1+6 IvJlruSl'ions for Deeompofmg 



prodiiA of giz from the experiment would have been contaminated. Such curved er- 

 Iremiiics were however lefs convenient than-ilraight ones, on account of the greater diffi- 

 culty of transferring from the former than from the latter. See fig. i and 2, Plate XI. 



The diameter of tlie tubes fliould not be more tl)an i-8th or lefs than i-i ah of an inch. 

 At lealt in my experiments thefc tubes anfwercd bcit. If they were wider, the difcharge 

 rcquifite to produce gaz broke the tube. If the tubes be narrower than juft mentioned, the 

 experimenter will find it dilhcult and tedious to transfer the gaz, through the curved part, 

 into a refervoir, in thofe cafes in which a large rjuantity is wanted for examination. Where 

 however the objecl is merely to (hew the produdlion of gaz by means of the ele£lrica1 

 difcharge palTcd through water, between two wires ; and the inllant difappearance of gaz 

 fo produced by pairing through it an ele£lric fpark, the narrowetl tubes are moft eligible; 

 as with them the experiment can be made in a fliorter time. But there was one incon- 

 venience experienced from very narrow tubes, namely, the bubbles of gaz were very apt 

 to hang near the end of the upper wire inflead of afcending ; and they were apt to form 

 large bubbles, with water between each •, in which fituation the difcharge frequently 

 fraftuted the tube, or made gaz to difappear by combullion in the courfe of the experiment. 

 To poflefs at once the advantages of the narrow and wide tubes ; about three to fix 

 inches of narrow tube were joined by fufion to a bottom part of wider tube (fee Fig. 3)} 

 into the curve of which tube the gaz produced was let up from time to time ; fo that this part 

 frequently contained the produfls of ten or more experiments before the gaz was transferred 

 into the refervoir. The vaft number of tubes which were broken in this experiment induced 

 me to try various dilTerent kinds of them. I experienced no advantages from annealing 

 tubes ! but their being feemingly rendered more brittle, and harder, by this treatment, was an 

 ■effeft which I leaft of all expected. Tubes with thin fides anfwered jufl as well as with thick 

 ones. Bohemian green glafs tubes were found excellent for this experiment, as they were 

 much lefs apt to be cracked by the difcharges than any kind of Engiifli glafs. To fave time 

 and trouble in fo frequently letting out gaz produced in very narrow tubes, a fmall bulb was 

 made at the fealed end (fee Fig. 4 ). in this cafe, however, as the upper wire mud be 

 fhorter than other narrow tubes, it was more difficult to regulate the explofion. 



Althotigh common atmofpherical air is an eledlric, and water is a conductor of cleftricity, 

 it appears that the difcharge pafles with more refiflance from wire to wire through wSer in 

 the above experiment, than through common air under otherwife the fame circumftances. 

 The reafon of which is this: air being an elaftic and very rare fluid, it more readily gives 

 ■way to the electric difcharge than water ; and it can therefore pafs through a longer and 

 thicker column of air between two wires, without breaking the glafs tubes, than it can ' 

 through water. For although water is a conduftor, yet in a very fmall quantity it is a very 

 inditFetent one ; fo that its denfity and defect of elaflicity more than compenfate for its con- 

 du£ling power. Hence alfo, and on account of the conducing power of water, the reafon of 

 the upper wire in this experiment being (hortcr in proportion as the tube is wider; and on the 

 fame account will be feen the reafon of the advantages of a fmall upper wire over thicker ones. 



It will be necefiary 10 add, that the tubes with curved extremities can only be filled by 

 fitting them in water under a receiver, and exhaufling the air from the receiver, tubes, and 

 water; then, by letting in the air again, the water will be forced up into the tubes. Some- 

 times, however, I have filled the tubes by fetting them in P.ipin's digeftor. 



I Thefc 



