: but as the probability is, that these substances were not capable of complete vitrification, it is enough that they were rendered externally of a glassy form. Garnet completely fused on black lead in 120 seconds, lost a quarter of a grain, became darker in colour, and was attracted by the magnet. Ten cut garnets taken from a bracelet began to run the one into the other in a few seconds, and at last formed into one globular garnet. The clay used by Mr. Wedgwood to make his pyrometric test, run in a few seconds into a white enamel. Seven other kinds of clay, sent by Mr. Wedgwood, were all vitrified. Several experiments were made on limestone, some of which were vitrified, but all of which were agglutinated; it is, however, suspected that some extraneous substance must have been intermixed. A globule produced from one of the specimens, on being put into the mouth, flew into a thousand pieces, occasioned, it is presumed, by the moisture.

A subscription was proposed for raising the sum of seven hundred guineas, towards indemnifying the charges of the inventor, and retaining the very curious and useful machine above described in our own country; but from the failure or the subscription, and some other concurring circumstances, Mr. Parker was induced to dispose of it to Capt. Mackintosh, who accompanied Lord Macartney in the embassy to China: and it was left, much to the regret of philosophers in Europe, at Pekin; where it remains in the hands of persons, who most probably know neither its value nor use.

Ductility of Glass.—We all know, that when glass is well penetrated with the heat of the fire, the workmen can figure and manage it like soft wax; but, what is most remarkable, it may be drawn, or spun out, into threads exceedingly long and fine. Our ordinary spinners do not form their threads of silk, flax, or the like, with half the ease and expedition the glass-spinners do threads of this brittle matter. We have some of them used in plumes for children’s heads, and divers other works, much finer than any hair, and which bend and wave, like hair, with every wind. Nothing is more simple and easy than the method of making them. There are two workmen employed: the first holds one end of a piece of glass over the flame of a lamp; and when the heat has softened it, a second operator applies a glass hook to the metal thus in fusion, and, withdrawing the hook again, it brings with it a thread of glass, which still adheres to the mass; then, fitting his hook on the circumference of a wheel about two feet and a half in diameter, he turns the wheel as fast as he pleases, which, drawing out the thread, winds it on its run, till, after a certain number of revolutions, it is covered with a skein of glass-thread. The mass in fusion over the lamp diminishes insensibly, being wound out like a clue of silk upon the wheel; and the parts cooling as they recede from the flame, become more coherent to those next to them, and this by many degrees: the parts nearest the fire are always the least coherent, and, of consequence, must give way to the effort the rest make to draw them towards the wheel. The circumference of these threads is usually a flat oval, being three or four times as broad as thick: some of them seem scarcely bigger than the thread of a silkworm, and are surprisingly flexible. If the two ends of such threads are knotted together, they may be drawn and bent, till the aperture, or space in the middle of the knot, does not exceed one-fourth of a line, or one forty-eighth of an inch in diameter. Hence M. Reaumur maintains, that the flexibility of glass increases in proportion to the fineness of the threads; and that, probably, had we but the art of drawing threads as fine as a spider’s web, we might weave stuffs and cloths of them for wear. Accordingly, he made some experiments this way; and found that he could make threads fine enough, viz. as fine, in his judgment, as spider’s thread, but not long enough for the purposes of any manufacture.

Remarkable Ductility and Extensibility of Gold.—Gold is the most ductile, as well as the most malleable, of all metals. According to Cronstedt, one grain of it may be stretched out so as to cover 98 Swedish ells, equal to 63.66 English yards of silver wire; but Wallerius asserts, that a grain may be stretched out in such a manner, as to cover 500 ells of wire. At any rate, the extension is prodigious; for, according to the least of the calculations, the millionth part of a grain of gold may be made visible to the naked eye. Nor is its malleability inferior to its ductility. Boyle, quoted by Apligny, in his treatise on Colours, says, that one grain and a half of gold may be beaten into 50 leaves of an inch square, which, if intersected by parallel lines drawn at right angles to each other, and distant only the hundredth part of an inch from each other, will produce twenty-five millions of little squares, each very easily discernible by the naked eye. Mr. Magellan tells us, that its surface may be extended by the hammer 159,092 times. “I am informed, (says he) by an intelligent goldbeater in England, that the finest gold leaf is that made in new skins, and must have an alloy of three grains of copper to the ounce of pure gold, or else it would be too soft to pass over the irregularities of the skins. He affirms, that 80 books, or 2000 leaves of gold, each leaf containing 10.89 square inches, weigh less than 384 grains. Each book, therefore, of 25 leaves, or 272.25 inches, weighs less than 4.8 grains; so that each grain of the metal will produce about 57 square inches of gold leaf.” From further calculation it appears, that the thickness of these leaves is less than the 282,000th part of an inch; and that 16 ounces of gold would be sufficient to gild a silver wire, equal in length to the whole circumference of the globe we inhabit!

Pin-making.—Though pins are apparently simple, their manufacture is not a little curious and complex. When the brass wire, of which the pins are formed, is first received at the manufactory, it is generally too thick for the purpose of being cut into pins. The first operation, therefore, is that of winding it off from one wheel to another with great velocity, and causing it to pass between the two, through a circle in a piece of iron of smaller diameter. The wire being thus reduced to its proper dimensions, is straightened by drawing it between iron pins, fixed in a board in a zigzag manner, but so as to leave a straight line between them: afterwards it is cut into lengths of three or four yards, and then into smaller ones, every length being sufficient to make six pins. Each end of these is ground to a point, which was performed, (where these observations were made,) by boys, who sat each with two small grinding-stones before him, turned by a wheel. Taking up a handful, he applied the ends to the coarsest of the two stones, being careful at the same time to keep each piece moving round between his fingers, so that the points may not become flat: he then gives them a smoother and sharper point by applying them to the other stone, and by that means a lad of twelve or fourteen years of age, is able to point about sixteen thousand pins in an hour. When the wire is thus pointed, a pin is taken off at each end, and this is repeated till it is cut into six pieces. The next operation is, that of forming the heads, or, as they term it, head-spinning, which is done by means of a spinning-wheel, one piece of wire being thus with astonishing rapidity wound round another, and the interior one being drawn out, leaves a hollow tube between the circumvolutions: it is then cut with shears, every two circumvolutions, or turns of the wire, forming one head; these are softened by throwing them into iron pans, and placing them in a furnace till they are red hot. As soon as they are cold, they are distributed to children, who sit with hammers and anvils before them, and catching one at the extremity, they apply them immediately to the anvil and hammer, and by a motion or two of the foot, the top and the head are fixed together in much less time than it can be described, and with a dexterity only to be acquired by practice. The pin is now finished as to its form, but still it is merely brass; it is therefore thrown into a copper containing a solution of tin and the lees of wine. Here it remains for some time, and, when taken out, assumes a white, though dull appearance: in order therefore to give it a polish, it is put into a tub containing a quantity of bran, which is set in motion by turning a shaft that runs through its centre, and thus, by means of friction, it becomes perfectly bright. The pin being complete, nothing remains but to separate it from the bran, which is perfectly similar to the winnowing of corn, the bran flying off, and leaving the pin behind it for immediate sale.