This molecular work is that which has usually been called _specific heat_, or _capacity for heat_. According to the _materialistic_ view of heat, bodies are figured as sponges, and heat as a kind of fluid absorbed by them, different bodies possessing different powers of absorption. According to the _dynamic_ view, as already explained, heat is regarded as a motion, and capacity for heat indicates the quantity of that motion consumed in internal changes. The greatest of these changes occurs when a body passes from one state of aggregation to another, from the solid to the liquid, or from the liquid to the aeriform state; and the quantity of heat required for such changes is often enormous. To convert a pound of ice at 32 deg. Fahr. into water _at the same temperature_ would require an amount of heat competent, if applied as mechanical force, to lift the same pound of ice to a height of 110,000 feet; it would raise a ton of ice nearly 50 feet, or it would lift between 49 and 50 tons to a height of one foot above the earth's surface. To convert a pound of water at 212 deg. into a pound of steam at the same temperature would require an amount of heat which would perform nearly seven times the amount of mechanical work just mentioned. [Sidenote: HEAT CONSUMED IN MOLECULAR WORK.] This heat is entirely expended in _interior work_,[A] and does nothing towards augmenting the temperature; the water is at the temperature of the ice which produced it, both are 32 deg.; and the steam is at the temperature of the water which produced it, both are 212 deg. The whole of the heat is consumed in producing the change of aggregation; I say "_consumed_," not hidden or "latent" in either the water or the steam, but absolutely non-existent as heat. The molecular forces, however, which the heat has sacrificed itself to overcome are able to reproduce it; the water in freezing and the steam in condensing give out the exact amount of heat which they consumed when the change of aggregation was in the opposite direction. At a temperature of several degrees below its freezing point ice is much harder than at 32 deg. I have more than once cooled a sphere of the substance in a bath of solid carbonic acid and ether to a temperature of 100 deg. below the freezing point. During the time of cooling the ice crackled audibly from its contraction, and afterwards it quite resisted the edge of a knife; while at 32 deg. it may be cut or crushed with extreme facility. The cold sphere was subjected to pressure; it broke with the detonation of a vitreous body, and was taken from the press a white opaque powder; which, on being subsequently raised to 32 deg. and again compressed, was converted into a pellucid slab of ice. [Sidenote: ICE NEAR THE MELTING POINT.]