Page:Popular Science Monthly Volume 83.djvu/251

Rh salt and acid. Evidences of series of "aggregates" were obtained by spectrophotographs of chemical reactions, spectrograms of the absorption spectra of a solution of a given salt being taken as increasing amounts of some other kind of acid was added to the solution.

Lenard, Klatt, Urbain and others have studied the phosphorescence of various calcium phosphates of bismuth, manganese, nickel, etc. Lenard and Klatt have proposed the view that these light centers or "dynamids" store electrons, the state of motion of the electrons depending upon the temperature. At high temperatures the electrons possess a much greater freedom of motion than at low temperatures. They visualize the states of motion as being "gaseous," "liquid" and "solid." In the "gaseous" state the electrons can occasion the conduction of electricity between the atoms if the latter exist in the same way as they do in metals. In the "liquid" state the electrons are in a state of motion sensitive to light vibrations and therefore they take part in light absorption. In the "solid" state the electrons take part neither in conduction nor in absorption. At low temperatures the spheres of action of the "dynamids" are considered to extend to greater distances than at high temperatures and the free paths of the electrons are therefore greatly reduced.

To each phosphorescent band Lenard and Klatt assign three phases: An upper momentary or heat phase; a permanenntpermanent [sic] phase possessing quite definite temperature limits; and a lower momentary or cold phase. These phases succeed each other as the temperature falls. The upper momentary phase results when the dynamids do not store electrons. Whenever electrons are stored these return afterwards to the atom from which they were expelled by the light-wave, thus producing the permanent phase of the phosphorescent band. At low temperatures a few electrons return to the atoms from which they were expelled and these cause the lower momentary phase.

The phenomena of phosphorescence are generally conceded to be due to some kind of electrolytic dissociation or ionization of the dissolved substance in the medium about it. Among the first to hold this view were Wiedeman and Schmidt. The theory explains the law of Stokes and many of the other phenomena of phosphorescence.

During recent years a very large number of investigations have been carried out concerning the nature of the absorption light centers of organic compounds, both pure and in a state of solution. These centers have been roughly defined as chromophores, the chromophores consistinoof radicles of the given compounds that are found necessary and sufficient to produce the given absorption. Among the chromophores that