10 Some new Researches on Flame. 
I made several other experiments which establish the same con= 
elusions. A mixture of common air and hydrogen was intro- 
duced into a small copper tube, having a stopper not quite tight 
the copper tube was placed in a charcoal fire: before it beeame 
visibly red an explosion took place, and the stopper was driven 
out. 
I made various experiments on explosions by passing mixtures 
of hydrogen and oxygen through heated tubes: in the beginning 
of one of these trials, in which the heat was much below redness, 
steam appeared to be formed without any combustion. This led 
me to expose mixtures of oxygen and hydrogen in tubes, in which 
they were confined by fluid fusible metal to heat; and I found 
that by carefully applying a heat between the boiling point of 
mercury, which is not sufficient for the effect, and a heat ap- 
proaching 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°, 
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 quantities of 
gas the change is completed in less than a minnie. 
It is probable, that the slow combination without combustion, 
already long ago observed with respect to hydrogen and chlorine, 
oxygen 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 converted oxygen pretty rapidly 
into carbonic acid, without any luminous appearance, and ata 
dull red heat, the elements of olefiant gas combined in a similar 
manner with oxygen, slowly and without explosion. 
The effect of the slow combination of oxygen and hydrogen 
is not connected with their rarefaction by heat, for J 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 brought 
into contact with a mixture of oxygen and hydrogen, it only 
rarefies them, but does not explode them; but this depends 
upon the degree of heat communicated by the coal: if it is red 
in day-light and free from ashes, it uniformly explodes the mix- 
ture; if its redness is barely visible in shade, it will not explode 
them, but cause their slow combination: and the general phe- 
nomenon is wholly unconnected with rarefaction, as is shown by 
the 
