these
apartments always in the same invariable order. Suppose further, that,
in preparing yourself for a public discourse, in which you had
occasion to treat of a great variety of particulars, you were anxious
to fix in your memory the order you proposed to observe in the
communication of your ideas. It is evident, that by a proper division
of your subject into heads, and by connecting each head with a
particular apartment, (which you could easily do, by conceiving
yourself to be sitting in the apartment while you were studying the
part of your discourse you mean to connect with it,) the habitual
order in which these apartments occurred to your thoughts, would
present to you in the proper arrangement, and without any effort on
your part, the ideas of which you were to treat. It is also obvious,
that very little practice would enable you to avail yourself of this
contrivance, without any embarrassment or distraction of your
attention.

_To procure Hydrogen Gas._

Provide a phial with a cork stopper, through which is thrust a piece
of tobacco-pipe. Into the phial put a few pieces of zinc, or small
iron nails; on this pour a mixture, of equal parts of sulphuric acid
(oil of vitriol) and water, previously mixed in a tea-cup, to prevent
accidents. Replace the cork stopper, with a piece of tobacco-pipe in
it; the hydrogen gas will then be liberated through the pipe into a
small steam. Apply the flame of a candle or taper to this steam, and
it will immediately take fire, and burn with a clear flame until all
the hydrogen in the phial be exhausted. In this experiment the zinc or
iron, by the action of the acid, becomes oxygenized, and is dissolved,
thus taking the oxygen from the sulphuric acid and water; the hydrogen
(the other constituent part of the water) is thereby liberated, and
ascends.

_To fill a Bladder with Hydrogen Gas._

Apply a bladder, previously wetted and compressed, in order to squeeze
out all the common air, to the piece of tobacco-pipe inserted in the
cork stopper of the phial, (as described in the experiment above.) The
bladder will thus be filled with hydrogen gas.

_Exploding Gas Bubbles._

Adapt the end of a common tobacco-pipe to a bladder filled with
hydrogen gas, and dip the bowl of the pipe into soap-suds, prepared as
if for blowing up soap bubbles; squeeze out small portions of gas from
the bladder into the soap-suds, and the bubbles will ascend into the
air with very great rapidity,