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balloon are tied. Eacli of the tubs, B, is fiiiroundcd by 

 fcvcral Ilrong caflc^, fo regulated in number ai;d capacity, 

 as to be lefs than half full, when the materials arc equally 

 dillributed. In the top of each of thefe c.ifks are two 

 holes ; and to one of the holes is adapted a tin tube, formed 

 fo as to pafs over the edge of the tub D, and through the 

 water, and to terminate with its aperture^under the inverted 

 tub A. The other hole, which fervcs for fupplying the 

 ca!l< with materials, is flopped with a wooden plug. Thefe 

 tin tubes may be about tliree inches and a half in diatpeter, 

 and the other holes may be fmaller. Two marts, with a 

 rope, &c. are uled for this machine, as well as for the for- 

 mer, although tliey are not abfolutely necelTary ; becaufe 

 the balloon, bv means of a nanow fcaffold, or other con- 

 trvance, mav be elevated five or fix feet above the level of 

 the tubs A A. When the balloon is to be filled, the net 

 is put over it and fufpended, as exhibited in CDF; and 

 having expelled all tiie common air from it, its filk tubes 

 are failened round the tin tubes E E, and the materials in 

 the caPivS are properly proportioned ; the iron being firil put 

 in, then the water, and lailly the vitriolic acid. The bal- 

 loon will foon be inflated by this inflammable air, and fup- 

 port itt-'lf without the aid of the rope G H. As the filling 

 advances, the net is adiuilcd round it, the cords, proceed- 

 ing from the net, are faftened to the hoop M N ; the boat 

 I K is fufpended from the hoop M N, and every tiling ne- 

 ceffary for the voyage is depofitcd in the boat. When the 

 balloon is a httle more than three quarters full, the filken 

 tubes are feparated from the tin tubes, and their extremities 

 being tied, they are placed in the boat. Finally, when 

 the aeronauts are feated in the boat, the lateral ropes are 

 flipped off, and the machine afcends in tlie air, appearing 

 as in _^. 8. In order to produce fuch a- bulk of in- 

 flammable air as is neceffar)' for a balloon of 30 feet in 

 diameter, whofe capacity is 141 37 cubic feet, there will be 

 required about 3900 pounds of iron turnings, 3900 pounds 

 of- v'itrioUc acid, and 19500 pounds of water. The balloon 

 will not be above three quarters full. 



Thefe proportions, ftated by Mr. Cavallo, are too great 

 with refpecl to the metal and acid, and too fmall with re- 

 gard to the water. Mr. Lunardi, who had confiderable 

 experience in the praftice of aeroftation, filled his balloons 

 at Edinburgh and Glafgow with about 7000 pounds of the 

 chippings of cannon procured fromCarron, the fame quantity 

 of vitriolic acid, and 12,000 pounds of water. The iron was 

 placed in layers in his velTels, with ftraw between them, in 

 order to enlarge the furface expofed to the aclion of the 

 acid. He ufed only two large calks, which were funk in 

 the ground, and conveyed the gas into the balloon without 

 paiTing through water ; and he contrived to fill his balloon 

 in lefs than half an hour, which operation had on former 

 occafions required at leaft two hours. 



The inflammable air with which they fill their balloons 

 at the Aeroftatic Inftitute, not long fince eftablifhed in 

 France, is obtained by the following method, which is 

 fimple and not very expenfive. Six cylinders, or tubes of 

 iron, are fixed by niafonry in a furnace of cafy and expe- 

 ditious conllruftion, in fuch a mariner that the two' ends of 

 each cylindL-r projeft out of the furnace ; and thefe are 

 fm-nifhcd with ftrong covers or lids of iron. Into thefe 

 cyhnders are introduced tubes of metal, one of which fcrves 

 to coiivej' warm water into the red-hot cylinder, and the 

 other to convey the air which is produced through a refer- 

 voir filled with ca iftic ley, into the balloon. The cylinders 

 are partly filled with the chippings or turnings of iron that 

 are procure,! from the boring of cannon. The exceffive heat 

 of the furnace, which is maintained by a fupply of char- 

 I 



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coal during the operation, is communicated to the cylinder* 

 and their contents. In this llate, billing water is conveyed 

 by one of the tabes to each cylinder ; and as foon .is it 

 communicates with the i:;flamed iron, the water is decom- 

 pofed : the one part, called the oxygen, attaches itfelf to 

 the iron at.d calcines it ; but the other part, or the hydro- 

 gen, is combined with a quantity of the igneous fubftan.ce, 

 called caloric, and becomes hydrogenous gas, or inflamma- 

 ble air, which remains in a permanent ilate of claftic 

 fluidity, and weiglfs feven or eight times lefs than the 

 atmoipheric air. As the water contains a fmall quantity of 

 carbon or fixed air, which would add weight to the air of 

 the balloon, it is made to pafs through water in which 

 caulHc alkali has been diflblved. This fluid attaches the 

 carbon to itfelf, and thus the pure inflammable air is con- 

 veyed into the bal'oon. The cylinders, in this operation, 

 are fometimes fufed ; for preventing which accident, a 

 pyrometer is annexed to the extremity of the cylinder which 

 projects from the furnace ; and the fire is regulated by a 

 fcale conncfted with the pyrometer. The operation of 

 filling a balloon, 30 feet in diameter, in this way wiD occupy 

 about four hours. 



In eftimating the afcending power of thefe machines, 

 that of the inflammable air Ihould be confidered as equal to 

 one ounce avoirdupois for every cubic foot, which is one 

 fixth of the weight of common air ; and therefore, if the 

 capacity of a balloon is 12000 cubic feet, and three-fourths 

 of it are filled with inflammable air, obtained from iron and 

 diluted vitriolic acid, the afcending power of that ga$ 

 may be eftimated at 9000 ounces, or 562^ pounds; from 

 which the weight of the covering, boat, and other ap- 

 pendages, mull be fubti-acled. 



The conducl of balloons, when confhructed, filled, and 

 adlually afcending in the atmofphere, is an obieft of great 

 importance in the praftice of aeroftation. The method 

 generally ufed for elevating or lowering the balloons with 

 rarefied air, has been the increafe or diminution of the fire ; 

 and this is entirely at the command of the aeronaut, as long 

 as he has any fuel in the gallen^. The inflammable air- 

 baUoons have been generally raifed or lowered by diminilhing 

 the weight in the boat, or by letting out fome of the gas 

 through the valve. But the alternate efcape of the air in 

 defcending, and difcharge of the ballad for afcending, will 

 by degrees render the machine incapable of floating ; for in 

 the air it is impoffible to fupply the lofs of ballaft, and very 

 difficult to fupply that of inflammable air. Thefe balloons 

 will alfo rife or fall by means of the rarefaftion or condenfa- 

 tion of the inclofed air, occafioned by heat and cold. It 

 has been propofed to aid a balloon in its alternate motion of 

 afcent and defcent, by annexing to it a veflel of common 

 air, which niight be condeufed by lowering the machine, 

 and rarefied again, by expelling part of it, for railing the 

 machine. But a vefiel adapted to this purpofe mud be very 

 ftrong, and, after all, the afliftance afforded by it would 

 not be very confiderable. M. Meunier, in order to attain 

 this end, propofes to inclofe oi\e balloon filled with common 

 air in another filled with inflammable air : as the bidloon 

 afcends, the inflammable air is dilated, and of courfe com- 

 preffes the internal balloon containing common air ; and by 

 diminilhing its quantity, leffens its weight. If it fliould be 

 ncccffary to fupply this lofs, he fays it may be eafily done 

 by a pair of bellows fixed in the galler)'. Others have pro- 

 pofed to annex a fmall machine with rarefied air to an in- 

 flammable air-balloon by ropes, at fuch a diftance that the 

 fire of the former might not affeft the inflammable air of 

 the latter : the whole apparatus, thus combined, of balloons 

 formed on the two principles of heated and inflammable air, 



might 



