Heat is a peculiar motion of the particles of matter which prevents their contact. Heat and mechanical power are convertible forms of energy. The energy of the heat that raises one pound of water 1° F. will lift a weight of 778 lbs. one foot. The power of a weight of 778 lbs. descending one foot, if applied to a small paddle wheel turning in one pound of water, will, by friction, raise the temperature of the water 1° F.

A heat-unit is the amount of heat that raises a pound of water 1° F., or that lifts a weight of 778 lbs. one foot.

The mechanical equivalent of a heat-unit is the power of a weight of 778 lbs. descending one foot, or of a one-pound weight descending 778 feet. Hence,

778 foot-pounds = 1 heat-unit. 1 heat-unit = 778 foot-pounds.

A galvanic battery that produces an electrical current capable of heating one pound of water 1° F., will yield magnetic force sufficient to raise a weight of 778 lbs. one foot high.

Thus heat, electricity, magnetism, and chemical force are brought into numerical correlation with mechanical power.

The illustrious philosopher, Dr. J. P. Joule, of Manchester, England, first measured accurately the mechanical equivalent of heat, a.d. 1845.

## Heat Of Metals

A metal is an element possessing a luster, and the higher oxides of which only are acid-forming compounds. Metals have the following properties: A specific gravity usually greater than one. The specific heat is less than unity, and this heat varies inversely as the atomic weight of that element. The conductivity of the metals is greater than that of either the non-metals or their compounds.

The influence of heat upon metals is very varied; some melt at a low temperature, others require a red heat, a strong red, or a white heat respectively, to melt them. The following table, by Pouillet, will explain the temperatures corresponding to different colors:

 Heat Color. Corresponds to Incipient red heat. . . 525° C. 977° F. Dull red............. 700 1,292 Incipient cherry red. . . 800 1,472 Cherry red........... 900 1,652 Clear Cherry red 1,000 1,832 Deep orange 1,100 2,012 Clear orange 1,200 2,192 White............... 1,300 2,372 Bright white.......... 1,400 2,552 Dazzling white..... . . 1,500 2,732