ICE (AS., OHG. is. Ger. Eis). Water in the solid state. it is crystallized in the hexagonal system. Ordinarily the crystalline structure of a block of ice is not apparent. owing to the close contact and perfectly regular arrangement of the crystals. But when a piece of ice is exposed to radiation from any luminous source, as the sun, a glowing fire, a gas or oil flame, disintegra tion gradually takes place, and by the use of a lens, numerous small crystals may he seen stud ding the interior of the block; as the heat con tinues, these crystals expand and finally assume the shape of six-rayed stars of exquisite beauty. (fee article SNONN. The freezing-point of pure water is marked (1 on the Centigrade and Ilt'-aumur scales, and 32 on the Fahrenheit scale. The influence of change: of pressure On the freezing-point i,, so slight that for all ordi nary atmospheric- pressures the freezing•point of pure water may be considered a constant imam tity. Great pressures, however, have the effect of lowering the freezing•point very considerably, and by raising the pressure to many thousand pounds per square inch ice has been caused to melt at 0° F. By cooling pure and clear water cautiously, it may be 'undercooled; i.e. it may, under ordinary pressure, be obtained in the liquid state at temperatures several degrees be low its normal freezing-point. But this is quite different from the effect of high pressures; the state of 'undercooled' water is just as unstable as the state of a 'supersaturated* solution, and a slight disturbance may cause the whole mass to freeze very rapidly, just as it may cause rapid crystallization to take place in a supersaturated solution. The lowering of the freezing-point by pressure has furnished one of the theories ex plaining the motion of glaciers. This 'regelation theory' is illustrated by the following phe nomenon: If a holding heavy weights at its ends is thrown over a block of ice, it gradu ally cuts its tray through the block, and yet the latter remains- entire. Along the line where the wire presses upon the block, the melting-point is lowered, and fence the ice meltS and allows the wire to descend through a. minute distance; the water immediately above the wire then freezes, because it is freed from pressure, and at the same time the ice immediately below the wire melts, allowing the wire to descend a little farther. Thus melting and ahnost immediate regelation proceed until the wire has cut through the block. The freezing-point, of water. as that of any other liquid, is considerably lowered by dissolving in it substances of any kind, and sea water, on account of its salt, is found to freeze at —2.5° to —3.0° C. The solid separating out, under ordinary circumstances, from freezing sea water, is not a mixture of ice and salt, hut pure iee, and this fact has been utilized in two ways: (1) for concentrating brine in the manufacture of salt ; (2) for obtaining SWOCt drinking-water from the salt water of the sea.
Unlike most other substances, water, on pass ing front the liquid to the soli() state, does not eontract. but expands. Therefore ice, having a lower speeitie gravity than water, floats on its surface. The specific gravity of ire at its normal melting-point is 0.9IS. The specific heat of ice, i.e. the amount of heat required to raise its temperature 1° C.. is much less than that of water in the liquid state; within 30° C. below the freezing-point it is very near one-half, and at lower temperatures it is even somewhat less than one-half, that of water. In the process of melt
ing. ice absorbs more heat than any other solid (see FREE7ING•.MIXTURES), more than SO calories being required to melt one gram of ice: the same amount of heat would raise the temperature of the grain of melted water to S0° C. (176° F.).
Ice•PAcK. or Pm-K-ICE. A name given to the large sheets or pans of ice (flocs) which have united to form a pack, and which occupy the open surface of the gen. The ice is almost wholly the result of direct freezing of the superficial stratum of the ocean, continued through a suc cession of years to a possible thickness of 16 to 20 feet, and of snow accumulations on this sur face. Through 'shearing' and over-riding the ice-pack is frequently of greater thickness than would be brought about by freezing alone, and it is not rare to meet with *hummocks' on the borders of the pack 30 to 40 feet in height, anal more. The individual pans, sheets, or floes that help to build up the pack are of varying dimen shms, ranging from small cakes to solid sheets many mile: across, and a pack itself may meas ure a hundred miles, or even considerably more. Even where virtually unbroken, they may con tain here and there pockets or 'lakes' of inelosed water, and penetrating waterways (leads), con fleeting these lakes or wholly independent of them, are of common occurrence. The central part of the Arctic Itasin is frequently assumed, but perhaps without sufficient reason, to be occupied by a stationary pack; along its south ern border it. is freely moving, sending down those vast sheets of Ice which constitute the 'pack-drift.' The remarkable drift of the Prom has demonstrated that the northern pack was still moving close to the Sfith parallel of north latitude, or within less than 300 miles of the l'ole. The strong southerly drift of the pack ice in the region about Greenland, Grinnell, and Grant Lands, jamming between the opposing land-masses, is that which has so largely baffled exploration along what is known as the 'Ameri can route' to the Pole. The great centrally lo cated ice-mass which in Davis strait. and Ilatlin's Ray separates Greenland on the east, from the disconnected lands of Arctic and sub-Aretie America on the \Vest, is known by whalers and others as the 'Middle Pack.' The Antarctic pack is less thoroughly known than the Arctic, although its extent appears to be very noel greater, and during many years its front edge or that, of the pack-drift has passed far beyond (northward of) the Antarctic Circle. Various names have been given by navi gators to particular conditions of ice. The bor der of sea-ice which clings to the land, and is not affected by the movements of tides, is called the ice-foot. lee that has been crushed into frag ments by the impact of moving floes is called rubble. A piece of ice that floats with the upper surface just awash is called a growler. Anchor ice or ground-ire is fresh-water ice that has frozen to the bottom of a lake or river. Young ice is ice new-formed, in distinction from ice of previous seasons. Pahroerystie ice is ice that has been formed during a number of seasons by floes overlaid one upon another, has been in creased year by year by snowfall, and has been welded by sun and rain into a single mass. See ARCTIC REGION: ANTARCTIC 'REGION.