Melting

“ So, the heat that has been applied to the melting ice has been utilized during the process of its liquefaction in rearranging the water molecules and putting them in a state of strain, so to speak, like the weight that is wound up to a certain height. There is a certain amount of potential energy that is stored in the molecules of water that will be given up and become active energy in the form of heat, if the water is again frozen. ”

“ The result is that a snow coating is in effect an admirable blanket. When the sun shines upon it, much of the heat is reflected, and as the temperature does not penetrate it to any depth, only the superficial part is melted. This molten water takes up in the process of melting a great deal of heat, so that when it trickles down into the mass it readily refreezes. ”

“ Where can it get this
heat? We assume that we give it none. It has only two sources,
the ice can take heat from itself, and it can take heat from the
water. It does both in this case, and both ice and water drop in
temperature. They fall in temperature till -7.5° is reached. Then
the ice has got to its melting point under the pressure of one
thousand atmospheres, or, as we may put it, the water has reached
its freezing point. There can be no more melting. ”

“ Fig. 424.—Effects of differential melting and subsequent refreezing upon the glacier surface. a, dust wells; b, glacier tub produced by melting about a group of scattered dust particles; c, glacier star produced when the inclosed water of the glacier well has frozen in successive nights; d, “bath tub.”
If the dirt upon the glacier surface, instead of being scattered, is so disposed as to make a patch completely covering the ice to the thickness of an inch or more, the effect is altogether different. ”

“ Waste from melting also goes on to some extent on the bottom from heat stored up in the rocks, and given off slowly to the snow in contact with them, as is shown by the rising of the streams on all the higher regions after the first snowfall, and their steady sustained flow all winter. ”

“ Solids differ from one another in the temperatures at which they become liquid. These temperatures are called their melting points. Thus the melting point of ice is 32°; that of lead 612°; that of gold 5237°. [3] The heat which is supplied to a body during the processes of fusion or vaporization, and which does not affect the thermometer, or increase the temperature of the body fused or vaporized, is said to become latent. It can be proved to exist in the body fused or vaporized, and may even be taken from that body. ”

“ This process is the exact opposite of the formation of ice by evaporation; it is the atmosphere which is made humid by the vaporizing of the ice, and by the drip. When the air is thoroughly saturated with the vapor, being scarcely renewed from outside and but a few degrees above freezing point, it undoubtedly retards evaporation, acts like a blanket and lessens the rate of melting of the ice. ”

“ A volume of snow and ice covering the ground chills the air by direct radiation, and by contact lowers its general temperature, thus delaying or arresting the process of melting by the summer's sun. It is a familiar fact that in snow-covered regions the direct rays of the sun may be intensely hot, melting pitch from timber, or heating rocks, while the temperature of the air is that of the ice upon the ground. ”

“ If, on the other hand, the temperature over and about the ice field be lowered, melting will be diminished, and if the rate of movement be constant, the edge of the ice will advance farther than under the earlier conditions of temperature, since it has more time to advance before it is melted. ”

“ But imagine heat so great that masses of iron and copper are not only melted but turned into vapor. Then you have some idea of the intense heat that prevails on the stars. The rains that fall on earth are made up of drops of water, but the rainfalls on the stars must be drops of melting iron, while the clouds that form are sheets of molten metal. ”

“ However, we find that when a body is melting, vaporizing, or otherwise suffering an abrupt change in physical properties, a quantity of heat is absorbed which disappears without changing the temperature of the body. ”

“ The process of melting ice is very slow, because every portion must absorb or render latent a certain quantity of heat before it can take the liquid state—hence the difficulty of melting blocks of ice when they are surrounded with non-conducting materials ”

“ Although in general these suffer no changes but those due to the partial melting which takes place in summer, and the renewed accumulation which takes place in winter, yet when heavy rains fall upon the less elevated portions of the Alpine snow, they not only melt that snow much more rapidly than the summer sun would do, but they wash down large masses, which add largely to the destructive power of the descending waters. ”

“ The heat of the sun does not radiate from the sea with the same intensity as it does from the earth, whence the ice, drifting from the south into the oceans nearer the equator, melts more slowly, and is consequently enabled to travel longer distances, thus lowering the temperature of the surrounding atmosphere and still further delaying the melting process. ”

“ The transition of water to ice, and of ice to water, produces important changes in the temperature of surrounding objects. We are often made painfully sensible of the chilling influence of the atmosphere when its heat is rapidly abstracted in the melting of large masses of ice and snow. But the reverse of this takes place in freezing. The crystallization of water is attended with an elevation of temperature. The heat which vapor carries with it in its aërial journeys is liberated when those vapors are transformed into flakes of snow. ”

“ When for a period of years the rate of melting of the ice is diminished, or the snowfall increased, or both, the ice edge advances to a new line where melting is more rapid than at its former edge. The edge of the ice would tend to reach a position where waste and advance balance. ”

“ The ice once formed in such cavities, only melts slowly; for one knows that ice in melting, absorbs 60° of heat; and where find this heat in an air always very cold and nearly still? During a great cold, the ice forms with great promptness, while it melts with much slowness, even when the temperature of the air is several degrees above zero; what must then not be this slowness when the temperature of the interior air only rises in summer one degree above freezing point. It would need several summers to melt this ice if it did not reform each winter. ”

“ During that time the heat must accumulate to almost the melting point of lead; while, on the other hand, the absence of the sun for an equal period must be followed by a period of intense cold, such as we have no experience of, even in the Arctic regions. ”

“ In certain fields of permanent snow, particularly near their boundaries, some very lowly forms of vegetable life may develop on a frozen surface, drawing their sustenance from the air, and supplied with water by the melting which takes place during the summertime. ”

“ Some have even assumed the melting point to be less than thirty miles, when “the next contiguous matter is in a state of fusion, at a temperature probably higher than any that man can produce by artificial means, or any natural heat that can exist on the surface.” ”

“ That by melting without any addition, it seems to purge itself partly into the vitrescible matters it includes, since it emits to its surface small drops of glass, which form pretty considerable masses, and which we can easily separate after refrigeration. ”

“ See a good summary of this idea in Black's Lectures on Chemistry, vol. i. p. 118. Contrasting his theory of heat with that previously received, he says, ‘But, were the ice and snow to melt as suddenly as they must necessarily do, were the former opinion of the action of heat in melting them well founded, the torrents and inundations would be incomparably more irresistible and dreadful. They would tear up and sweep away every thing, and that so suddenly, that mankind should have great difficulty to escape from their ravages.’ ”

“ The change of snow into ice is owing to alterations of temperature, to partial melting and subsequent freezing, constantly renewed,—and also to the sinking of the mass upon itself in consequence of its own weight, the lower portions being thus forced out by the pressure of the superincumbent ice. ”

“ In their melting, also, the surface air is chilled, and winds from the north convey this chilled air far to the south, thus spreading widely over the warmer zones the frost-inducing influence of the melting snows. ”

“ For each additional atmosphere of pressure—a weight amounting to about fifteen pounds to the square inch—the temperature at which the ice will melt is lowered to the amount of sixteen thousandths of a degree centigrade. If we take a piece of ice at the temperature of freezing and put upon it a sufficient weight, we inevitably bring about a small amount of melting. Where we can examine the mass under favourable conditions, we can see the fluid gather along the lines of the crystals or other bits of which the ice is composed. ”

“ Whenever, by the melting of the lower portion of any part of a glacier, a piece of it cracks and falls to a lower level, the friction of the broken sides will produce heat, and melt a small portion of water. This water, trickling down very slowly, will form a thin layer on the broken surface, and a portion will be retained in the narrowest part of the crack. But, since the temperature of a glacier is very near the freezing point, that water will freeze very slowly. ”

“ And whereas after melting, it grows hard by the Cold, viz. is coagulated, and grows stiff, that comes from the other five metals, ♃, ♄, ♂, ♀, and ☽; in these five metals the Cold dwells and bears sway, and therefore ☉ cannot be fluid out of the fire, because of Cold. ”

“ This mass of snow and ice does not remain stationary, as might be expected from its apparent solidity. Under the influence of its own weight and of alternations of heat and cold, it flows down the incline like a very thick liquid. During the winter the ice melts but little, and the movement is slow, but in the summer, under the influence of the warm days and cool nights, both the melting and the rate of flow of the ice are increased. ”

“ The fire which is hot enough to melt a lump of ice may not be hot enough to melt an iron poker; on the other hand, it may be sufficiently hot to melt a tin spoon. Different substances melt, or liquefy, at different temperatures; for example, ice melts at 0° C., and tin at 233° C., while iron requires the relatively high temperature of 1200° C. Most substances have a definite melting or freezing point which never changes so long as the surrounding conditions remain the same. ”

“ The slowness of the thawing will surprise most people who have not previously tried the experiment. It takes about as long to melt this snow as it would to raise an equal weight of water from 32° to 174°. Or, if a pound of water at 174° be mixed with a pound of snow at 32°, the result will be two pounds of water at 32°; 142° will have disappeared without making the snow any warmer, it will all have been used up in doing the work of melting. ”

“ Equivalence of Heat and Work; heat produced by Mechanical Action; heat consumed in producing work; Chemical Attractions; Attraction of Gravitation; amount of heat which would be produced by the stoppage of the Earth in its Orbit; amount produced by the falling of the Earth into the Sun; shifting of Atoms; heat consumed in Molecular Work; Specific Heat; Latent Heat; 'friability' of ice near its melting point; Rotten Ice and softened Wax
20. 334
Papers presented to the Royal Society by Professor Forbes in 1846; Capillary Hypothesis of glacier motion; hypothesis examined
21.—Thomson's Theory. ”

“ At night the earth gets cold. The water-gas, if the night is calm, comes out of the film of air next to the earth. It settles in the form of tiny drops on everything around.
“When the earth gets very cold, the water freezes as it changes from gas to water, and instead of dew we have frost.”
“Oh, that is why we have frost on the inside of the window panes in winter,” said Frank.
“That is so,” said his uncle. “The frost on your window pane is the water-gas of the warm room changed into particles of ice. But let us come back to our steam puff. ”

“ Other things, such as stones, are melted only by terrific heat.
When the little particles of water that make up the clouds become very cold, they freeze as they gather and so make snowflakes. When the little particles of water in the air, that usually make dew, freeze while they are gathering on a blade of grass, we call it frost. When [pg 98] raindrops are carried up into colder, higher air while they are forming, they freeze and turn to hail. When snow or frost or hail or ice is heated, it melts and turns back to water. ”

“ In order to melt one cubic foot of ice, as much heat is required as would heat a cubic foot of water from the freezing point to 176° F., or two cubic feet to 88° F. To melt a layer of ice a foot thick will therefore use up as much heat as would raise a layer of ice-cold water two feet thick to the temperature of 88° F.; and the effect becomes still more easily understood if we estimate it as applied to air, for to melt a layer of ice only 11⁄2 inches thick would require as much heat as would raise a stratum of air 800 feet thick from the freezing point to the tropical heat of 88° F.! ”

“ Ice forms, and every particle of water is swollen by the change. A strain is put upon the mineral particles against which the particles of ice crowd for more room. Frost is a very powerful agent in the crumbling of rocks, as well as of stubborn clods of earth. In warm climates, and in desert regions where there is little moisture in the rocks, this destructive action of freezing water is not known. In cold countries, and in high altitudes, where the air is heavy with moisture, its greatest work is done. ”