. The railroad and engineering journal . , yet if we attached a thermometer to the dropwe would not find that it was any warmer than before the drop was raised. If it were possible to make an instrument suffic-iently sensitive to indicate an instantaneous change of tem-perature in the weight while falling, we would not find any in-crease of its temperature at the instant it had acquired its . greatest momentum and just before it struck the object underit, although its potential energy would at that instant be con-verted into actual energy of motion. If, however, the weightshould strike an unyi
. The railroad and engineering journal . , yet if we attached a thermometer to the dropwe would not find that it was any warmer than before the drop was raised. If it were possible to make an instrument suffic-iently sensitive to indicate an instantaneous change of tem-perature in the weight while falling, we would not find any in-crease of its temperature at the instant it had acquired its . greatest momentum and just before it struck the object underit, although its potential energy would at that instant be con-verted into actual energy of motion. If, however, the weightshould strike an unyielding object, its actual energy would atonce be reconverted into heat, which our thermometer wouldindicate. The phenomenon of what is called latent heat ofevaporation seems to be very similar to that described—the heat when the water is changed from a liquid to a gaseouscondition is transformed into energy, which, as already stated,( has no effect upon the mercury of the thermometer. 1 * Balfour Stewart on the Conservation of ol. LXI, No. II.] ENGINEERING JOURNAL. 526 Question 62. llAat is meant 6y the total ukat of steam ? Answer. The total heat of steam is a phrase used todenote the sum of the heat required to raise the temperatureof water from some given point up to the boiling-point due toa given pressure, and of the heat which disappears in evap-orating one pound of water under a given pressure (or latentheat of e^iaporatioii). Thus, the latent heat of one pound ofsteam at atmospheric pressure ( lbs.) is g66. i units; and212 units of heat arc necessary to raise water from zero to theboiling-point ; therefore, the total heat counted from zero ofsteam of atmospheric pressure is 1, units. At 100pounds absolute pressure the latent heat is and hesensible heat 327. tj degrees ; therefore the total heat measuredfrom zero is 1, units. CHAPTER STEAM ENGINE. blQuESTlON 63. What is the motive power employfd in nn/imuvsteam engines? Answer. The e
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