ICE AND REFRIGERATION Nature of Ice.—Ice is one of a number of substances that occupy a greater volume in the solid than in the liquid state. At the moment of freezing it expands with great force about one eleventh in bulk, as is testi fied by the bursting of frozen water pipes.
An interesting experiment consists in passing a wire through a solid block of ice without cutting it in two. The ice should be supported at both ends, leaving the middle free, and the wire over it with weights attached to either end. The pressure on the wire raises the temperature of the ice to the melting point and allows the wire to sink; but the wire absorbs some of the heat, and causes the water to freeze upon its upper surface; hence the seam is closed, and after the pas sage of the wire the block of ice re mains intact. Its course, however, can be traced by the air bubbles which it leaves behind.
Under ordinary conditions water freezes at 32° F., and does not melt until the temperature is raised above that point; but under pressure, as above noted, ice will be converted into water at a lower temperature, having been melted under high pressure at 18° C. If water is perfectly still it may be lowered to 22° F. before freez ing, but the slightest jar will cause it to freeze when the temperature rises to 3.3° F.
Uses of Ice.—In addition to its nat ural service in transforming lakes and rivers during winter in northern cli mates into solid roadways, ice is in great demand as an antiseptic or pre serving agent. Formerly it was sup posed that meats and carcases of ani mals intended for food must be frozen to be preserved. The discovery of the practicability of preserving meats and vegetables by means of ice, but with out freezing them, is comparatively recent. Now, in addition to the house hold refrigerator, refrigerating cars convey beef, fruit, and vegetables across continents, and refrigerating steamships take tropical fruits and other products from southern to north ern climes and return with dairy products, northern fruits, and other perishable articles that could not otherwise be obtained in tropical coun tries. In many cities cold-storage houses also preserve, with a very slight percentage of loss, dairy products, meats, fruits, and vegetables for pe riods varying from months to years.
Cold-storage vaults protect furs and valuable garments from the ravages of moths and other insects. Ice is also now regarded as absolutely necessary in the summer months to preserve the bodies of the dead until the time of burial.
To Harvest Commercial Ice. — Ice has been an important article of com merce since the time of Nero, and in cold countries family ice houses are very common. Sometimes these stor age places are merely pits or caves under ground, or partly under ground, but an ice house wholly above ground is to be preferred.
Ice from salt or brackish water is nearly pure, as freezing expels the mineral ingredients, but it is suffi ciently contaminated on the surface to be unfit for many purposes. Hence the best ice crop is' usually gathered from fresh-water ponds, or lakes, or in rivers above tide water. A great deal of ice is also manufactured arti ficially. Commercial ice houses are usually built of wood, having hollow walls that may be double, triple, or quadruple, the spaces between being filled with sawdust, spent tan bark, or some other poor conductor of heat.
In harvesting ice the usual practice is to scrape the snow from the surface of the ice by means of a scraper drawn by horses, to plane off the soft porous top of the ice if necessary by means of a horse planer, and to mark the ice into blocks by running a series of grooves about 5 feet apart and 3 inches deep so as to make blocks 5 feet square. Ice is usually cut when it is about 2 feet thick. After the ice has been marked one row of blocks is usually cut through by means of a handsaw, and pushed under out of the way or pulled up on the ice. The succeeding blocks are pried off with a crowbar, towed to the landing place, and loaded into wagons or run up an inclined plane to the storehouse and packed away. The blocks are stood on end in a solid mass. A space is left between the ice and the walls of the ice house in which are gutters and drainways to receive and carry off the drainage from the melted ice.