SUMMATION AND RECAPITULATION.
I. Molecules and crystals may in many ways be considered as identical.
-
They have definite form and are bound together by valence forces which cannot be explained otherwise than as directed forces.
-
That compounds may be classified as exothermic and endothermic, depending on whether energy is absorbed or released when the valence bonds are broken.
-
The condition of the endothermic compound is best described by assuming that the valence bonds are bent away from their natural direction with a resulting strain within the molecule or cry. stal. These compounds have within themselves a force tending to self-destruction. One compound may have both endothermic and exothermic bonds.
-
The form and the other properties of a compound are interdependent. The destruction of the form simultaneously destroys all of the properties, or the compound itself.
-
Crystals may be mechanically stressed to the point of rupture.
-
Crystals break under stresses which are only a small percentage of the theoretically calculated requirements.
-
Most crystals found in nature are imperfect. 9. Crystals have fissures or small cracks, in their surfaces, which is the probable cause of their low actual strength.
IO. The surfaces of all crystals are unsaturated. The surface cracks or fissures are probably caused by the unsaturated condition or surface tension. I I. Strains in crystals disappear with the velocity of sound upon the release of stresses.
,355 * Reference should be made to the words of Jones at this point, "Then with a compression in front of it and a rarifaction behind it the layer of air is brought to rest and may even be started to move backwards."
* "Probably the majority of chemical reactions, even those which eventually lead to the evolution of large amounts of energy, require some initial excitation of the molecule, and it undoubtedly frequently happens that a system must be lifted far above its original energy level before it can fall into a still lower energy level." "Valence and the Structure of Atoms and Molecules," Lewis, page I6o, Reinhold Publishing Co., N. Y.