174 ' A E R O S T 
jerminate under a fort of inverted veflel, to the upper 
<iperture of which the balloon is adapted. Things thus 
prepared, if the lower part of the veflel be put into the 
4 ire, and made red-hot, the inflammable air produced 
will come out of the tube, and, pafling through the wa¬ 
iter, will at laft enter into the balloon. Previous to the 
operation, as a confiderable quantity of common air re¬ 
mains in the inverted veflel, which it is more proper to 
expel, the veflel (hould have a flop-cock, through which 
the common air may be flicked out, and the water afeend 
as high as the flop-cock. Care muft be taken that the fire 
ufed in this procefs be at a fufficient diflance, othenvife 
it may happen to fire the inflammable air. 
Another method of obtaining inflammable air was late¬ 
ly difeovered by M. Lavoilier, and alfo by Dr. Priefiley. 
M. Lavoilier made the fleam of boiling water pafs through 
the barrel of a gun, kept yed-hot by burning coals. Dr. 
Priefiley ufes, .inftead of the gun-barrel, a tube of red- 
hot brafs, upon which the fleam of water has no effect, 
and which he fills with the pieces of iron which are fepa- 
rated in the boring of cannon. By this method he ob¬ 
tains an inflammable air, the fpecific gravity ot which is 
to that of common air as one to thirteen. In this method, 
not yet indeed reduced to general practice, a tube about 
three-quarters of an inch in diameter, and about three 
feet long, .is filled with iron-turnings; then the neck of a 
retort, or dole boiler, is luted to one of its ends, and the 
worm of a refrigeratory is adapted to its other extremity. 
The middle part of the tube is then furrounded with burn¬ 
ing coals, fo as to keep about one foot in length of it red- 
hot, and a fire is always made under the retort or boiler 
fufficient to make the water boil with vehemence. In this 
procefs a confiderable quantity of inflammable air comes 
out of the worm of the refrigeratory. It is faid that iron 
yields one half more air by this means than by the action 
of vitriolic acid. 
For filling large balloons, a greater apparatus is necef- 
fary; and tlie only materials that can, with any certainty 
of fuccefs, be employed for producing the proper gas, 
are, oil of vitriol, and iron filings or turnings. 
It has indeed been recommended to ufe zinc inftead of 
iron-filings, becaufe white vitriol, the fait produced by 
the union of tire vitriolic acid and zinc, is much more va¬ 
luable than the green fort produced by the union ot the 
fame acid with iron. But though this is undoubtedly the 
cafe, it will as certainly be found, upon trial, that the fu- 
perior price of the zinc will be more than an equivalent 
for all the advantage that can be derived from the addi¬ 
tional price of the white vitriol. For a balloon of thirty 
feet diameter, Mr. Cavallo recommends 3900 pounds of 
iron-turnings, as much oil of vitriol, and 19,500pounds 
of water. Thefe proportions, however, appear too great 
with refpeft to the acid and metal, and too little with re- 
JpetSf to the water. Oil of vitriol will not exert its power 
upon iron unlefs it be diluted with five or fix times its 
quantity of water; in which cafe, a much fmaller quan¬ 
tity of both acid and metal will ferve. M. Lunardi, who 
from the number of his voyages had certainly much prac¬ 
tical knowledge in aeroftation, filled his balloon with about 
aooo pounas_of iron, as much vitriolic acid, and 12,000 
f iounds of water. The iron was placed in his vefiels in 
ayers, with ftraw between them, in order to increafe the 
furface. His apparatus was not materially different from 
that of Mr. Cavallo, and is reprefented in the plate, where 
there are two tubs, about three feet in diameter and near¬ 
ly two feet deep, inverted in large tubs filled with water. 
In the bottom of each of the inverted tubs a hole is made, 
and a tube of tin adapted, which is about feven inches in 
diameter, and feven or eight long. To thefe tubes the 
(liken ones of the balloon are tied. Round each of the 
tubs, five, fix, or more, ftrong cafks are placed ; in the 
top of each two holes are made, and to one of thefe holes 
a tin tube is adapted, and fo ftiaped, that, pafling through 
the water, it may terminate with its aperture under the 
inverted tub. The other hole of thefe cafks ferves for 
A T I O N. . 
the introduction of materials, and is flopped with a wood¬ 
en plug, When the balloon is to be filled, put the-net 
over it, and let it be fufpended in the centre ; and, having- 
expelled all the common air from it, let the filken tubes 
be faftened round the tin ones, and, the materials being 
put into the cafks, the inflammable air, pafling into the 
balloon, will,foon diftend, and render it capable of fup- 
porting itfelf; after which the rope may be flipped off. 
As the balloon continues to be filled, the net is adjufted 
properly round it, and the boat, being placed between the 
two lets of calks, is faftened to the hoop, with every thing 
elfe that is required to be fen't up, as ballad, inflniments, 
&c. At laft, when the balloon is little more than three- 
quarters full, the filken tubes are feparated from the tin 
ones of the inverted tubs, and, their extremities being 
tied up, are placed in the boat. Laftly, the aeronauts 
being feated in the boat, the lateral ropes are flipped off, 
and the machine is abandoned to the air. This apparatus 
was at laft reduced by M. Lunardi to its utmoft fimplicity, 
by ufing only two large cafks, and fuffering the vapour to 
go into thebatloon without pafling through water. Thus, 
his balloon w as filled in lefs than half an hour, when, by 
the former method, it had required two hours at lead:. 
The finking of his caffs in the ground was alfb an addi¬ 
tional convenience, as it created no confulion, and ren¬ 
dered the materials much more eafily conveyed into them. 
With regard to the rarefied-air balloons, tire method of 
filling them is as foilows:—A fcaffold, the breadth of 
which is at leaf! two-thirds of the diameter of the ma¬ 
chine, is elevated about fix or eight feet above the ground'.. 
From the middle of it defeends a well, riling about two or 
three feet above it, and reaching to the ground, furnifned 
with a door or two, through which the fire in the well is 
fupplied with fuel. The well fliould be conftriufted of 
brick or of plaftered wood, and its diameter fliould be 
fomewhat lefs than that of the machine. On each fide of 
the fcaffold are eretied two mails, each of which has a pul¬ 
ley at the top, and rendered firm by means of ropes. The 
machine to be filled is to he placed on the fcaffold, with its 
neck round the aperture of the well. The rope, pafling 
over the pulleys of the two mails, ferves, by pulling its two 
ends, to lift the balloon about fifteen feet or more above 
the fcaffold. The machine is kept fteady, and held down, 
whilft filling, by ropes palling through loops or holes 
about its equator;, and thefe ropes may eafily be difenga- 
ged from the machine, by flipping them through the loops 
when it is able to fuftain itfelf. The proper combuftibles 
to be lighted in the well, are thofe which burn quick and 
clear, 'rather than Inch as produce much fmoke; becaufe 
it is hot air, and not fmoke, that is required to be intro¬ 
duced into the machine. Small wood and draw have been 
found to be very fit for this purpofe. Mr. Cavallo ob- 
ferves, as the refult of many experiments with fmall ma¬ 
chines, that fpirits of wine are upon the whole the belli 
combuftible; but its price may prevent its being ufed for 
large machines. As the current of hot air afeends, the 
machine will foon dilate, and lift itfelf above the-fcaffold 
and gallery which was covered by it. The paffengers, 
fuel, inftruments, &c. are then placed in the gallery. 
When the -machine makes efforts to afeend, its aperture 
muft be brought, by means of the ropes annexed to it* 
towards the lide of the well a little above the fcaffold 3 
tire fire-place is then fufpended in it, the fire lighted in 
the grate, and, the lateral ropes being flipped off, the ma¬ 
chine is abandoned to the air. It has been determined by 
accurate experiments, that only one-third of the common 
air can be expelled from thefe large machines; and there¬ 
fore the afeending power of the rarefied air in them can 
be eftimated as only equal to half an ounce averdupoile 
for every cubic foot. 
The conduct of balloons, when conftrufted, filled, and 
actually afeending in the atmofphere, is an object of great 
importance in the practice of aeroftation. The method 
generally ufed for elevating or lowering the balloons with 
rarefied air, has been the increafe or diminution of the 
fire; 
