e. 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
of water, they are made to pass, in their way to the baloon A, through
the tubes MM, NN, of about an inch diameter, and filled with salts,
which, from their deliquescent nature, greedily attract the moisture of
the air: Such are the acetite of potash, and the muriat or nitrat of
lime[18]. These salts must only be reduced to a coarse powder, lest
they run into lumps, and prevent the gasses from geting through their
interstices.

We must be provided before hand with a sufficient quantity of oxygen
gas, carefully purified from all admixture of carbonic acid, by long
contact with a solution of potash[19].

We must likewise have a double quantity of hydrogen gas, carefully
purified in the same manner by long contact with a solution of potash in
water. The best way of obtaining this gas free from mixture is, by
decomposing water with very pure soft iron, as directed in Exp. 3. of
this chapter.

Having adjusted every thing properly, as above directed, the tube H h is
adapted to an air-pump, and the baloon A is exhausted of its air. We
next admit the oxygen gas so as to fill the baloon, and then, by means
of pressure, as is before mentioned, force a small stream of hydrogen
gas through its tube D d', which we immediately set on fire by an
electric spark. By means of the above described apparatus, we can
continue the mutual combustion of these two gasses for a long time, as
we have the power of supplying them to the baloon from their reservoirs,
in