ZZ On ibe prtfent State of Aerojlation. 



To provide againfl; thefe two circumftances, the aeronaut 

 ought not to omit fuhjecling the iron turnings to the aftion 

 of a ftrong fire amidfl: carbonaceous matters, for at leaft an 

 hour, a day or two before his propofed ufeefthem. The 

 thicknefs of the iron nnift be alfo noticed, as, under the mofi: 

 favourable circumftances, the acid never penetrates it more 

 than half an inch: therefore all the weight of iron that re- 

 mains over and above a furface of half an inch depth every 

 way, becomes ufelefs; the coat of newly formed oxide of iron 

 efTeftually guarding the remaining metal from folution : for 

 want of attending to this circumflance, the quantity of metal 

 has frequently proved deficient to the end propofed, to the 

 great difappointment of the experimenter. 



Alfo where the public have to rely on tVie good faith of the 

 exhibiter, he ought to try the ftrength of his acid previous to 

 employing it; and this, not by the ordinary methods of fpe- 

 cific gravity, nor the quantity of alkali it will faturate*, but 

 by the a6lual procefs, in the fmall way, of what he propofes 

 to perform on the day of afcent : by thefe means he cannot 

 fail of fucceeding. 



But the above is not the onlv method of procuring inflam- 

 mable airf: the pafling of water over red-hot metals is fol- 



tiite the entrance of the inflammable air into the balloon, the varniftied 

 liiken tube, proceeding from the inverted funnel, niuft rather afcend than 

 otherwife in its courfe to the balloon, Vvhich may be esfily managed by 

 iupporting it along a ladder having a gentle inclination upwards, I appre- 

 hend the coft of the larger tubs of looo gallons each will be lefs expenfivc 

 than to have rccourfe to twenty or thirty butts for the purpofc; which, by 

 dividing the procefs, caufes greater apprchenfions for failure with refpett 

 TO the lightnefs of fo many vcITcIs and tubes; befidcs the inconvenience of 

 having to procure fo great a number of c fks for every frefli vovngc, when 

 undertaken as a public exhibition in plnces far diftant from each other. 



The I'ulphate of iron, the pgoduft of the mutual aflion of the acid and 

 iron, is a fubftance much ufed in the arts under the name of green cop- 

 peras : the chemift, dver, calico-printer, ink-maker, refiner, &:c. have great 

 demand for this article. It may therefore be either dil'pofcd of , or diftilled 

 per f- to regain the acid ; while the rcfiduum, by a fuithercaicination, may 

 be converted into that fpccies of oxide known bv the name of colcothar, 

 an article mucii employed for pollfliing glafs and metals, and alfo as a 

 pigment. 



' We arc liable to miftakes if we rely on the fpecific gravity of the acid 

 (ufiialiy varying from i'6 to I'S), which is augmented by its containing 

 in folution neutral frilts, efpecially fulphate of potafti ; an adulteration not 

 unfrequently practifed. The quantity uf alkali required to faturate a eiven 

 quantity of an acid, can never deteft the abfolute quantity of the indivi- 

 dual acid we are u\ fearch of, but only indicate the degree of acidity of the 

 %vlio!e, without any regard to the fpecific radicals. 



\ Inflammable air is procured in many chemical operations; but it is 

 ufelefs to mention heie any other than fuch as arc advantvigeoufly appli- 

 cable to actoftatic purpofes. 



lowed 



