A E R O S T 
'fhe bed: method of cutting the pieces of filk that are 
to form a balloon, is to defcribe a pattern of wood pr ftifF 
card-paper, and then to cut the (ilk upon it. In cutting 
the pieces after fuch pattern, care Ihould be taken to 
leave tliem about three-quarters of an inch all round lar¬ 
ger than the pattern, which will be taken up by the feams 
in joining. 
To the upper part of the balloon there fhould be adapt¬ 
ed, and well fitted in, a valve opening inwards; to w hich 
Ihould be fattened a firing palling through a hole made in 
a fmall piece of round wood fixed in the low'd! part of 
the balloon oppofite to the valve, the end of this firing 
fattened in the car below, fo that the aeronaut may open 
the valve when occation requires. The aftion of this 
valve is effedted by a round brafs plate, having a round 
hole about two or three inches diameter, covered on both 
fides with ftrong fmooth leather. On the infide there is a 
(butter of brafs, covered with leather, which ferves to 
clofe the hole, being about two inches larger in diameter 
than the hole. It is fattened to the leather of the plate, 
and by a fpring, which need not be very firong, it is kept 
again!! the hole. The elafticity of the gas.itfelf will help 
to keep it (hut. To this flnitter the firing is fattened, by 
which it is occafionally opened for the efcape of the gas. 
A fmall firing or other fecurity Ihould be fixed to the 
flnitter and the plate, fo as not to admit the flnitter to be 
opened beyond a certain fafe difiance. To the lower part 
of the balloon two pipes fhould be fixed, made of the fame 
fluff as the envelope ; fix inches diameter for a balloon of 
thirty feet, and proportionabiy larger for balloons of a 
greater capacity. They muft be long enough, for the car. 
For balloons of eighteen feet and.lefs diameter, one neck 
or pipe will be fufficient. Thefe pipes are the apertures 
through which the inflammable gas is introduced into the 
balloon. 
The car or boat is befi made of wicker-work, covered 
with leather, and well painted or varnifhed over; and the 
proper .method of fufpending it, is by ropes proceeding 
from the net which goes over the balloon. This net 
Ihould be formed to the Ihape of the balloon, and fall 
down to the middle of it, with various cords proceeding 
from it to the circumference of a circle about two feet be¬ 
low the balloon; and from that circle other ropes Ihould 
go to the edge of the boat. This circle may be made of 
wood, or of leveral pieces of (lender cane bound together. 
The melhes of the net may be fmall at top, againft which 
part of the balloon the inflammable air exerts the greateft 
force; and increafe in fize as they recede from the top. 
A hoop has fometimes been applied round the middle of 
the balloon to fallen the net. This, though not abfolute- 
ly neceflary, is befi made of pieces of cane bound toge¬ 
ther, and covered with leather. 
With regard to the rarefied-air machines, Mr. Cavallo 
recommends firft to foak the cloth in a folution of fal am¬ 
moniac and common fize, ufing one pound of each to eve- 
jy gallon of water; and, when the clotii is quite dry, to 
paint it over in the infide with feme earthy colour, and 
firong fize or glue. When this paint has dried perfectly, 
it will then be proper to varnilh it with oily varnilh, which 
might dry before it could penetrate quite through the 
cloth. Simple drying linfeed oil will anfwer the purpofe 
as well as any, provided it be not very fluid. 
It now only remains to give fome account of the me¬ 
thod by which aeroftatic machines may be filled with 
their proper gas, in order to give them their power of af- 
cending into the atmofphere; and here we are enabled to 
determine with much greater precifion concerning the in¬ 
flammable air-balloons than the others. With regard to 
them, a primary confideration is, the mod proper method 
of procuring the inflammable air. It may be obtained in 
various ways, as has been fhewn under the article Aero¬ 
logy. But the moft advantageous methods are, by ap¬ 
plying acids to certain metals; by exppfinganimal, vege¬ 
table, and fome mineral, fubftances, in a clofe veil’d to a 
Vol. I. No, ii. 
A T I O N. i 7 j 
firong fire; or by tranfmitting the Vapour of certain flu¬ 
ids through red-hot tubes. 
In the firfi of thefe methods, iron, zinc, and vitriolic 
acid, are the materials moft generally tifed. The vitrio¬ 
lic acid muft be diluted by five or fix parts of water. Iron 
may be expefited to yield in the common way 1700 .times 
its own bulk of gas; or one cubic foot of inflammable 
air to be produced by four ounces and a half of iron, the 
like weight of oil of vitriol, and twenty-two ounces and 
a half of water. Six ounces of zinc, an equal weight of 
oil of vitriol, and thirty ounces of water, are neceflary 
for producing the fame quantity of gas. It is more pro¬ 
per to life the turnings or chippings of great pieces of 
iron, as of cannon, &c. than the filings of that metal, be- 
caufe the heat attending the eftervelcerrce will be dimi- 
niftied; and tire diluted acid will pafs more readily thro’ 
the interftices of the turnings when they are heaped toge¬ 
ther, than through the tilings, which (tick clofer to one 
another. The weight of the inflammable air thus ob¬ 
tained by means of acid of vitriol, is, in the common way 
of ■procuring it, generally one-feventh part of the weight 
of common air; but, with the neceflary precautions for 
philofophical experiments, lefs than one-tenth of the 
weight of-common air. Two other forts of elaftic fluids 
are fometimes generated with the inflammable air. Thefe 
may be feparated from it by palling the inflammable air 
through water in which quick-litne has been dilfolved. 
The water will abforb thefe fluids, cool the inflammable 
air, and prevent its over-heating the balloon when intro¬ 
duced into it. 
Inflammable air may be obtained at a much cheaper 
rate by the action of firC/On various fubftances; but the 
gas which thefe yield is not fo light as that produced by 
the effervefcence of acids and metals. The fubftances 
proper to be ufed in this way are, pit-coal, afphaltuni, 
amber, rock-oil, and other minerals; wood, and efpecially 
oak, camphor-oil, fpirit of wine, ether, and animal fub- 
ftances, which yield air in different degrees, and of vari¬ 
ous fpecifi.c gravities; but pit-coal is the preferable fub- 
ftance. A pound of this expofed to a red heat yields 
about three cubic feet of inflammable air, which, whe¬ 
ther it be palfed through water or not, weighs about one- 
fourth of the weight of common air. Dr. Prieftley found 
that animal or vegetable fubftances will yield fix or (even 
times more inflammable air when the fire is fuddenly in- 
creafed than when it is gently raifed, though it be after¬ 
wards made very firong. Mr. Cavallo obferves, that the 
various fubftances above enumerated generally yield all 
their inflammable air in about one hour’s time. The ge¬ 
neral method is, to inclofe the fubftances in iron or earth¬ 
en veflcls, and thus expofe them to a ftrong fire fufficient 
to make the veflels red-hot: the inflammable air proceed¬ 
ing from the aperture of the veflel is received into a tube 
or refrigeratory, and, palling through the tube or w'orm, 
is at laft collected in a balloon or other veflel. A gun- 
barrel has often been ufed for eflays of this kind. The 
fubftance is put into it fo as to fill fix or eight inches of its 
lowed part, the remainder filled with dry land: a tube, 
adapted to the mouth of the barrel, is brought into a ba¬ 
ton of water under an inverted receiver; a.nd, the part of 
the harps! containing the fubftance being put into the fire 
and made red-hot, the inflammable air is collected in the 
inverted receiver. As the gun-barrel cannot ferve for 
producing'a large quantity of inflammube air, Mr. Ca¬ 
vallo recommends, as the moft advantageous Ihape, the 
following contrivance :—Let the veil'd be made ot clay, or 
rather of iron, in the ftiape of a Florence fialk, fome what 
larger, and whofe neck is longer and larger. Put the 
fubftance to be ufed into this veflel, fo as to fill about four- 
fifths or lefs of its cavity. If the fubftance is of fuch a 
nature as to (well much by the aCtion of the fire, lute a 
tube of brafs, or firft a brafs and then a leaden tube, to 
the heck of the veil'd; and let the end of the tube be 
rounded, fo that going into the water of a tub, it may 
Y y terminate 
