successive, and only takes place at the surface of contact between the
two gasses. It is quite different when the two gasses are mixed before
they are set on fire: If, for instance, after having introduced one part
of oxygen gas into a narrow mouthed bottle, we fill it up with two
parts of hydrogen gas, and bring a lighted taper, or other burning body,
to the mouth of the bottle, the combustion of the two gasses takes place
instantaneously with a violent explosion. This experiment ought only to
be made in a bottle of very strong green glass, holding not more than a
pint, and wrapped round with twine, otherwise the operator will be
exposed to great danger from the rupture of the bottle, of which the
fragments will be thrown about with great force.
If all that has been related above, concerning the decomposition of
water, be exactly conformable to truth;--if, as I have endeavoured to
prove, that substance be really composed of hydrogen, as its proper
constituent element, combined with oxygen, it ought to follow, that, by
reuniting these two elements together, we should recompose water; and
that this actually happens may be judged of by the following experiment.
_Experiment Fourth._
I took a large cristal baloon, A, Pl. iv. fig. 5. holding about 30
pints, having a large opening, to which was cemented the plate of copper
BC, pierced with four holes, in which four tubes terminate. The first
tube, H h, is intended to be adapted to an air pump, by which the
baloon is to be exhausted of its air. The second tube gg, communicates,
by its extremity MM, with a reservoir of oxygen gas, with which the
baloon is to be filled. The third tube d D d', communicates, by its
extremity d NN, with a reservoir of hydrogen gas. The extremity d' of
this tube terminates in a capillary opening, through which the hydrogen
gas contained in the reservoir is forced, with a moderate degree of
quickness, by the pressure of one or two inches of water. The fourth
tube contains a metallic wire GL, having a knob at its extremity L,
intended for giving an electrical spark from L to d', on purpose to set
fire to the hydrogen gas: This wire is moveable in the tube, that we may
be able to separate the knob L from the extremity d' of the tube D d'.
The three tubes d D d', gg, and H h, are all provided with stop-cocks.
That the hydrogen gas and oxygen gas may be as much as possible deprived
78