376 THE POPULAR SCIENCE MONTHLY. 



rushes in to form new compounds; the oxygen-atom, by its impact upon 

 the coal, has its motion of translation converted into vibratory motion, 

 which immediately appears as heat. The clash of these atoms makes 

 up the sum total of the energies of the combustion. The actual amount 

 of dynamical energy set free by the union of this pound of charcoal 

 with atmospheric oxygen is equivalent to the mechanical raising of 

 eleven and a quarter million pounds one foot high. Let us further con- 

 sider the dynamical forces inherent in the molecules of free gases, and 

 look to a molecular explanation of the three states of matter, the solid, 

 fluid, and gaseous. In solids the atoms are held together with a rigid- 

 ity that develops the full strength of cohesive force. In liquids the 

 same attraction is so far lessened that a definite form can only be pre- 

 served in a limited degree, as in drops of water maintaining a spheroidal, 

 shape against the force of gravity. In the gaseous form atoms do not 

 cohere, the cohesive force having been translated into the energy of 

 motion, and it is this energy of motion which constitutes the expansive 

 force of confined gases. 



Suppose we have a vessel containing eight pounds of oxygen and one 

 pound of hydrogen. This mechanical mixture of gases, invisible though 

 it be, and harmless as it appears, is the theatre of energies wholly beyond 

 our conceptions. Figure to your imagination these gases made up of 

 atoms so small that a billion times a billion would scarcel}'^ fill a cubic 

 inch, and all these atoms vibrating among themselves without actual 

 contact. Although the minute distances over which these atoms travel 

 are utterly immeasurable by direct appliances, we shall presently see that 

 the energies evolved by the clash of their chemical union is something 

 prodigious. The concussion of atoms at the union of eight pounds of 

 oxygen with one pound of hydrogen sets free an amount of energy, in 

 the form of heat, equivalent in mechanical value to 47,246,400 pounds 

 let fall one foot, or the crash of a ton's weight as an avalanche down a 

 precipice of 23,623 feet. 



The three states of matter have been likened to three planes, of 

 which the gaseous is the uppermost, the fluid occupying the interme- 

 diate plane, and the solid state for the lower one. The clash of atoms 

 at the union of the two gases has resulted in the liberation of the ener- 

 gy above mentioned, but a change of state has taken place, and we now 

 have water in the vaporous condition occujDying the intermediate plane. 

 This nine pounds of steam in condensing to water sets free an energy, the 

 mechanical equivalent of 6,722,000 pounds let fall through the space of 

 one foot. The next change takes us past the reduction of the temper- 

 ature of the water from the boiling to the freezing point, setting free 

 both the specific and latent heat of the water. This final fall to the 

 plane of congelation occasions a further dissipation of energy equiva- 

 lent to 2,237,256 foot-pounds, making a grand total of 56,000,000 foot- 

 pounds as the measure of energy in our nine pounds of invisible gas. 



The verity of these statements might be questioned were it not that 



