Ice, water or other fluid solidified by freezing. Various liquids become partially solid at low temperatures, but this is commonly owing to the water of which they are in part composed; and none of them produce a clear uniform solid like that of frozen water. At 32° F. under ordinary circumstances water begins to crystallize. Slender prisms, usually of six sides, and terminated by six-sided pyramids, form in it, and arrange themselves in lines crossing each other at angles of 60° and 120°. The presence of salts in solution impedes this process, and when at last it takes place at a temperature below 32°, the greater portion of the foreign matter is excluded from the ice, which consequently is nearer the composition of pure water. Advantage is taken of this in some operations designed to concentrate the strength of liquors, as of vinegar, the portion that first crystallizes by cold being removed, and leaving the residue less diluted. Pure water contained in a polished vessel and kept perfectly quiet may be reduced to several degrees below the freezing point without freezing; but agitation or the introduction of foreign bodies will cause congelation to take place suddenly, and as the ice is formed latent heat is liberated, and the temperature rises to 32°. Saline solutions sometimes exhibit a similar reluctance to deposit their salts in crystalline form even when reduced by evaporation below their point of saturation; and in these cases crystallization is often suddenly induced by the same methods that cause the water to congeal.

From about 39° water expands as its temperature is reduced, with the exertion of prodigious force. A hollow globe of brass with a cavity only an inch in diameter, filled with water, has been burst by the freezing of this, exerting a force, as estimated, of 27,720 lbs. The effect of this property is seen in the tendency of ice to plough up the banks of ponds, to split off masses of rock from mountain cliffs, and to 'loosen and pulverize the soil through which it is diffused. The effect last named is not perceived till the thaws of spring, when the frost is said to come out of the ground. This force has been artificially applied to splitting rocks and trunks of trees by allowing water to freeze in their fissures. This expansion, estimated by Boyle at one ninth the original volume, gives to ice less density than that of water, so that it floats. Its specific gravity by this estimate should be 0.9; M. Brunner in his series of experiments found it to vary from 0.918 at 0° C. to 0.92025 at - 20° C. But for this exception, which is however not a singular one, to the usual law of increase of density by reduction of temperature, ice as it forms would sink to the bottom, and there accumulate beyond the reach of atmospheric heat; great collections of water would be chilled throughout, and their fitness for sustaining life in cold regions be entirely destroyed.

But as the ice, a bad conductor of heat, covers the water, it serves as a protecting sheet to retain the warmth below, and preserve the water from the extreme temperature that prevails above. As the cold increases, the solid ice is found to be subject to the usual law, contracting as found by Brunner more than other solids; and upon ponds in excessively cold weather it contracts, and in shrinking parts asunder in the weakest places with loud reports. A form of ice called anchor ice is often seen in cold weather attached to objects at the bottom of streams. Its character is explained by Prof. Dewey on the supposition that the whole body of water is cooled below the freezing point, but under conditions of quietness opposed to the formation of ice. The substances at the bottom serve as points of congelation, like those introduced into saline solutions to cause crystallization to take place, and ice forms upon them. It is observed to gather in a clear cold night, when the surface of the water is not frozen, and its temperature is at the freezing point, that of the air being still lower. The layers of ice are sometimes 3 in. thick; and as soon as they are detached from the bodies which hold them down they rise to the surface.

In some of the crevasses of the Alpine glaciers immense icicles from 20 to 30 ft. long were found by Tyndall, hanging from the coping of snow which lines the edges of the chasms. Near the poles, and on mountains at a certain height in all latitudes, there are immense masses of what may be considered permanent ice; and there are said to be places in Siberia, even where there is a limited culture of the ground, where ice is always found at a certain depth below the surface. In a well which was sunk at Yakutsk the earth was found firmly frozen to the depth of 382 ft., some of the strata being entirely of ice. From the exposed polar ice fields and glaciers great masses become detached and form icebergs. (See Icebergs.) - The regelation of ice, a phenomenon first distinctly observed by Faraday, has recently attracted much attention, especially in regard to a controversy on the subject of glaciers. Regelation takes place between blocks of ice where they are strongly pressed together, even in warm water, and in cold water it will take place when the masses only touch each other. When fragments of ice are subjected to pressure in a mould, they may be formed into a solid block. When but little pressure is used, it is necessary that the ice should be but little below the freezing point.

This is the explanation of snow-ball making. As the freezing point of water is lowered by pressure, it is easy to understand how this formation of solid blocks from fragments may take place. A certain degree of viscosity, approaching liquefaction, is produced, by which the particles are reunited, and are firmly held as soon as the pressure is removed or lessened. The motions of glaciers, attended as they are by alterations in the form of immense masses of ice, is explained by this property that ice has of liquefying under enormous pressure. Mountains of ice squeezed into crevasses must exert a force which we probably cannot produce by any artificial means, and as a consequence the ice may be made viscous when at a temperature considerably below the freezing point. For other properties of ice, see Glacier, Snow, and Freezing, Artificial. - Ice Trade. Ice was little known as an article of commerce until the early part of the present century. In the 17th century its use was so common in France that many dealt in it and in snow, gathering these in winter and packing them closely in pits surrounded with straw or other non-conducting substances and protected from the air.

The Italian peasants also have long found a profitable business in collecting the snow upon the Apennines and storing it in the caves of these mountains to supply the large demand at Naples. The bodies of ice found in the recesses of Mount Etna, and excavated sometimes from beneath beds of lava which have flowed over them, are noticed in the article Etna. In the last century the gathering and storing of ice for summer use is known to have been practised in some of the middle states of the American Union, the receptacles for preserving it being deep cellars, placed so as to be readily drained, or from which the water was pumped out as it collected; but though most wanted in countries where it is not naturally produced, no attempts had been made to transport it by sea. This was first done by Mr. Frederick Tudor of Boston, who sailed with a cargo of 130 tons in his own brig to Martinique in 1805. He persevered in the business, though making little or no profit, till after the close of the war of 1812. In 1815 he obtained the monopoly of the Havana business and important privileges from the Cuban government.

In 1817 he introduced the trade into Charleston, S. C, the next year into Savannah, and in 1820 into New Orleans. Frequent disasters attended his enterprises, and in 1832 his entire shipments amounted to only 4,352 tons, the whole of which came from Fresh pond in Cambridge. In May, 1833, he sent the first cargo of ice to the East Indies, which was delivered at Calcutta in the autumn of that year. Of 180 tons, one third was wasted on the voyage, and 20 tons more in going up the Ganges. It was packed in large blocks closely fitted together between a double plank casing filled in with dry tan. The ice was sold immediately at half the cost of that prepared by the natives. At the present time a waste of about one half is generally expected on this voyage. In 1834 the first cargo was shipped by Mr. Tudor to Brazil. Until 1836 he conducted the whole trade; but as it became profitable others began to enter into it, and from other ports besides Boston. That port, however, still has the great bulk of the trade, the shipments having been as follows, according to the incomplete returns that have been preserved:

In

1805........

180

tons.

,,

1816........

1.200

,,

,,

1826........

4,000

,,

,,

1836........

12,000

,,

,,

1846........

65,000

,,

,,

1856........

146,000

,,

In

1866........

124,751

tons.

,,

1868........

105,818

,,

,,

1870........

78,803

,,

,,

1871........

109,298

,,

,,

1872........

98,859

,,

,,

1873........

81,266

,,

Of the amount shipped in 1873, 30,333 tons went to coastwise and 50,933 tons to foreign ports. The total exports from the United States to foreign ports for the year ending June 30, 1873, were 53,553 tons, valued at $188,095, of which 48,890 tons, valued at $175,848, were from Boston; 14,449 tons were shipped to Cuba, 13,342 to the East Indies, 10,186 to the British West Indies and British Honduras, 4,392 to British Guiana, and the rest to other portions of the West Indies, South America, etc. Into the interior ice has been carried by railroad in considerable quantity as far as Knox-ville, Tenn. Some ice was formerly shipped to England, but the British market is now entirely supplied from Norway, the Norwegian ice being cheaper than the American, though of inferior quality. The imports into the United Kingdom in 1872 amounted to 139,421 tons, valued at £128,251. The chief difficulty in establishing the ice business in warm countries has been the necessity of constructing houses especially adapted for preserving the ice; and these to be profitable must be upon a large scale. One of these erected in 1845 at Calcutta, by Mr. Wyeth of Cambridge, covered more than three fourths of an acre, and was capable of holding 30,000 tons of ice.

Its walls of brick were triple, with flues or air spaces between; their length was 198 by 178 ft., and their height 40 ft. The building was covered by five roofs, and between every two contiguous ones were air spaces. - New York city is supplied with ice chiefly from small lakes near the Hudson river, or from the river itself above New burgh. The whole amount gathered when the season is favorable is about 1,160,000 tons, of which 200,000 tons are from the lakes (Rockland lake in Orange co. supplying 80,000 tons), and the rest from the river. Deducting one third for wastage, we have 774,000 tons, the amount required to supply the present demand of New York and Brooklyn. The demand increases at the rate of about 70,000 tons a year. With the growth of the business upon the coast it has also spread in the interior, where, especially near the large towns, the gathering of ice is now an important business. The great lakes furnish supplies which are carried by railroad to the cities lying south, and through the Illinois river ice is sent down the Mississippi. In the autumn the ice boats come up to the vicinity of Peru, 111., where they are allowed to be frozen in. In the winter they are filled, and in the spring when the ice breaks up they float down with their freight.

The ice produced in deep ponds by the severe cold weather of New England is particularly adapted by its hardness and compactness to keep well, while the purity of the water gives it clearness and renders it especially agreeable. The ice obtained from the Kennebec river is most celebrated. That formed upon the shallow waters of Great Britain is found to be porous and very inferior in durability to that from the United States of the same thickness. - The methods of gathering and storing ice are entirely American. When the ice is 9 in. to a foot thick, or if for exportation 20 in. thick, the snow, if there be any, is cleared off the surface with wooden scrapers, each drawn by one horse. Another scraper armed with a steel blade planes off the porous upper layer to the depth of 3 in. or more if necessary. The surface is then marked off in large squares by a sort of plough drawn by a horse, which cuts a groove about 3 in. deep. A machine somewhat like a harrow, with three or more parallel rows of teeth, which may be 22 in. apart, is next drawn along the lines already made, one row of teeth running in the grooves as a guide; and as many more cuts are made as there are more rows of teeth. This is repeated upon the cross lines, and the whole area is thus cut into small squares.

If necessary, a deeper plough is afterward run through all the grooves to increase their depth. A row of blocks is then sawn out by hand, and being taken out or thrust under the others, room is made for splitting off the adjoining squares, which is done by an ice spade dropped into the grooves. In very cold weather the ice yields readily to a slight wedging force. The blocks are sometimes floated through the canals opened in the ice to the shore, where they are hoisted out; and they are also sometimes jerked with a hook at the end of a pole up a slide upon a platform placed at the edge of the opening, and from this platform they are slid along on the sleds which convey them away. At the ice houses the blocks are raised often by steam power up an inclined plane to the top of the building, and thence let down another plane to any part within where it is required for packing. The storehouses, huge wooden buildings without windows standing around the edges of the ponds or along the banks of the rivers, present a very singular appearance. They are from 100 to 200 ft. long and very broad, with a capacity sometimes exceeding 20,000 tons. One at Athens on the Hudson holds 58,000 tons, and two at Rockland lake in Orange co., N. Y., hold 40,000 tons each.

Around Fresh pond at Cambridge, Mass., there is a large number of these buildings. Between their walls they are filled in with saw dust. As the season of the ice harvest is short and uncertain, the gathering of the crop is conducted with the greatest activity at favorable times.