HARVESTING AND MANUFACTURING

The general law of the formation of ice is that freezing takes place when the temperature of water is reduced to 320 Fahrenheit. Salt water does not freeze until it is cooled to 280. Water does not need to be still to freeze. On the contrary, when absolutely motionless, water can be reduced to a temperature of 150 before the formation of a particle of ice, a slight agitation then, however, causing crystals to appear at once. In a lake, pond or river the whole body of water cools down to 400, its point of maximum density, before freezing over. It has been discovered by the United States Signal Service officers that the water usually stands at that temperature for several days before the formation of ice. When the lake or river has cooled to 40⁰, and the atmospheric air stands at 32⁰ or less, ice forms on the top of the water during any few hours when the surface is not ruffled by a breeze. Crystals shoot out in every direction. The interstices are filled with other crystals, until a thin film of solid ice is formed, and then by the same process the film grows thicker and thicker with each succeeding clay during which the temperature of the body of air above remains below 32⁰ Fahrenheit. The colder the weather and the steadier the freezing, the denser and clearer the ice, especially if upon the surface of a rivel.. So that in the more northern latitudes and on the rivers, as in the states of Maine, Vermont, northern New York, Michigan, and Wisconsin, the ice is usually harder, clearer, and slower to melt drat that which is formed on the southern edge of the frozen region. The hardest ice in the world, and the slowest to melt, is that formed on the tops of high mountain peaks, where it is exposed to severe and protracted cold.

It was long supposed that ice was an exception to the general rule governing the expansion and contraction of bodies near the melting point. In the light of later science it has been disclosed that the phenomena which occur in ice are characteristic of all solid substances, although in ice there is in exaggerated exhibition of it. Considering frozen water as a solid substance, its performances are strictly the same as those of other solids. When the temperature of' any fusible substance is raised it expands in volume until it reaches a certain maximum point. As the temperature increases the volume contracts until a point of maximum density is reached, after which, with increased heat, the volume will expand again until the substance changes into vapor, at which point there is a further large expansion. Ice at 1000 below zero is intensely hard and compact. At 16⁰ ice is of the same volume and density as at 32⁰. From 16⁰ it expands with heat until 24⁰ is reached, when it contracts again. At 32⁰ it melts, but still contracts in volume, until the temperature rises to 40⁰, when it begins to expand, and then goes on expanding almost indefinitely. True ice of 16⁰ temperature, perfectly pure and free from all trace of air, will sink in water of more than 48⁰.

The fact that ice continually changes in volume with the temperature of the weather is illustrated to those who live in the neighborhood of ponds and lakes by the continual booming of the ice (luring changes of weather.. On a clear cold night the whole body of the ice contracts, and cracks are rent in it with such force that there is a report like the discharge of a cannon. Again, in the spring time, when the temperature is rising, the whole field of ice expands, and either shoves up on the shore with a force that cuts down trees or it lifts and breaks here and there again with a booming sound like a distant battle of artillery. Young people who are skating at night when the ice is booming are often mystified and alarmed at the phenomenon.

The waters preferred for ice-cutting are small deep lakes away from towns, where the water is pure, and rivers which are not contaminated by the drainage of towns and cities. Pond ice is apt to be full ci white streaks, composed of minute bubbles of air, and the presence of air is disadvantageous, as it renders the cakes porous• and liable to waste rapidly both iii the ice-house and in the wagons, cars, and ships in which it is distributed. A current through a pond makes the ice better and the pond a more desirable place to cut. As a rule, the-clearer and more transparent the cakes the denser and more lasting is the ice. There is no better product in the country than that which is taken from the rivers of Maine. The streams come down from forest lands and the ice usually forms on them at a temperature nearer to zero than to 320. Opaque ice usually indicates the presence of air, but this is not always the case. When snow falls on good clear ice only a few inches thick, and' there is doubt about the continuance of cold weather, the field is often sunk or overflowed by boring holes 3 or 4 feet apart, so as to admit the water to the surface of the whole field. By coming directly iu contact with the cold air the mingled ice and snow quickly freeze, producing often a total thickness of cake sufficient for immediate cutting. Ice thus made is often opaque, but is not considered as necessarily inferior on that account. It shows good lasting qualities. On account of the appearance of the ice of this character, however, it is never harvested, except in emergencies. A deep lake is preferred to a shallow one, and a deep gentle river to a lake because of there being less air in each case successively in the ice formed. There is always air in water, but in a deep lake the water cools to the freezing point more slowly than in a pond, giving the water more time to part with its air; and in a river the current carries along the minute air bubbles and to a great extent prevents them from being entangled and locked up in the crystals of the growing ice. These points were formerly not much regarded, but in the light of the experience of the last fifty years the companies now keep them in view in locating the scenes of their annual operations.

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