32 On Aérial Navigation. 
chief obstacle to their introduction. This causes the expense 
attending their structure and inflation, their tremendous power 
if assailed by winds, and the difficulty of disposing of them when 
not employed. The expense of structure would at present be 
about 300/. per ton; but if these vessels became of general utility; 
a much cheaper means of structure would probably soon be 
found out. The expense of inflating them with hydrogen gas is 
heavy by the present process; but as water consists of rather 
more than a sixth part of its weight of pure hydrogen * ; and as 
every portion of hydrogen according to its purity gives from 
ten to twelve times its own weight of support in a balloon, it 
follows that every ton of water that is decomposed for this pur- 
pose, will suspend very nearly two tons of burthen in the air, 
If this process, as I before suggested, be performed by exposing 
red hot iron to the action of steam, it appears, from the known 
proportion of oxygen in the black oxide thus formed+, that it 
will take about a ton and a half of iron to each ton of supporting 
power ; and hence an oven of three and a half yards cubed will 
contain sufficient iron drops or borings, allowing one half of the 
space for the free passage of the steam amongst them, to inflate 
the balloon I have described of fifty tons power. As the oxide 
will be reduced by melting the iron again in the ordinary way, 
no metal would be lost; and the process would not be expensive 
if conducted where coal and iron ore are found together, as is 
frequently the case in this kingdom. 
Charcoal will decompose water more rapidly and at a cheaper 
rate; and although the carburetted hydrogen thus obtained is 
generally much too heavy for inflating balloons ; yet as the com- 
pound nature of this gas seems to vary according to the quantity 
and circumstances under which the steam comes in contact with 
the ignited charcoal; and as Lavoisier and Meusnier obtained 
it at the specific gravity of 0-279, air being ‘1000, or rather 
more than three and a half times lighter than air, it is very pro- 
bable that some ready mode may be found of obtaining pure hy- 
drogen by the simple action of combustibles upon steam, which 
will render the floatage of balloons cheap enough for that or- 
dinary use which, sooner or later, this principle was designed to 
be of to mankind. Had hydrogen been a scanty substance, to 
be found with difficulty, its remarkable levity, though attractive 
as a matter of curious chemical research, would only have been 
tantalizing, as exhibiting a means of suspending heavy bories in 
* 85 Oxygen. + 27 Oxygen. 
15 Hydrogen. 73 Iron. 
100 Water. - 100 Black oxide. 
