hydrogen here with which we can charge this balloon made of collodion. I
need not even be very careful to get all the air out, for I know the power
of this gas to carry it up. [Two collodion balloons were inflated, and
sent up, one being held by a string.] Here is another larger one made of
thin membrane, which we will fill and allow to ascend. You will see they
will all remain floating about until the gas escapes.
What, then, are the comparative weights of these substances? I have a
table here which will shew you the proportion which their weights bear to
each other. I have taken a pint and a cubic foot as the measures, and have
placed opposite to them the respective figures. A pint measure of this
hydrogen weighs three-quarters of our smallest weight (a grain), and a
cubic foot weighs one-twelfth of an ounce; whereas a pint of water weighs
8,750 grains, and a cubic foot of water weighs almost 1,000 ounces. You
see, therefore, what a vast difference there is between the weight of a
cubic foot of water and a cubic foot of hydrogen.
Hydrogen gives rise to no substance that can become solid, either during
combustion or afterwards as a product of its combustion. But when it
burns, it produces water only; and if we take a cold glass and put it over
the flame, it becomes damp, and you have water, produced immediately in
appreciable quantity; and nothing is produced by its combustion but the
same water which you have seen the flame of the candle produce. It is
important to remember that this hydrogen is the only thing in nature which
furnishes water as the sole product of combustion.
And now we must endeavour to find some additional proof of the general
character and composition of water; and for this purpose I will keep you a
little longer, so that at our next meeting we may be better prepared for
the subject. We have the power of arranging the zinc which you have seen
acting upon the water by the assistance of an acid, in such a manner as to
cause all the power to be evolved in the place where we require it I have
behind me a voltaic pile, and I am just about to shew you, at the end of
this lecture, its character and power, that you may see what we shall have
to deal with when next we meet. I hold here the extremities of the wires
which transport the power from behind me, and which I shall cause to act
on the water.
We have previously seen what a power of combustion is possessed by the
potassium, or the zinc, or the iron-filings; but none of them shew such
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