THE SPHEROIDAL CONDITION OF LIQUIDS.--WHY THE HAND MAY BE DIPPED IN
MOLTEN METALS.--PRINCIPLES OF HEAT-RESISTANCE PUT TO PRACTICAL USES:
ALDINI, 1829.--IN EARLY FIRE-FIGHTING. TEMPERATURES THE BODY CAN
ENDURE.
The spheroidal condition of liquids was discovered 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 degrees F., the drop practically retains its
roundness--becoming only slightly oblate--and does not boil. In fact
the temperature never rises above 206 degrees 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 degrees F. when in that state, or
19 degrees 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 degrees. 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
2 1/2 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 degrees 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 degrees, and Sir Joseph entered when the heat was 211 degrees.
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
degrees. 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 degrees, could just bear rectified spirits of wine at 130
degrees, cooling oil at 129 degrees, cooling water at 123 degrees, and
cooling quicksilver at 118 degrees. 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 degrees.
The same gentleman who performed the experiments above described
ventured to expose themselves to still higher temperatures. Sir
Charles Blagden went into a room where the heat was 1 degree or 2
degrees above 260 degrees, 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 degrees. 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 degrees, and the iron floor is red hot. The workmen often enter
it at a temperature of 340 degrees, 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 degrees. 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.