Page:International Library of Technology, Volume 93.djvu/59

 is expelled, and then tightly corked and inverted, the boiling will of course stop; but if a little cold water is poured over the flask as shown, to condense the steam, the water will begin to boil again by reason of the reduction in pressure, due to the condensation of the vapor in the top of the flask. It will continue to boil until the establishment of equilibrium causes it to stop; but it may again be started boiling by pouring more water over the flask in the same way. In this manner, the boiling may be kept up until the water has reached the temperature of the room. If a quantity, of water is boiling under high pressure and the pressure is suddenly reduced, a portion of the water will pass instantly into steam, abstracting heat from the remainder of the water as it does so, until the temperature is lowered to that corresponding to the pressure on the water.

57. By the total heat of saturated steam at any given temperature is meant the amount of heat required, first, to raise the temperature of the water from the freezing point to that temperature; and, secondly, to convert it into steam at that temperature and corresponding pressure. As the pressure and the temperature increase, the latent heat of steam is found to diminish slightly, but this is more than compensated for by the added heat required to raise the temperature of the water to the higher boiling point; so that the total heat absorbed increases slightly as the pressure and temperature increase.

58. If balls of iron, zinc, copper, lead, and tin, of equal weights, are exposed to heat for a short, but equal, length of time, as by being arranged in a row before an open fire, it