AER 
in several ways : but the best methods are 
by applying acids to certain metals ; by ex- 
posing animal, vegetable, and some mineral 
substances, in a close vessel, to a strong fire ; 
or by transmitting the vapour of certain 
fluids through red-hot tubes. In the first of 
these methods, iron, zinc, and sulphuric acid 
are the materials most commonly used. The 
acid must be diluted with five or six parts 
of water. Iron may be expected to yield 
in the common way about 1700 times its 
own bulk of gas ; or 41 ounces of iron, the 
like weight of sulphuric acid, and gw ounces 
of water, will produce one cubic foot of hy- 
drogen gas; <5 ounces of zinc, an equal 
weight of acid, and 30 ounces of water, are 
necessary for producing the same quantity. 
It is more proper to use the turnings or 
clappings of great pieces of iron, as of can- 
non, &c. than the filings of that metal, be- 
cause the heat attending the effervescence 
will be diminished, and the diluted acid will 
pass more readily through the interstices of 
the turnings, when they are heaped together, 
than through the filings, which stick closer to 
one another. The weight of the hydrogen 
gas thus obtained by means of sulphuric acid, 
is, in the common way of procuring it, gene- 
rally one-seventh part of the weight of com- 
mon air; and with the necessary precau- 
tions for- philosophical experiments, less than 
one-tenth of the weight of common air. We 
shall conclude this article with a description 
of some figures explanatory of the subject. 
Figure 1 (plate Aerostation) represents a 
balloon, DF, suspended by means of the 
poles G and II, and the cord, for the pur- 
pose of being filled with gas. It is kept steady 
and held down whilst filling by ropes, which 
are readily disengaged. A, A, are two tubs, 
about three feet in diameter, and two feet 
deep, inverted in larger tubs, B, B, full of 
water. At the bottom of each of the in- 
verted tubs there is a hole, to which is in- 
serted a tin tube ; to these the silken tubes 
of the balloon are tied. Each of the tubs, 
B, is surrounded by several strong casks, so 
regulated in number and capacity, as to be 
less than half full when the materials are 
equally distributed. In the top of these 
casks are two holes; to one of which is 
adapted a tin tube, formed so as to pass 
over the edge of the tub B, and through the 
water, and to terminate with its aperture 
under the inverted tub A. The other hole, 
which serves for supplying the cask with 
materials, is stopped with a wooden plug. 
When the balloon is to be filled, the com- 
mon air is first to be expelled, then the 
.ESC 
silken tubes are fastened round the tin one3 . 
the iron filings are to be put into the casks, 
then the water, and lastly the sulphuric 
acid. The balloon will speedily be inflat- 
ed by the gas, and support itself without 
the aid of the rope GH. As the filling ad- 
vances, a net is adjusted about it, the cords 
proceeding from the net are fastened to the 
hoop MN ; the boat IK is suspended from 
the hoop, and whatever is wanted for the 
voyage is deposited in the boat. When the 
balloon is sufficiently full, the silken tnbes 
are separated from the tin tubes, their ex- 
tremities are tied, and they are placed in 
the boat. When the aeronauts are seated 
in the boat, the ropes that held the balloon 
down are slipped off, and the machine as- 
cends in the air as in figure 2. In figure 3, 
is a representation of a part of Mr. Garnerin’s 
balloon in its ascent, to which is attached 
the parachute in its contracted state, and 
below is the car. Figure 4 shews the man- 
ner in which Mr. Garncrin descended in the 
car by means of the expanded parachute, 
after be had detached it from the balloon. 
In figure 5 is represented an apparatus, as 
described by Mr. Cavallo, for filling balloons 
of the size of two or three feet in diameter 
with hydrogen gas, after passing it through 
water. A is a bottle with the ingredients ; 
BCD a tube fastened in the neck at B, and 
passing through C, the cork of the other 
bottle, in which there is a hole made to re- 
ceive the tube, and to this the balloon is 
tied. Thus the hydrogen gas, coming out 
of the tube 1>, will pass first through the 
water of the bottle E, and then into the bal- 
loon. Two small casks may be used instead 
of the bottles A and E. 
/ERVA, in botany, a genus of the Mona- 
delphia Decandria class and order. The 
flowers are polyganous ; the calyx five-leaved 
and patent: the stamina are five; the pistil- 
lum is a globulous ovary, having a filiform 
style, terminated by a bifid stigma : the fruit 
is an oblong, single-seeded capsule, encom- 
passed by a calyx : there is but one species, 
viz. the M; aegyptiaca, or tomentosa, which 
grows on the sandy calcareous soil of Arabia. 
iESCHYNOMENE, a word from the 
Greek, signifying to be ashamed, because it 
retreats from the touch: bastard sensitive 
plant, in botany, a genus of the Diadelphia 
Decandria class and order, and of the natural 
order of Papilio Naceae, of which there are 
12 species found native in the East Indies, 
and cultivated in other hot countries. One 
of the species may be treated as hemp, and 
is used for the same purposes. 
