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called forth loud and continued applause, is this:--sulphurous acid has the property of boiling water when it is at a temperature below the freezing point; and, when poured into the heated vessel, the suddenness of the evaporation occasions a degree of cold sufficient to freeze water.
Liquid carbonic acid takes a high position for its freezing qualities. Mr. Adams, of Kensington, manufactures this curious liquid as an article of commerce, and has, occasionally, as much as nine gallons of it in store. In drawing it from its powerful reservoirs, it evaporates so rapidly as to freeze, and it is then a light porous mass, like snow. If a small quantity of this is drenched with ether, the degree of cold produced is even more intolerable to the touch than boiling water; a drop or two of the mixture producing blisters, just as if the skin had been burned! Mr. Adams states that, in eight minutes he has frozen a mass of mercury weighing ten pounds.
In one department of knowledge--that of vapours and gases--on which chemistry casts so much light, we discover many remarkable phenomena. Few persons have resided, for example, in the fenny and swampy districts of our island, without seeing, at least occasionally, the ignis fatuus, Will-o'-the-wisp, or Jack-o'-lantern, hovering a few feet above the surface of stagnant water.
"Wild fires dancing o'er the heath,"
may be observed, indeed, at almost all times of the year, but it is chiefly in autumn, and particularly in November, that they flit in mazy circles and irregular evolutions; sometimes at the edge of a morass, over the tops of withered sedges, reeds, and brushwood; and, at others, over palings and hedgerows, or the still surface of the oozy bog.
It has been argued by some, that they are effects produced by luminous insects, as the glow-worm, the gnat, and the mole-cricket. But this theory is very unsatisfactory, and the cause which is now generally acknowledged to be the real one, is far more natural. There is a substance readily obtained, but of very offensive odour, called phosphoret of lime; and, if a piece of this be taken and dropped into a pool of water, little flames will be seen on its surface. These arise from the power of the substance to decompose water, in consequence of which, the hydrogen ascends to the surface, and ignites on coming in contact with the air.
Dr. Weissenborn has given the following interesting statements:--"In the year 1818, I was fortunate enough to get a fine view of the ignes fatui operating on an extensive scale. I was then at Schnepfenthal, in the duchy of Gotha; and in a clear November night, between eleven and twelve o'clock, when I had just undressed, the bright moonshine allured me to the window, to survey the expanse of boggy meadows, which spread two or three English miles in length, a quarter-of-a-mile from the foot of the hillock on which the house in which I then was, is standing. Through the first third of the meadows there was a winding rivulet, of the breadth of seven or eight feet, which then turns off into an artificial bed, whilst the old bed continues in the direction of the meadows, which are bounded on one side by a range of brushwood, and on the other by cultivated grounds, with marshy dells here and there. My intimate acquaintance with the locality, together with the bright moonshine, enabled me to discover every object round the meadow-ground, sufficiently well to judge of the position and direction of the luminous phenomena, the display of which I saw as soon as I had posted myself at the window. I perceived a number of reddish yellow flames on different parts of the expanse of almost level ground. I descried, perhaps, no more than six at a time, but dying away and appearing in other places so rapidly, that it was impossible to count them; but I should say, on a rough calculation, there were about twenty or twenty-five within a second. Some were small and burned dimly; others flashed with a bright flame, in a direction almost parallel with the ground, and coinciding with that of the wind, which was rather brisk. After having for some time looked with amazement at the brilliant scene, as a whole, I tried to study its details, and soon found that the flames which were nearest originated in a quagmire, the position of which I knew exactly, by a solitary cluster of willows; and I could trace a succession of flashes from that spot to a certain point of the margin of the wood across the rivulet and meadow. The distance of the two points from each other was more than half-a-mile, and the flames travelled over it, perhaps, in less than a second. The first flash was not always observed in the immediate neighbourhood of the quagmire; but the succession of flames lay always in the same straight line, and in the direction of the wind; whilst other sets were observed, though not with the same distinctness, in the more distant parts of the meadow-ground.
"After about an hour, a bank of mist began to overspread the meadows, but I saw the light still glimmering through it, whilst I dressed myself, in order to examine the phenomenon in its laboratory. However, when I reached the meadows, the atmospheric conditions which gave rise to the ignes fatui had ceased to exist." Weissenborn then expresses his belief that the phosphoric hydrogen gas, exhaled by certain swamps, is kindled into flame by coming in contact with the atmospheric air; but, as the hydrogen is not saturated with phosphorus, there is a certain electric condition of the atmosphere necessary to cause the combustion. Thus, under common circumstances, the gas is evolved and dissipated without being observed; but when the state of the atmosphere is competent to effect its combustion, the proper degree of electrical tension is lost at the place where the explosion is effected; and, until it is restored, or the gas comes in contact with that layer of the atmosphere which possesses the requisite degree of electrical tension, a considerable body of bog gas may collect, and be carried in the direction of the wind, so as to give rise to a sort of quick fire, with occasional flashes; in those places of the stream of gas where there happens to be a considerable volume of it. The lights, which still frequently excite apprehensions in Wales, and are popularly termed "corpse candles," have the same origin as the "ignes fatui."
At the village of Wigmore, in Herefordshire, there are fields which may be, and two houses which really are, illuminated with a natural gas. This vapour, with which the subjacent strata seem to be charged, is obtained in the following manner:--a hole is made in the cellar of the house, or other locality, with an iron rod; a hollow tube is then placed therein, fitted with a burner similar to those used for ordinary gas-lights, and immediately on applying a flame to the jet, a soft and brilliant light is obtained, which may be kept burning at pleasure. The gas is very pure, quite free from any offensive smell, and does not stain the ceilings, as is generally the case with the manufactured article. Besides lighting rooms, etc., it has been used for cooking; and, indeed, seems capable of the same applications as prepared carburetted hydrogen. There are several fields in which the phenomenon exists, and children are seen boring holes and setting the gas on fire for amusement. It is now several months since the discovery was made; and a great many of the curious have visited, and still continue to visit, the spot.
If the Chinese are not manufacturers, they are, nevertheless, gas consumers and employers on a large scale; and have evidently been so, ages before the knowledge of its application was acquired by Europeans. Beds of coal are frequently pierced by the borers of salt water; and the inflammable gas is forced up in jets twenty or thirty feet in height. From these fountains, the vapour has been conveyed to the salt-works in pipes, and there used for the boiling and evaporation of the salt; other tubes convey the gas intended for lighting the streets, and the larger apartments and kitchens. As there is still more gas than is required, the excess is conducted beyond the limits of the salt-works, and forms separate chimneys or columns of flame.
A singular counterpart to this employment of natural gas, is witnessed in the valley of the Kanawha, in Virginia. The origin, the means of supply, the application to all the processes of manufacturing salt, and of the appropriation of the surplus for the purposes of illumination, are remarkably alike at such distant points as China and the United States.
It has sometimes been stated of a departed person, that a luminous appearance was observed to rest upon, and occasionally to surround, a corpse. Such an effect has been described as supernatural--a Divine attestation to extraordinary excellence; and, doubtless, Roman Catholics have made the most of such circumstances in reference to those whom they have denominated saints, and to whom a place has been assigned in their calendar. And yet there was no departure in any such instance from the ordinary laws of nature. Sir H. Marsh, in an essay on "The Evolution of Light from the Human Subject," states, that electric sparks have been known to issue from the skin of some individuals when rubbed lightly and quickly with a linen cloth. Not only has this physician heard of such cases, but two had actually come under his observation.
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