$6 Sir H. Davy’s researches on flame. 
fusible metal to heat; and I found that by carefully applying 
a heat between the boiling point of mercury, which is not suf- 
ficient for the effect, and a heat approaching to the greatest 
heat that can be given without making glass luminous in 
darkness, the combination was effected without any violence* 
and without any light: and commencing with 212 0 , the 
volume of steam formed at the point of combination appeared 
exactly equal to that of the original gases. So that the first 
effect in experiments of this kind is an expansion, afterwards 
a contraction, and then the restoration of the primitive 
volume. 
If when this change is going on, the heat be quickly raised 
to redness, an explosion takes place; but with small quanti- 
ties of gas the change is completed in less than a minute. 
It is probable, that the slow combination without combus- 
tion, already long ago observed with respect to hydrogene 
and chlorine, oxygene and metals, will happen at certain 
temperatures with most substances that unite by heat. On 
trying charcoal, I found that at a temperature which appeared 
to be a little above the boiling point of quicksilver, it con- 
verted oxygene pretty rapidly into carbonic acid, without any 
luminous appearance, and at a dull red heat, the elements of 
olefiant gas combined in a similar manner with, oxygene, 
slowly and without explosion. 
The effect of the slow combination of oxygene and hydro- 
gene is not connected with their rarefaction by heat, for I 
found that it took place when the gases were confined in a 
tube by fusible metal rendered solid at its upper surface ; and 
certainly as rapidly, and without any appearance of light. 
M. de Grotthus has stated, that, if a glowing coal be 
