Water in a solid, crystallized state, owing to the abstraction of its combined heat. Its specific gravity, according to Dr. Thomson, is .92. The force of expansion exerted by water in the act of freezing has been found irresistible in all mechanical experiments to prevent it. Advantage of this wonderful phenomenon is taken to burst bomb shells, and other massive vessels, by filling them with water, plugging them up, and then exposing them to the frost. The effects of this expansive force are often observable by the bursting of trees, and the rending of rocks, attended with a noise resembling the explosion of confined gunpowder. Water after being long kept boiling, affords an ice more solid, and with fewer air bubbles, than that which is formed from unboiled water; also pure water, kept for a long time in vacuo, and afterwards frozen there, freezes, much sooner than common water exposed to the same degree of cold in the open atmosphere; and the ice formed of water thus divested of its air, is much more liard, solid, heavy, and transparent, than common ice.

Ice after it is formed, continues to expand by decrease of temperature; to which fact is probably attributable the occasional splitting and breaking up of the ice of ponds during the time of freezing, and sometimes, independent of other causes, the separation of icebergs from the great frozen continent at the poles. According to Dr. Black, ice requires 147 degrees of heat to reduce it to a fluid.