Freezing point

“ We often witness the fact that water will not freeze if in rapid motion, although it be much colder than the freezing-point; but in this case will freeze at the bottom where its motion is retarded, forming what is called "ground, or anchor ice." The sandy bottom beneath swiftly-flowing streams is sometimes frozen solid by radiation of its heat to the cold water flowing over it. But no ice will form at the bottom of a pond or lake if the water be at rest; it then forms upon the surface only. ”

“ 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. ”

“ Powder snow acquires a crust if it is exposed to wind, to sun shining at a sufficiently direct angle, and to an air temperature above freezing. Wind alone has the power of forming crust without a preliminary melting of the surface. I do not know why this should be so, but no doubt the reason is to be found in the law that pressure lowers the freezing-point, so that the increased pressure caused by wind lowers the freezing-point, or, in other words, produces the effects of a thaw at the point where the [Pg 409] wind acts even though the general air temperature may be well below zero centigrade. ”

“ There is nothing in the study of the atmosphere that so intimately concerns the horticulturist and the gardener as knowledge of the conditions under which frost forms, and the methods that may be pursued to gain immunity from its disastrous effects, or to lessen the loss.
Frost does not necessarily form from air that has fallen to the freezing point, as many suppose. On the contrary, the air ten feet or less above the vegetation may be several degrees above freezing when there is a heavy and destructive frost upon vegetation. ”

“ There can be no question of the severity and length of the winters, but then we were told on all sides, with a concurrent testimony that could not be disputed or doubted, that the exceeding dryness of the climate renders the most excessive cold of very much less actual consequence to the sufferer than it would be in a country where there is moisture in the air. In fact in these Prairie regions, when the thermometer is perhaps 15° or 20° below freezing point, the cold is not so severely felt as with us when it is only 2° or 3° below 32°. ”

“ Nor does the air lose its moisture when below the freezing point. In all parts of the atmosphere, as at the surface of the earth in winter, moisture is held in large quantities in the coldest and severest weather; and it is not till it moderates, and a perceptible electric change takes place, that it is precipitated as rain or snow. Doubtless there is an exposure of considerable surfaces, of opposite currents, charged with opposite polarity, and a constant depolarization where [Pg 88] their surfaces meet. ”

“ The fact that the temperature in winter has been proved by actual experimentation to fall as low as 28° Fahrenheit, that is, four degrees below the freezing-point at a depth of six feet below a thick covering of snow, though not absolutely conclusive as to the temperature at a greater depth, is certainly very significant. ”

“ The number of degrees lying between the critical point and the normal freezing-point is complicatedly dependent on the rapidity of cooling, but the alternatives are so various that it is impossible at present to draw any concise conclusion with regard to them. It is an extremely interesting discovery that males have normally a greater difference between their critical and normal freezing-points than females ”

“ The difference consists only in this, that a change from -40° upward to about zero is usually a very welcome one, while from zero to the freezing point, as in the instance just alluded to, it becomes, to persons in our situation, rather an inconvenience than otherwise. This may be more readily imagined by considering that our clothing, bedding, fires, and other precautions against the severity of the climate having been once adapted to a low degree of cold, an increase of temperature renders them oppressive and inconvenient ”

“ Could two such currents of water meet anywhere at sea, except as upper and under currents? If water that freezes at 32°, that grows light and remains on the surface as you cool it below 39°, is prevented from freezing in our great fresh-water lakes by vertical circulation, how much more would both vertical and horizontal circulation prevent congelation in the open polar sea, that is many times deeper and larger than the lakes, and the water of which contracts all the way down to its freezing-point of 27°.2'! ”

“ At a temperature considerably below freezing point snow commonly falls in the condition of fine grains that do not cohere when they meet, and, in a mechanical sense, differ from those of sand only by being lighter. Our observations on the relation between the form of the larger ridges and the smaller ripple marks, and the direction of the wind, quite agree with those published by Maw. ”

“ If cold it cools the air and the earth somewhat while passing through or over them, but produces no permanent effect on temperature, because a few hours of sunshine restore to the air or the surface-soil all the heat they had lost. But if snow falls for a long time, the effect, as we all know, is very different, because it has no mobility. It remains where it fell and becomes compacted into a mass, and it then keeps the earth below it and the air above, at or near the freezing-point till it is all melted. ”

“ For several thousand feet down, as far as the 10,000-foot level, in fact, does the snow retain this granular consistency. One reason for the slowness with which it compacts is found in the low temperatures that prevail at high altitudes and preclude any considerable melting. The air itself seldom rises above the freezing point, even in the middle of the day, and as a consequence the snow never becomes soft and mushy, as it does at lower levels. ”

“ 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. ”

“ The condensed vapour or cloud particles are here supposed to be carried up with the cooling air, but the temperature of freezing or zero degrees centigrade is soon attained—as the diagram shows—when the pressure is about 472 millimetres. At this point the special evolution of latent heat of freezing comes into play; and although the air rises higher and more moisture is condensed, the temperature does not fall because the water already converted into vapour and now becoming ice is giving out latent heat sufficient to counteract the cooling due to expansion. ”

“ If you take a piece of this solid substance, you find it to be cold, brittle, and transparent. Brought into a warm room it soon melts into water, and you may drive off the water as before into vapor. Ice is the general name given to water when it is in the solid state, such forms as snow and hail being only different appearances which ice puts on. Whenever water becomes colder than a certain temperature it passes into ice, or freezes, and this temperature is consequently known as the freezing-point. ”

“ This man did not know cold. Possibly all the generations of his ancestry had been ignorant of cold, of real cold, of cold one hundred and seven degrees below freezing point. But the dog knew; all its ancestry knew, and it had inherited the knowledge. ”

“ Alone, what did Bloom feel?
The cold of interstellar space, thousands of degrees below freezing point or the absolute zero of Fahrenheit, Centigrade or Réaumur: the incipient intimations of proximate dawn. ”

“ 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. ”

“ When the clouds are overcharged with moisture in cold climates or in cold weather, the vapour freezes as it condenses and forms snow, which under the microscope presents a series of the most beautiful star-like crystals (fig. 3) ; the same result is produced by the freezing of the vapour or fog near to the earth's surface, this is called "hoar-frost," which is (like dew) deposited on those parts of the surface most cooled by radiation. Hail is caused in all probability by the drops of rain passing through a cold stratum of air and becoming frozen as they fall. ”

“ For the layer of ice formed, being lighter than water, floats on the surface of the latter, and thus forms a protective layer and prevents to a large extent further freezing, except as a slow thickening of the layer, the total freezing of the water of a lake or river being rendered practically impossible, an obvious provision for the security of life of the piscatorial and other inhabitants of the waters. ”

“ It is the air entangled among the snow crystals, then, which makes the snow blanket, as we often call it, so sure a protection from cold. The ground may have frozen to a considerable depth before the snow comes, but if it stays throughout the winter there is no frost in the earth beneath it when the spring melts it away. No sooner is the ground protected from further freezing from above than the greater warmth below begins to melt the frost and change it to life-giving moisture. ”