INTRODUCTION. 7 



where they take part in conduction; a "liquid" state where there is a state 

 of motion sensitive to light vibrations; and a "solid" state where the elec- 

 trons take part in neither conduction nor the absorption of light. They 

 consider that in the states of aggregation which cause phosphorescent bands 

 there are certain places in the atoms, dynamids, where electrons can be 

 stored at low temperatures. To each phosphorescent band there correspond 

 then these phases: (1) an upper momentary or heat phase; (2) a perma- 

 nent phase; and (3) a lower momentary phase. For a great many bands 

 they succeed in obtaining these three phases when they change the tempera- 

 ture sufficiently. The temperature of solid hydrogen is sufficiently low to 

 bring most of the phosphorescent bands into the lower momentary phase. 

 In this phase the electrons ejected from the metallic atom by photoelectric 

 influence of illumination are fixed and stored in the neighborhood, only a 

 few returning immediately, and these produce the "momentary light" 

 observed during illumination. In the permanent phase the electrons are 

 stored for a certain time in the dynamids and eventually return to the 

 metallic atom. 



Various theories have been proposed to explain the more or less general 

 absorption throughout large regions of the spectrum. Drude l considers 

 that in general ultra-violet bands are due to the absorption of electrons, 

 and infra-red bands to the absorption of ions. Houstoun, 2 Pfund, 3 and 

 others support this view. 



(c) BANDED SPECTRA. 



By banded spectra we shall in general designate bands which at low 

 temperatures become quite fine, such as the uranyl, neodymium, or erbium 

 bands. As the present paper deals with only a small range of temperature 

 and concentration and but one solvent, a full review of previous work will 

 not yet be given. Rudorf and Washburn have given a very good review 

 of this subject from the hydrate point of view. 



Brewster observed, in 1831, that the transparency and color of many 

 solids change when they are heated. Schonbein, in 1852, states that many 

 bodies become more highly colored at higher temperatures while at low 

 temperatures they lose their color. He found that sulphur is colorless at 

 50 C. and bromine at 70 C. Moissan and Dewar, in 1903, found that 

 fluorine becomes colorless at 253, so that at low temperatures chlorine, 

 bromine, iodine, and fluorine are colorless. 



Conroy (1891) found that the bands of cobalt glass are displaced 

 towards the red with rise in temperature. Rizzo (1891) found similar 

 results with glasses containing cobalt, didymium, and manganese. Konigs- 

 berger (1901) found the curve of absorption to be displaced towards the red 

 with rise in temperature, but concluded that the maximum of absorption 

 was not changed. This applied to the wider bands. The fine bands showed 

 no displacement between 10 and 500 C. Hartley investigated the absorp- 

 tion spectra of a large number of solutions between and 100. He inter- 



1 Ann. Phys., 14, 677-725, 936-961 (1904). 

 * Proc. Roy. Soc, 606 (1909). 

 3 Astrophys. Journ., 24, 19 (1906). 



