\ 
8 Sir Humphry Davy on the fire-damp of coal mines, and on 
visible heat of iron and charcoal ; and the case is the same 
with sulphuretted hydrogene. 
I endeavoured to ascertain the degree of expansion of 
mixtures of fire-damp and air during their explosion, and 
likewise their power of communicating flame through 
apertures to other explosive mixtures. 
I found that when 6 of air and 1 of fire-damp were 
exploded over water by a strong electrical spark, the explo- 
sion was not very strong, and, at the moment of the greatest 
expansion, the volume of the gas did not appear to be in- 
creased more than 
In exploding a mixture of 1 part of gas from the distilla- 
tion of coal, and 8 parts of air in a tube of a quarter of an 
inch in diameter and a foot long, more than a second was 
required before the flame reached from one end of the tube 
to the other; and I could not make any mixture explode in a 
glass tube -j of an inch in diameter : and this gas was more 
inflammable than the fire-damp, as it consisted of carburetted 
hydrogene gas mixed with some olefiant gas. 
In exploding mixtures of fire-damp and air in a jar con- 
nected with the atmosphere by an aperture of half an inch, 
and connected with a bladder by a stopcock, having an aper- 
ture of about i of an inch,* I found that the flame passed into 
the atmosphere, but did not communicate through the stop- 
cock, so as to inflame the mixture in the bladder : and in com- 
paring the power of tubes of metal and those of glass, it 
appeared that the flame passed more readily through glass 
tubes of the same diameter; and that explosions were stopped 
* Since these experiments were made. Dr. Wollaston has informed me, that he 
and Mr. Tennant had observed some time ago, that mixtures of the gas from th§ 
distillation of coal and air, would not explode in very small tubes. 
