BY HEAT. 23 
pipe. As soon as copper is thoroughly melted (at 
the inner flame), it glows with a greerish-yellow 
light, similar to that of the glow-worm. On cool- 
ing a little,.it rapidly loses this property, and at 
the same time a molecular change is observed on 
the surface of the metal. I have also found that 
the mineral lepidolite is as brilhantly phospho- 
rescent by heat as fluor-spar. But to observe this 
phenomenon properly, it should be viewed through 
a piece of glass-coloured blue by oxide of cobalt. 
In these circumstances, the phosphoric light of 
lepidolite before the blowpipe is very fine. The 
blue glass extmguishes the orange-red light of 
the heated charcoal. | 
Among organic salts it has been observed that 
sulphate of quinine and sulphate of chinconine be- 
come phosphorescent under the influence of heat. 
M. Bottger has remarked that these salts do not 
shine in the dark as long as their temperature con- 
tinues to rise; they become phosphorescent only 
when, after beng heated, the temperature begins 
to decrease and they remain in a luminous state 
for some minutes whilst cooling. Pure quinine 
and sulphate of quinine are very phosphorescent 
in this manner: the phosphoric light given out by 
sulphate of quinine whilst cooling is sufficiently 
strong to enable one to read by it. Pure cincho- 
nine does not appear to be phosphorescent by heat, 
but sulphate of cinchonine is so, though to a less 
degree than sulphate of quinine. 
