I 
45 ^ Count Rum ford's Inquiry concerning the 
to be more explicit, by exposing the oxide in a certain tempe- 
rature, at which it becomes disposed to vitrify, or to undergo 
a change in regard to the quantity of oxygen with which it is 
combined ? 
But the results of the following experiments afford still 
more satisfactory information, respecting the intensity of the 
heat generated in all cases where light is absorbed, and the 
striking effects which, under certain circumstances, it is ca- 
pable of producing. 
The facility with which most of the metallic oxides are re- 
duced, in the dry way, by means of charcoal, shows that, at a 
certain (high) temperature, oxygen is disposed to quit those 
metals, in order to form a chemical union with the charcoal, 
or at least with some one of its constituent principles, if it be 
a compound substance ; and hence I concluded, that gold might 
be revived, in the moist way, by means of charcoal, from a solu- 
tion of its oxide in water, were it possible, under such circum- 
stances, to communicate to the charcoal, and to the oxide, at 
the same time, a degree of heat sufficient for that purpose. 
To see if this might not be done by means of light, I made, 
or rather repeated, the following very interesting experiment. 
Experiment No. q. Into a thin tube of very fine colourless 
glass, 10 inches long, and -jo °f an inch in diameter, closed 
hermetically at its lower end, I put as many pieces of charcoal, 
about the size of large peas, as filled the tube to the height of 
two inches; and, having poured on them as much of the aqueous 
solution of nitro-muriate of gold as nearly covered them, ex- 
posed the tube, with its contents, to the action of the direct rays 
of a very bright sun. 
In less than half an hour, small specks of revived gold, in all 
