ICARUS. See DIEDALLS, ante.
ICE is water in the solid form. It is specifically lighter than water which is just about to freeze, and therefore swims in it. Water, in becoming solid, expands about one ninth of its volume or bulk. The formation of ice takes place generally at the surface of water. This is owing to the peculiarity, that when water has cooled down to within 7°.4 of freezing, it ceases to contract, as before, with increase of cold, and begins to expand until it freezes; which causes the coldest portions of the water to be always floating on the surface. In some circumstances, however, not very well explained, ice forms at the bottom of rivers, and is called ground-ice.
Water in ordinary cases freezes at the degree of heat marked 32° on Fahrenheit's thermometer, and 0° on the Centigrade and Reaumur's; but if it is kept perfectly still. it may be cooled to 'nearly 22° F. below freezing, and still remain liquid. The least shake, however, or the throwing in a solid body, makes a portion of it freeze instantly. and its temperature rises immediately to 32°. Sea-water, and salt water in general, freezes at a lewer temperature than pure water; in doing which, part of the salt sepa rates, and the ice, when melted, gives water that is fresher than the original The color of pure ice is deep blue, which is only descernible, however, when it is in large masses. It is best seen in the clefts of a glacier or an iceberg.
In the neighborhood of the poles, and on mountains of a certain height in all latitudes, there exist immense masses of permanent ice; and even in some districts of Siberia. where a kind of culture is practicable in summer, there are found at a certain depth below the surface of the earth strata of ice mingled with sand. In sinking a well at Yakutsk the soil was found frozen hard to the depth of 8S2 ft., and consisting in some parts entirely of lee. These permanent masses of, ice must be classed with rocks and mountains, as among the solid constituents of the globe. In the lower regions of the torrid zone there is no ice, and in the temperate zones, it is a passing phenomenon. From the polar ice-ffelds and glaciers, whicht arc always protruding themselves into the sea. great floating masses become detached, and form icebergs, floes, and drift-he. These bergs or mountains of ice are sometimes more than 250 ft. above the sea-level. They present the appearance of dazzling white chalk-el:ifs of the ffiost fantastic shapes. Fresh fractures have green or blue telor. From the speciAd gravitylt is calculated that the volume of an iceberg below the water is eight times that of the protruding part. Icebergs, and does or ice-fields, are often laden with pieces of rock and massLs
of stones and detritus, which they have brought with them from the coasts liere they were formed, and which they often transport to a great distance towards the equator. These floating masses of ice are dangerous to navigation.
The hardness and Strength of ice increase with the degree of cold. In the severe winter of 1740 a house was built of the ice of the Neva at St. Petersburg IA ft. ion!". 16 whit:, and 20 high, and the walls supported the roof, which was also of ice, without the least injury. Before it stood two ice-mortars and six ice-cannon, made on the turning lathe, with carriages and wheels also of ice. The cannon were of the caliber of 6-pounders, but they were loaded with only lb. of powder, and with hemp-halls—on one occasion with iron. The thickness of the ice was only tour inches, and yet it resisted the explosion.
About 24 years ago Faraday called attention to a remarkable property of ice, since (incorrectly) called regelation. He endeavored to account for the fact that two slabs of ice, with fiat surfaces, placed in contact, unite into one mass when the temperature of the surrounding air is considerably above the freezing-point, by assuming that a small quantity of water, surrounded on every side by ice, has a natural tendency to become ice; and the fact that two blocks of ice placed in contact do not unite unless they arc moist seems to bear out this idea. But J. Thomson gave a totally different explanation of this phenomenon. He showed that the capillary force of the film of water between the plates is sufficient to account for a very considerable pressure between thent; so that from his point of view the phenomenon would be identical with the making of snowballs by pressure; and the formation, by a hydraulic press, of clear blocks front a mass of pounded ice. an observed fact, the explanation of which is to he found in the property of ice mentioned below. See Proceedings ff the Royal Society, 1860-61. Faraday, taking up the question again, showed that the (so-called) regclation takes place in water as readily as in air, a fact quite inconsistent with the action of capillary forces. To this J. Thomson replied, showing, very ingeniously, that the capil lary forces he at first assumed are not necessary to a complete explanation of the observed phenomena. Sec reference above.