Hand book of calculations for engineers and firemen : Relating to the steam engine, the steam boiler, pumps, shafting, etc. . culation of fluids they may abstract heat very quicklyby contact with heated surfaces acting hy convection. Thetable contains the relative conducting powers of metals andearth according to M. Despretz. Relative Lnterxal Conducting Power of Metals. Substance. Relative Conduct-ing Powers. Substance. Relative Conduct-ing Powers. Gold Platinum 1000 981 •Zinc 363 Tin ..... 304 Silver .... 973 iLead 180 Copper Brass 892 ... 749 ! Marble 24 Porcelain 12 Cast Iron 502 Terra Cot
Hand book of calculations for engineers and firemen : Relating to the steam engine, the steam boiler, pumps, shafting, etc. . culation of fluids they may abstract heat very quicklyby contact with heated surfaces acting hy convection. Thetable contains the relative conducting powers of metals andearth according to M. Despretz. Relative Lnterxal Conducting Power of Metals. Substance. Relative Conduct-ing Powers. Substance. Relative Conduct-ing Powers. Gold Platinum 1000 981 •Zinc 363 Tin ..... 304 Silver .... 973 iLead 180 Copper Brass 892 ... 749 ! Marble 24 Porcelain 12 Cast Iron 502 Terra Cotta ... 11 Wrought Iron . 374 CONVECTION OF or carried heat is that which is transferred fromone- place to another by a current of liquid or gas; for example,by the products of combustion in a furnace towards the heatingsurface m the flues of a boiler. THE MECHANICAL THEORY OF and mechan-ical force are identi-cal and of theTried in in throughwhich heat may bedeveloped into me-chanica] action thetame quantity of hen tit ft bo1v< d into ilirtame total quantityof 154 Hand Book of Calculations. THERMO-DYNAMICS. The unit of heat is that which is required to raise 1 lh. ofwater, at 39 degrees Fahr., 1 degree. If 2 lbs. of water beraised 1 degree or 1 lb. be raised 2 degrees in temperature, theexpenditure of heat is the same in amount, namely, two degreesof heat, and to express the mechanical equivalent of heat thecomparison lies between the unit of heat on the one part andthe unit of work—a foot pound—on the other. The most precise determination yet made of the numericalrelation subsisting between heat and mechanical work wasobtained by the following experiment by Dr. Jorles: He con-structed an agitator, Fig. 105 consisting of a vertical shaftcarrying a brass paddlewheel, of which the paddles revolvedbetween stationary vanes, which served to prevent the liquidin the vessel from being bodily whirled in the direction of
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