278 Mr. T. Wedgwood^s Experiments and Observations 
was cold, I stuck a few grains of gunpowder upon its surface, and 
looking within the tube, fired them by pressing them against a 
hot iron, but the light of tie explosions was not then sensible. 
Plates of silver, and of iron, gave the same results. 
EXPERIMENT X. 
A lump of the most luminous marble, and an equal lump of 
the same marble blackened over, were placed together upon a 
mass of iron heated just under redness : the former gave out 
much light, the latter none. Upon a second exposure, the 
lump not blackened gave a faint light ; the blackened one, as 
before, none at all. Then wiping off the black, and placing 
them together upon the heater, I found the one which had 
been blackened to emit as little light as the other : thus the 
phosphorescent property was nearly destroyed, without any 
visible light leaving the body. 
EXPERIMENT XI. 
If a piece of glass, or glazed or unglazed earthen ware, with 
any enamel, painting, gilding, or writing in ink upon it, be 
made red hot, the coloured parts appear considerably more red 
than the others, and continue longer visible. Iron wire, within 
a red hot glass tube, looks much more red than the glass. Black 
matter, upon a large polished mass of fine gold, did not re- 
main any longer red than the gold. 
EXPERIMENT XII. 
A bit of iron wire becomes visibly red hot when immersed 
in melted glass. Air, therefore, is not necessary to the shining 
of ignited bodies. 
