ICE 108 ICE, ARTIFICIAL Water in ordinary cases freezes at the degree of temperature marked 0° on the Centigrade and Reaumur's thermometers and 32° on Fahrenheit's, but if it is kept perfectly still it may be cooled to nearly 5.5° C. below freezing (22° F.) and still remain liquid. Sea-water, and salt water in general, freezes at a lower tem- perature than pure water; in doing this, part of the salt separates, and the ice when melted, gives water that is fresher than that on which the ice was formed. In the neighborhood of the poles, and on mountains of a certain height in all lati- tudes, there exist immense masses of per- manent ice ; and even in some districts of Siberia, where a kind of culture is prac- ticable in summer, there are found, at a certain depth below the surface of the earth, strata of ice, mingled with sand. Nansen and Peary discovered that the entire surface of Greenland, except the mountainous coasts, is covered with the largest ice-cap known to exist, having a supposed depth of several thousand feet. The W. coast of Greenland produces most of the icebergs that float in the North Atlantic. From the polar icefields and glaciers which are always protruding themselves into the sea, great floating masses become detached and form ice- bergs, floes, and drift ice (see Glacier). From the specific gravity it is calculated that the volume of an iceberg below the water is about nine times that of the pro- truding part. The trade in ice is now one of great and increasing importance. Ice has come to be more and more largely used in preserving provisions, both in refrig- erating chambers and otherwise. In sur- gical operations it is used to produce partial anaesthesia; it serves in fevers to cool the mouth and reduce the internal temperature, while ice in bags, applied to the spine, is found helpful in many cases of sea-sickness and in other appli- cations. In 1799 the first cargo of ice was sent from New York to Charleston, and ice was imported into England from Norway on a considerable scale as early as 1823. The export of ice from the United States was begun about 1805 by a merchant named Tudor, who sent ice from Boston to the West Indies. After persevering against many losses he suc- ceeded in 1833 in establishing a trade with Calcutta, Madras, and Bombay; and now not only is it sent in vast quantities to these places, but also Hong Kong and Batavia. Triest sends ice to Egypt, Corfu, and Zante; Switzerland sends it to France, and Germany sometimes gets her supply from the Bavarian lakes. In the United States the ice harvest is gathered in on an enormous scale and with an elaborate system of apparatus. The ice is cleared from snow by means of an implement called the snow-plane. An ice-plow, drawn by horses, and driven by a man riding on it, or propelled by steam, is then made to cut deep parallel grooves in the ice, and these are again crossed by other grooves at right angles, so that the whole of the surface is deeply marked out into small squares measuring a little more than three feet. A few of these square blocks being de- tached by handsaws, the remainder are easily broken off with crowbars, and floated away to the ice-storehouses, which are usually built of wood, on the borders of the lake or river. The blocks of ice are covered up with sawdust, a layer being placed between each tier of blocks. Many of these ice-houses are made large enough to hold from 40,000 to 80,000 tons of ice. Throughout the States, ex- cept in the extreme N., the manufacture of artificial ice is extensively carried on. The building of ice-edifices was, and perhaps still is, a winter amusement in Russia; and in the New World, Montreal sets the example of an annual ice-carni- val, one of the features of which is the building of a great ice-palace, and of ice- monuments of various kinds, ICE, ARTIFICIAL, ice frozen by me- chanical or chemical means. It has the great advantage of being easily rendered chemically pure, and it can be manu- factured in the hottest countries. Its commercial value in the preservation and transportation of meats, fruits, etc., and for other purposes, can scarcely be esti- mated. The water is first boiled and allowed to settle. It is then distilled, boiled again and run through three kinds of filters. Underneath the great square middle space of the freezing room, which is paved with large rectangular remov- able tiles, is a series of tanks. These contain a strong solution of brine, and through it run scores of pipes which are charged with liquefied ammonia gas. When this volatile chemical leaves the engine room it is in the form of a fluid, but in making its long journey along the pipes which thread their way through the brine it evaporates into gas. The evaporating process within ab- sorbs so much heat from the surrounding mass of salt and water that the distilled water in the rectangular ice cans sub- merged in the brine is congealed into the finest ice. Each can contains 300 pounds of distilled water, which remains in its cold bath 48 hours. Natural gas is often employed in the process of manu- facturing artificial ice. As it escapes from the borings with a pressure of 20 to
