A E R 



AE R 



of pit-coal, expoftd to a red heat, yitlds about three ciiWc 

 feet of inflan^niable air, which, whether it be pafled throiigli 

 water or not, weighs about one-fourih of the weight of an 

 equal bulk of common air. 



Dr. Pricftley obfervcs, that animal or vegetable fubftanccs 

 will yield fix and even ten times more inflammable air, when 

 the tire is ludJenly increafed than when it is gently raifed, 

 though it be afterwards made veiy ilrong. And Mr. Ca- 

 vallo informs us, that the various fubflanees above enume- 

 rated generally yield all their inflammable air in about an 

 hour's time. Tiie ufual method is to indole the fubdances 

 in earthen or iron veflels, and thus to expofe them to a 

 llrong fire fufScicnt to make the vefTels red-hot ; the inflam- 

 mable air proceeding from the apertme of the vcflel, is re- 

 ceived into a tube or refrigeratoi^, and pallliig through the 

 tube or worm, is at lail cuUedled in a balloon or other vef- 

 fel. A gun-barrel has been often ufed for eflays of this 

 kind. The manner of conducing this procefs is particu- 

 larly deicribed by Mr. Cavallo, ubi infra. 



The lall method of obtaining iiiflammible air was lately 

 dilcovered by Mr. Lavoilier, and eJfo by Dr. Prleftley. 

 Mr. Lavoifier made the fteam of boiling water pafs through 

 the barrel of a gun, kept red-hot by burning coals. Dr. 

 Prieltley ufes, inftead of the gun-barrel, a tube of red-hot 

 brafs, upon which the fteam of water has no effeft, and 

 which he tills with the pieces of iron which are feparated in 

 the boring of cannon. By this method he obtains an in- 

 flammable air, the fpecitic gravity of whicli is to that of 

 common air as l to 13. In this method, 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 clofe 

 boiler is luted to one of its ends, and the worm of a refrige- 

 ratory is adapted to its other extremity. The middle part 

 of the tube is then funounded with burning coals, fo as to 

 keep about one foot in lengtii of it red-hot, and a fire is 

 always made under the retort or boiler fufficientto 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 aftion of vitriolic acid. 

 See Hydrogen. 



Balloons of the fmaller fize, fucli as thofu of two or three 

 feet in diameter, and alio bladders, may be filled with in- 

 flammable air, after pafling it through water, by means of 

 the following fimple apparatus. See Plate I. Pmiimat'ics, 

 fig. 3. A is the botde that contains the ingredients which 

 produce the gas : BCD is a tube in form of a fyphon, 

 faftened by one extremity into the neck of this bottle, and 

 paifing through a hole of the ftopper of another bottle E, 

 it extends fo far as almoil to touch the bottom of this bottle, 

 which is nearly full of water. To another hole made in the 

 cork of the bottle E is adapted another tube, to the out- 

 ward extremity of which a bladder, or the aperture of the 

 balloon is tied. The inflammable air, coming out of the aper- 

 ture D of the tube, paffes through the water of the bottle E, 

 and then enters into the bladder or balloon. Two fmall 

 caflis might be ufed inilead of the bottles A and E. 



Auetiier apparatus for producing hydrogen and conveying 

 it into a balloon is exhibited in ;?o-. 4. ABC is a veflel 

 made of clay, or of iron, in the form of a Florence flaflc ; 

 and the fubltance yielding gas is introduced into it fo as to 

 occupy about -}ths, or lefs, of its cavity. If the fubftance 

 fw;!! much by the Jittiou of the fire applied to it, a tube of 

 braf i, or riril a braf^ and then a leaden tube muft be luted to 

 the neck C of the veflel, and the extremity D of the tube is 

 Tnade to pais through the water of a tub H I, and to ter- 

 minate under an inverted veflel E Fj to the upper aperture 



of wliicli the balloon, or a tube going t« the balloon is 

 adapted. When the part, A B, of the veflel is put into 

 the tire, and made red-liot, the inflammable air that is gene- 

 rated will come out of the tube C D, and palling tlirough 

 the water of the tub, it will at lall enter into the balloon Ci. 

 As a confiderable quantity of common air remains in tlie 

 inverted veflel E F, before the operation is begun, it fliould 

 have a llop-cock, K, through which it may be drawn out 

 by fuftion, and then tlie water will afcend as high as the 

 llop-cock. The aperture of the vefll-I, E F, fliould be at 

 lead one foot below the furface of the water in HI; and 

 the fire fliould be at a fuflicient dillance from the tub H I, 

 that the inflammable air, if any of it fliould efcape, may 

 not take fire and do injury. 



The method of filling large aerollatic machines with rarc- 

 fi :d air is as follows. A fcaifold A B C D j' J'/alf 1 1 . /-. 5 . ) 

 the breadth of which is at leall two-thirds of the diameter of 

 the machine, is elevated about fix or eight feet above the 

 ground. From the middle of it defcends a well E F, 

 rifing about two or three feet above it, and reaching to the 

 ground, furniflied with a door or two, through which the 

 fire in the well is fupplied with fi:el. The well Ihould be 

 conftrufted of brick or of plallered wood ; and its diame- 

 ter fliould be fomewhat lefs than that of the machine. On 

 each fide of the fcaffold are erefted two malls H I, K L, 

 each of wliich has a pulley at the top, and rendered firm 

 by means of n.pes K G, K P, H P, H G. The machine 

 to be filled is placed on the fcaffold, with its neck vwind the 

 aperture of the well. The rope paffing over the pullies of 

 the two malls, ferves, by pulling its two ends, to lift the 

 balloon about fifteen feet or more above the fcaffold : and 

 the rell of the machine is reprefented by the dotted lines in 

 the figure M N O. The machine is kept Heady and held 

 down, whilil filling, by ropes paffing through loops or holes 

 about its equator; and thel'e ropes maybe eafily difengaged 

 from the machine, by flipping them through the loops, 

 when it is able to fuflain itfelf. The proper combufl:ibles 

 to be lighted in the well are thofe which burn quick and 

 clear, rather thafi fuch as produce much fmoke ; becaufe it 

 is hot air, and not fmoke, that is required to be introduei.d 

 into the machine. Small wood and llraw have been found 

 to be very fit for this purpofe. Mr. Cavallo obferves, as 

 the i-efult of many experiments with fmall machines, that 

 fpirits of wine are upon the whole the bell combullible ; 

 but its price may prevent its being ufed for large ma- 

 chines. As the current of hot air afcends, the machine 

 will foon dilate, and lift itfelf above the fcafi'old and gal- 

 leij, which was covered by it. The paflengers, fuel, in- 

 ftruments, &c. are_then placed in the gallery. When the 

 machine makes efforts to afcend, its aperture raufl be 

 brought, by means of the ropes annexed to it, towards the 

 fide of the well, a little above the fcafiold. The fire-place 

 is then fufpended in it ; the fire lighted in the grate ; and 

 the lateral ropes being flipped off, the machine is abandoned 

 to the air. It will appear in the atmofphere as it is repre- 

 fented in^'. 6. It has been determined by accurate expe- 

 riments, that only one-third of the common air dan be 

 expelled from thefe large machines ; and therefore, the 

 afcendlng power of the rarefied air in them can be efiimated 

 as only equal to half an ounce avoirdupois for every cub.c 

 foot. The apparatus for filling an inflammable air balloon 

 is reprefented in Jjg. 7. A, A are two tubs, about three 

 feet in diameter, and nearly two feet deep, inverted in 

 larger tubs, B, B, full of water. At the bottom of each 

 of the inverted tubs there is a hole, to which is adapted a 

 tin tube E, about feven inches in diameter, an.! fevcn or 

 eight inches long. To thefe tubes the filken tubes of the 



balloon 



