In Iceland and Germany the thermometer frequently falls to zero, which is 32 degrees below the freezing point. At Hudson’s Bay it has been known to sink even 50 degrees lower. When stones or metals, which have been exposed to such degrees of cold, are touched by the tongue, or the softer parts of the human body, they absorb the heat from those parts with such rapidity, that the flesh becomes instantly frozen and mortified, and the principle of life in them is extinguished. Some French academicians, who made a journey to the northern end of the Baltic, and wintered under the polar circle, found it necessary to use all possible precautions to secure themselves from the dreadful cold which prevailed. They prevented, as much as possible, the entrance of the external air into their apartments; and if at any time they had occasion to open a window or a door, the humidity of their breath, confined in the air of the house, was condensed and frozen into a shower of snow; their lungs, when they ventured to breathe the cold air, felt as if they were torn asunder; and they often heard the rending of the timber around them by the expansive power of the frost on the fluid in its pores. In this terrible cold the thermometer fell to 33 below zero.[79] The most intense cold ever known in the neighborhood of London was on December 25th, 1796, when the thermometer indicated 2 below zero.
The ice at each pole of the earth forms an immense cupola, the arch of which extends some thousand miles over the continents; the thickness of which, beyond the 60th degree of latitude, is several hundred feet. Navigators have assigned to detached masses, which are met with floating at sea, an elevation of from 1,500 to 1,800 feet.[80] There can be no doubt but that the thickness of these cupolas of ice is much greater nearer the poles; for astronomy sometimes presents in the heavens so vast an image of them, that the rotundity of the earth seems to be considerably affected thereby. Captain Cook could never approach nearer the south pole, where there is no land, than the 70th degree of latitude; that is, no nearer than 1,500 miles; and it was only under the favor of a bay, that he was permitted to advance even so far.[81] All the results of observations made by navigators, concur in proving that the temperature of the sea decreases according to the depth; and that the deepest gulfs are continually covered with ice, even under the equator. From a late memoir by M. Perron, some say, there is reason to believe that these mountains of ice at the poles, which have hitherto impeded the progress of European navigators, have been detached from the depths of the sea to float at the surface.[82]
When water is converted into ice, it is lighter[83] than when in a fluid state, which is a circumstance of great importance. Galileo was the first who observed this. Ice consequently floats upon water, its specific gravity being to that of water as eight to nine. This rarefaction seems to be owing to the air-bubbles produced in water by freezing; and which, being considerably larger in proportion to the water frozen, render the body so much specifically lighter: these air-bubbles, during their production, acquire a great expansive power, so as to burst the containing vessels though ever so strong.
[The specific weight of ice is known to be less than that of water. Our author assigns a reason not entirely satisfactory. We must admit that the freezing of the upper stratum of water, although it may include the air which was in the water frozen, yet, it does not expel the air from the subjacent volumes of water. Hence the air in the water below will balance the effects of the air included in the ice.
It is a singular fact, and is regarded as a deviation from the general rule, that water expands in volume in proportion as its temperature is reduced below 40° Fahrenheit. It also expands by raising its temperature above this degree.
The expansion of the volume then, and not the enclosed air bubbles, is the cause of water being specifically lighter when converted into ice. But it remains to account for its expansion by a reduction of temperature.
This is a difficult question. It seems most probable that this expansion is owing to a peculiar arrangement, of the particles of water, in the act of crystallization, i.e. freezing. M. Mairan found that the particles of water, in the act of freezing, arranged themselves constantly at an angle of 60°, and by this arrangement increased the bulk of the water thus crystallized.
It is obviously a mistake to attribute the “expansive power” of freezing to the force of the inclosed air-bubbles: because the reduction of temperature would reduce this supposed expansion of the inclosed air. The true cause of the expansion of ice is supposed above, in the arrangements of the particles of water in the process of crystallization.
The power which disposes these particles to arrange, increases with the reduction of temperature, until the disposing power becomes sufficiently great to force every impediment to the inclination to arrange. Hence the strongest vessels burst in the process of freezing.
The impediments may restrain the accomplishment of the arrangement of the particles for a time, but the disposing power will overcome them, if the reduction of temperature go on; and when they are overcome suddenly, the crystallization will take place instantly. Hence the sudden rending of vessels, trees, mountain rocks, &c., upon the sudden congelation of water.
Even when there is no cause to impede crystallization, it is well known that the preparation to crystallize, or freeze, may be observed in the liquid; the particles seeming to be preparing to arrange themselves; and then, at a given stage of the preparation, they take their places suddenly, and thus we have ice.
This consummation may be retarded, or hastened by artificial means. Water may be reduced to a lower temperature by being kept still, than when agitated. And if it be cooled down to the lowest possible temperature, without congealing, it may remain fluid at that temperature for a long time. But if the vessel be suddenly struck; or the surface of the water touched with a piece of ice; or a large piece of cold metal be brought in contact with the outside of the vessel; the water will instantly crystallize or freeze in beautiful crystals.
These facts establish the above theory. Because, 1. there is no increased reduction of temperature effected, by striking the vessel, touching the surface of the water with ice, or the outside of the vessel with cold metal. 2. There is every reason to conclude these things commence the motion in the water, which is at rest, balanced between an inclination to be at rest, and an inclination to move in arranging the particles; the motion communicated overcomes this balance in favor of the disposition to crystallize, and hence the water freezes instantly, with an expansion of volume.]
It is owing to the expansion of water in freezing, that rocks and trees are often split during intense frosts. According to the calculations of the Florentine academicians, a spherule of water, only one inch in diameter, expands in freezing with a force superior to the resistance of 13½ tons weight. Major Williams also attempted to prevent this expansion; but during the operation the iron plug which stopped the orifice of the bomb-shell containing the freezing water, and which was more than two pounds weight, was projected several hundred feet with great velocity; and in another experiment the shell burst. This property of water is taken advantage of in splitting slate. At Colly Western, the slate is dug from the quarries in large blocks: these are placed in an opposite direction to what they had in the quarry, and the rain is allowed to fall on them: it penetrates their fissures, and the sharp frost freezes the water, which, expanding with its usual force, splits the slate into thin layers.[84]
M. Mairan, in a dissertation on ice, attributes the increase of its bulk chiefly to a different arrangement of the parts of the water from which it is formed; the icy skin on the water being composed of filaments, which according to him, are found to be constantly and regularly joined at an angle of 60°; and which, by this angular disposition, occupy a greater volume than if they were parallel. He found the augmentation of the volume of water by freezing, in different trials, a 14th, an 18th, a 19th, and when the water was previously purged of air, only a 22d part: that ice, after its formation, continues to expand by cold; for, after water had been frozen to some thickness, the fluid part being let out by a hole in the bottom of the vessel, a continuance of the cold made the ice convex; and a piece of ice, which was at first only a 14th part specifically lighter than water, on being exposed some days to the frost, became a 12th part lighter. To this cause he attributes the bursting of ice on ponds.
Several philosophers have been very desirous to experience how far the expansive force of freezing water might be carried. “An iron gun of an inch thickness,” says M. Haüy, “filled with water and exactly closed, having been exposed by Buot to a strong frost, was found to be burst in two places at the end of twelve hours. The Florentine philosophers were able, by means of the same cause, to burst a sphere of very thick copper; and Musschenbroek, having calculated the effort which would occasion the rupture, found that it would be capable of raising a weight of 27,720 pounds.”
“Colonel E. Williams, of the Royal Artillery, when at Quebec, in the years 1794 and 1795,” says Dr. O. Gregory, “made many experiments. He filled all sizes of iron bomb-shells with water, then plugged the fusee-hole close up, and exposed them to the strong freezing air of the winter in that climate; sometimes driving in the iron plugs as hard as possible with a sledge-hammer: and yet, though they weighed near three pounds, they were always forced out by a sudden expansion of the water in the act of freezing, like a ball impelled by gunpowder, sometimes to the distance of between 400 and 500 feet: and when the plugs were screwed in, or furnished with hooks and barbs, by which to lay hold of the inside of the shell, so that they could not possibly be forced out; in that case the shell was always split in two, though its thickness of metal was about an inch and three quarters. It is further remarkable, that through the circular crack, round about the shells where they burst, there stood out a thin film or sheet of ice, like a fin; and in the cases where the plugs were projected by freezing water, there suddenly issued from the fusee-hole a bolt of ice of the same diameter, and stood over it sometimes to the height of eight inches and a half. Hence we need not be surprised that excessive frost should cause the ice to split rocks, and other solid substances.”[85]
It was necessary for the preservation of the world, that water should in this instance be subjected to a law different from that of other substances which change from fluid to solid. The wisdom and goodness of the great Artificer of the world will manifest itself in this arrangement, if we consider what would have been the consequences had water been subject to the general law, and like other fluids, become specifically heavier by the loss of its caloric. In winter, when the atmosphere became reduced to 32°, the water on the surface of our rivers would have sunk as it froze; another sheet of water would have frozen immediately, and sunk also; the ultimate consequence of which would have been, that the beds of our rivers would have become repositories of immense masses of ice, which no subsequent summer could unbind; and the world would shortly have been converted into a frozen chaos. How admirable the wisdom, how skilful the contrivance, that by subjecting water to a law contrary to what is observed by other fluids, as it freezes it becomes specifically lighter, and, swimming upon the surface, performs an important service by preserving a vast body of caloric in the subjacent fluid from the effects of the surrounding cold, ready to receive its own accustomed quantity on the first change of the atmosphere?[86]
Owing to the distance of this globe from the sun, and to the vast mountains of ice at the poles, the atmosphere over a large portion of the earth is at times reduced to so low a temperature, that, if it were not for a wise provision of nature, all vegetable life must be destroyed. Caloric has always a tendency to equilibrium; therefore, if the temperature of the air be lowered, the earth cools in proportion: but when the atmosphere is reduced to 32°, the water which it held in solution becomes frozen, and precipitates in the form of snow on the earth, covering it as with a carpet, and thereby preventing the escape of that caloric which is necessary for the preservation of those families of vegetables that depend on it for their support and maturity. Be the air ever so cold, the ground, thus covered, is seldom reduced below 32°, but is maintained equably at that temperature for the purpose above mentioned.[87] Homer has described a shower of snow, and its extensive effects, in a fine strain of poetry.