(99.)

It has been explained, that to effect the conversion of water into steam, it is only necessary to impart to it as much heat as, added to the temperature which it has, would, if it continued in the liquid form, raise it to the temperature of 1212°. This condition is necessary, and sufficient to effect the transition of water into vapour. If, for example, as much heat were imparted to the water evaporated, as would maintain it in the liquid state to 1300°, then the steam so produced would be superheated steam, having 80° of heat more than is necessary to maintain it in the vaporous form. From such steam, therefore, 80° of heat may be abstracted without producing any condensation. [Pg173]