Miracle Mongers and Their Methods/Chapter VII
THE spheroidal condition of liquids was covered by Leidenfrost, but M. Boutigny was the first to give this singular subject careful investigation. From time out of mind the test of letting a drop of water fall on the face of a hot flat-iron has been employed to discover whether it may safely be used. Everybody knows that if it is not too hot the water will spread over the surface and evaporate; but if it is too hot, the water will glance off without wetting the iron, and if this drop be allowed to fall on the hand it will be found that it is still cool. The fact is that the water never touches the hot iron at all, provided the heat is sufficiently intense, but assumes a slightly elliptical shape and is supported by a cushion of vapor. If, instead of a flat-iron, we use a concave metal disk about the size and shape of a watch crystal, some very interesting results may be obtained. If the temperature of the disk is at, or slightly above, the boiling point, water dropped on it from a medicine dropper will boil; but if the disk is heated to 340° F., the drop practically retains its roundness—becoming only slightly oblate—and does not boil. In fact the temperature never rises above 206° F., since the vapor is so rapidly evaporated from the surface of the drop that it forms the cushion just mentioned. By a careful manipulation of the dropper, the disk may be filled with water which, notwithstanding the intense heat, never reaches the boiling point. On the other hand, if boiling water be dropped on the superheated disk its temperature will immediately be reduced to six degrees below the boiling point; thus the hot metal really cools the water.
By taking advantage of the fact that different liquids assume a spheroidal form at widely different temperatures, one may obtain some startling results. For example, liquid sulphurous acid is so volatile as to have a temperature of only 13° F. when in that state, or 19° below the freezing point of water, so that if a little water be dropped into the acid, it will immediately freeze and the pellet of ice may be dropped into the hand from the still red-hot disk. Even mercury can be frozen in this way by a combination of chemicals.
Through the action of this principle it is possible to dip the hand for a short time into melted lead, or even into melted copper, the moisture of the skin supplying a vapor which prevents direct contact with the molten metal; no more than an endurable degree of heat reaches the hand while the moisture lasts, although the temperature of the fusing copper is 1996°. The natural moisture of the hand is usually sufficient for this result, but it is better to wipe the hand with a damp towel.
In David A. Wells' Things not Generally Known, New York, 1857, I find a translation of an article by M. Boutigny in The Comptes Rendus, in which he notes that "the portion of the hands which are not immersed in the fused metal, but are exposed to the action of the heat radiated from its surface, experience a painful sensation of heat." He adds that when the hand was dampened with ether "there was no sensation of heat, but, on the contrary, an agreeable feeling of coolness."
Beckmann, in his History of Inventions, Vol. II., page 122, says:
In the month of September, 1765, when I visited the copper works at Awested, one of the workmen, for a little drink money, took some of the melted copper in his hand, and after showing it to us, threw it against the wall. He then squeezed the fingers of his horny hand close together, put it for a few minutes under his armpit, to make it sweat, as he said; and, taking it again out, drew it over a ladle filled with melted copper, some of which he skimmed off, and moved his hand backwards and forwards, very quickly, by way of ostentation.
While I was viewing this performance, I remarked a smell like that of singed horn or leather, though his hand was not burnt.
The workmen at the Swedish melting-house showed the same thing to some travellers in the seventeenth century; for Regnard saw it in 1681, at the copper-works in Lapland.
My friend Quincy Kilby, of Brookline, Mass., saw the same stunt performed by workmen at the Meridan Brittania Company's plant. They told him that if the hand had been wet it would have been badly scalded.
Thus far our interest in heat-resistance has uncovered secrets of no very great practical value, however entertaining the uses to which we have seen them put. But not all the investigation of these principles has been dictated by considerations of curiosity and entertainment. As long ago as 1829, for instance, an English newspaper printed the following:
Proof against Fire—On Tuesday week an experiment was made in presence of a Committee of the Academy of Sciences at Paris, by M. Aldini, for the purpose of showing that he can secure the body against the action of flames so as to enable firemen to carry on their operations with safety. His experiment is stated to have given satisfaction. The pompiers were clothed in asbestos, over which was a network of iron. Some of them, it was stated, who wore double gloves of amianthus, held a red-hot bar during four minutes.
Sir David Brewster, in his Letters on Natural Magic, page 305, gives a more detailed account of Aldini, from which the natural deduction is that the Chevalier was a showman with an intellect fully up to the demands of his art. Sir David says:
In our own times the art of defending the hands and face, and indeed the whole body, from the action of heated iron and intense fire, has been applied to the nobler purpose of saving human life, and rescuing property from the flames. The revival and the improvement of this art we owe to the benevolence and the ingenuity of the Chevalier Aldini of Milan, who has travelled through all Europe to present this valuable gift to his species. Sir H. Davy had long ago shown that a safety lamp for illuminating mines, containing inflammable air, might be constructed of wire-gauze, alone, which prevented the flame within, however large or intense, from setting fire to the inflammable air without. This valuable property, which has been long in practical use, he ascribed to the conducting and radiating power of the wire-gauze, which carried off the heat of the flame, and deprived it of its power. The Chevalier Aldini conceived the idea of applying the same material, in combination with other badly conducting substances, as a protection against fire. The incombustible pieces of dress which he uses for the body, arms, and legs, are formed out of strong cloth, which has been steeped in a solution of alum, while those for the head, hands, and feet, are made of cloth of asbestos or amianthus. The head dress is a large cap which envelops the whole head down to the neck, having suitable perforations for the eyes, nose, and mouth. The stockings and cap are single, but the gloves are made of double amianthus cloth, to enable the fireman to take into his hand burning or red-hot bodies. The piece of ancient asbestos cloth preserved in the Vatican was formed, we believe, by mixing the asbestos with other fibrous substances; but M. Aldini has executed a piece of nearly the same size, 9 feet 5 inches long, and 5 feet 3 inches wide, which is much stronger than the ancient piece, and possesses superior qualities, in consequence of having been woven without the introduction of any foreign substance. In this manufacture the fibers are prevented from breaking by action of steam, the cloth is made loose in its fabric, and the threads are about the fiftieth of an inch in diameter.
The metallic dress which is superadded to these means of defence consists of five principal pieces, viz., a casque or cap, with a mask large enough to leave a proper space between it and the asbestos cap; a cuirass with its brassets; a piece of armour for the trunk and thighs; a pair of boots of double wire-gauze; and an oval shield 5 feet long by 2½ feet wide, made by stretching the wire-gauze over a slender frame of iron. All these pieces are made of iron wire-gauze, having the interval between its threads the twenty-fifth part of an inch.
In order to prove the efficacy of this apparatus, and inspire the firemen with confidence in its protection, he showed them that a finger first enveloped in asbestos, and then in a double case of wire-gauze, might be held a long time in the flame of a spirit-lamp or candle before the heat became inconvenient. A fireman having his hand within a double asbestos glove, and its palm protected by a piece of asbestos cloth, seized with impunity a large piece of red hot iron, carried it deliberately to the distance of 150 feet, inflamed straw with it, and brought it back again to the furnace. On other occasions the fireman handled blazing wood and burning substances, and walked during five minutes upon an iron grating placed over flaming fagots.
In order to show how the head, eyes, and lungs are protected, the fireman put on the asbestos and wire-gauze cap, and the cuirass, and held the shield before his breast. A fire of shavings was then lighted, and kept burning in a large raised chafing-dish; the fireman plunged his head into the middle of the flames with his face to the fuel, and in that position went several times round the chafing-dish for a period longer than a minute. In a subsequent trial, at Paris, a fireman placed his head in the middle of a large brazier filled with flaming hay and wood, and resisted the action of the fire during five or six minutes and even ten minutes.
In the experiments which were made at Paris in the presence of a committee of the Academy of Sciences, two parallel rows of straw and brushwood supported by iron wires, were formed at the distance of 3 feet from each other, and extended 30 feet in length. When this combustible mass was set on fire, it was necessary to stand at a distance of 8 or 10 yards to avoid the heat. The flames from both the rows seemed to fill up the whole space between them, and rose to the height of 9 or 10 feet. At this moment six firemen, clothed in the incombustible dresses, and marching at a slow pace behind each other, repeatedly passed through the whole length between the two rows of flame, which were constantly fed with additional combustibles. One of the firemen carried on his back a child eight years old, in a wicker-basket covered with metallic gauze, and the child had no other dress than a cap made of amianthine cloth.
In February, 1829, a still more striking experiment was made in the yard of the barracks of St. Gervais. Two towers were erected two stories high, and were surrounded with heaps of inflamed materials, consisting of fagots and straw. The firemen braved the danger with impunity. In opposition to the advice of M. Aldini, one of them, with the basket and child, rushed into a narrow place, where the flames were raging 8 yards high. The violence of the fire was so great that he could not be seen, while a thick black smoke spread around, throwing out a heat which was unsupportable by spectators. The fireman remained so long invisible that serious doubts were entertained of his safety. He at length, however, issued from the fiery gulf uninjured, and proud of having succeeded in braving so great a danger.
It is a remarkable result of these experiments, that the firemen are able to breathe without difficulty in the middle of the flames. This effect is owing not only to the heat being intercepted by the wire-gauze as it passes to the lungs, in consequence of which its temperature becomes supportable, but also to the singular power which the body possesses of resisting great heats, and of breathing air of high temperatures.
A series of curious experiments were made on this subject by M. Tillet, in France, and by Dr. Fordyce and Sir Charles Blagden, in England. Sir Joseph Banks, Dr. Solander, and Sir Charles Blagden entered a room in which the air had a temperature of 198° Fahr., and remained ten minutes; but as the thermometer sunk very rapidly, they resolved to enter the room singly. Dr. Solander went in alone and found the heat 210°, and Sir Joseph entered when the heat was 211°. Though exposed to such an elevated temperature, their bodies preserved their natural degree of heat. Whenever they breathed upon a thermometer it sunk several degrees; every expiration, particularly if strongly made, gave a pleasant impression of coolness to their nostrils, and their cold breath cooled their fingers whenever it reached them. On touching his side, Sir Charles Blagden found it cold like a corpse, and yet the heat of his body under his tongue was 98°. Hence they concluded that the human body possesses the power of destroying a certain degree of heat when communicated with a certain degree of quickness. This power, however, varies greatly in different media. The same person who experienced no inconvenience from air heated to 211°, could just bear rectified spirits of wine at 130°, cooling oil at 129°, cooling water at 123°, and cooling quicksilver at 118°. A familiar instance of this occurred in the heated room. All the pieces of metal there, even their watch-chains, felt so hot that they could scarcely bear to touch them for a moment, while the air from which the metal had derived all its heat was only unpleasant. M. Duhamel and Tillet observed, at Rochefoucault in France, that the girls who were accustomed to attend ovens in a bakehouse, were capable of enduring for ten minutes a temperature of 270°.
The same gentleman who performed the experiments above described ventured to expose themselves to still higher temperatures. Sir Charles Blagden went into a room when the heat was 1° or 2° above 260°, and remained eight minutes in this situation, frequently walking about to all the different parts of the room, but standing still most of the time in the coolest spot, where the heat was above 240°. The air, though very hot, gave no pain, and Sir Charles and all the other gentlemen were of opinion that they could support a much greater heat. During seven minutes Sir C. Blagden's breathing continued perfectly good, but after that time he felt an oppression in his lungs, with a sense of anxiety, which induced him to leave the room. His pulse was then 144, double its ordinary quickness. In order to prove that there was no mistake respecting the degree of heat indicated by the thermometer, and that the air which they breathed was capable of producing all the well-known effects of such a heat on inanimate matter, they placed some eggs and a beef-steak upon a tin frame near the thermometer, but more distant from the furnace than from the wall of the room. In the space of twenty minutes the eggs were roasted quite hard, and in forty-seven minutes the steak was not only dressed, but almost dry. Another beef-steak, similarly placed, was rather overdone in thirty-three minutes. In the evening, when the heat was still more elevated, a third beef-steak was laid in the same place, and as they had noticed that the effect of the hot air was greatly increased by putting it in motion, they blew upon the steak with a pair of bellows, and thus hastened the dressing of it to such a degree, that the greatest portion of it was found to be pretty well done in thirteen minutes.
Our distinguished countryman, Sir F. Chantrey, has very recently exposed himself to a temperature still higher than any which we have mentioned. The furnace which he employs for drying his moulds is about 14 feet long, 12 feet high, and 12 feet broad. When it is raised to its highest temperature, with the doors closed, the thermometer stands at 350°, and the iron floor is red hot. The workmen often enter it at a temperature of 340°, walking over the iron floor with wooden clogs, which are of course charred on the surface. On one occasion Sir F. Chantrey, accompanied by five or six of his friends, entered the furnace, and, after remaining two minutes, they brought out a thermometer which stood at 320°. Some of the party experienced sharp pains in the tips of their ears, and in the septum of the nose, while others felt a pain in their eyes.