On the Supply and Application of the Blow -pipe. aj^ 



making their valves air-tight, upwards of nine-tenths of the 

 air drawn into them efcnpes at other places than the proper 

 aperture. A pair of bellows of this kind, belonging to an 

 arlift of this citv, which were confidered as unLifuallv air- 

 tight, were found to difcharge the complement of their upper 

 compartment in fix-fourths of a minute, when the orifice of 

 the pipe was open; and in feven-fourths of a minute when 

 it was clofed. Hence it appears, that fix-fevenths of the air 

 injefted into the upper compartment efcaped at other places 

 than the proper aperture ; and if to this lofs were added that 

 fuftained by the lower compartment, the wafte would be 

 found much greater. As iu operating with thefe machines, 

 it is neceffary conftantly to move the foot, the operator can- 

 not leave his feat ; and, in nice operations, the motion of his 

 body is an inconvenience, if not a fource of failure. Bellows 

 of this kind cannot be ufed for fupplying combuftion with, 

 oxygen gas; becaufe, as this air is only to be obtained by a 

 chemical procefs, the fmalleft wa(te of it is of ferious con- 

 fequence; and as there is always a portion of air remaining- 

 in them, even when the boards are prcfled as near to each 

 other as the folding of the leather will permit, any fmall quan- 

 tity of oxygen gas which might be drawn into them would 

 be thereby contaminated. 



It feems that the only inftrument hitherto ufed for the 

 fupply of combuftion with oxygen gas, is the gafometer of 

 the celebrated Lavoifier: but this machine, although admi- 

 rably calculated for the purpofes of that great philofopher, is 

 too unwiekiy atid expcnfive for ordinary ufes. 



Being i'enfible of the advantage which would refult from 

 the invention of a more perfcci; method of fupplying the blow- 

 pipe with pure or atmolpheric air, I was induced to fearch 

 for means of accomplKhing this objeft. Having obferved 

 the cheapnefs, (Irength, and tight ncfs, of coopers' veflels, I 

 became dclirons of forming an apparatus for my purpofe, bv 

 means of hydroltatic prclliire exerted within them. I foon 

 found that this could not be efVec-ted conveniently without 

 the ufe of leather. Obliged to relbrt for afiiftance to' this ma- 

 terial, I endeavoured to apply it in fiich manner, as to remedy 

 the evils refulting from the ufc of it in the common kinds of 

 bellows. The cauies of thefe evils appeared to bo, the open- 

 ing of the pores and joints of thefe in(irumeiits by drynefs, 

 and the teiifion lowhrch they are fo frequently fubjecied. I 

 therefore determined to lubiK'-t the lenlhcr which I fliould 

 uf-, to moifture and coi^preiHon. In this I fucceedcd, and 

 derived the cxptck-d advuaiugc. frouj fucucfs. The refult of 



- my 



