i 174) 
influence, not as free electrons, but by anions, and it must then be 
assumed of this kind of neutralisation, that it is not accompanied by 
emission of light. If the “phosphor” is in a medium containing mam- 
free electrons, such as e. g. a flame *), then it appears to be able 
to phosphoresce far above that temperature limit; it lights up of 
its own accord with the phosphorescence colour belonging to this 
temperature, while light at this temperature is not necessary to 
induce phosphorescence, and indeed could not do so. To this group 
of phenomena also belongs that described in “1904” of the “phos¬ 
phors” lighting up with colours, when after being freshly prepared 
and still glowing with heat, they are crushed by pressure. In that 
case there always occurs a burning of the sulphur from the “phosphor” 
by contact with the air; in fact this glow is seen only where fresh 
cleavage surfaces formed in the crushing come in contact with the air, 
and there also small sulphur flames are often to be seen. If too rapid 
cooling is prevented, addition of oxygen increases the glow. If the 
“phosphor” is too cold to show the phenomenon of the burning 
away of the sulphur, then also breakage causes no glow. 
On the other hand by holding it on a platinum wire in a flame 
one can easily keep a piece of “phosphor” — e.g. CaBiNaor 
Sr Bi Na — that has not previously been under the influence of 
glowing for a long time with its phosphorescence colour (heat 
band) at a red heat, and therefore above the temperature limit at 
which it could be excited by light. The flame must be poor in 
oxygen if the phenomenon is to last, for as soon as the “phosphor” 
is deprived of sulphur by burning, the glowing ceases. 
We further remark that according to the theory above developed 
the upper temperature limit of phosphorescence excited by light 
seems to be a consequence of the electrolytic dissociation of the 
material of the “phosphor”, while its entering the upper momentary 
phase — which happens for the different bands even of the same 
“phosphor” at such widely differing temperatures, e.g. a little above 
— 180°C. for CaBiy, and at + 450° C. for CaBi/J — can depend 
only upon processes within the corresponding centrum, that is to 
say, upon the rendering of electrons from the place where they have 
been stored in the centrum occurring at temperatures differing widely 
according to the nature of the centrum. 
J ) P. Lenard, Ann. d. Pftys. 9. p. 649 1902. 
