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XCIIl. On Safety-lamps, and the Barrier formed ly Wire- 

 gauze against the Passage of Flame. By J. Murray, Esq, 



To Mr. Tilluch. 



Sir, — Jylu. Langmire, in the last number of The Annals of 

 Philosophy, pronounces tiie limit 1 have assigned to the barrier 

 against flaiiie — to be inconsistent with the deductions of Sir 

 H. Davy. By a reference to my paper Mr. L. will find that 

 this had a relation to simple unexplosive flame, and was intro- 

 duced as explanatory of the chasm obtaining between flame 

 and metallic surfaces ;- and if this gentleman will have the good- 

 i>ess to place a series of wires on a frame, these wires being one- 

 eighth of an inch apart, he will find (as I did) that such an ar- 

 rangement is effectual iu cutting off the comniunication of flame. 

 If he will pleast! to be referred to the Rev. Mr. Hodson's Narrative 

 iu your last number, page 351, he will also discover that Sir H. 

 expressly names one-eighth ; this I hail as corroborating my 

 inference, and value it the more as it has been for the first time 

 to me published. — The safety-lamps are constructed of wire- 

 gauze having 7^-1 apertures in the square inch; and I repeat, 

 that I do not consider any danger is to be ajipreliended, if by 

 accident the alternate mesh be broken down ; for even then, the 

 intervals would be only distanced one fourteenth of an inch. 



The double cylinder is by no means necessarv, and may be in- 

 jurious where the exterior one is of copper, for the following 

 reasons : 



1. It is violently acted upon by fire-damp. 



2. Dissimilar metals being employed, a Galvajiic action may 

 be induced, and corrosion take place. And, 



3. The sebacic acid df lancid oil acts forcibly on copper. 



I will go further than even JSir 11. Davy has done, and assert, 

 that, even should an explosion occur within the lamp (the gauze 

 being formed of loose pliant materials), and the im)jerfectly con- 

 structed cylinder burst, by means of it; even then, no danger 

 would accrue to the minerr», for the extinction would instantly 

 succeed the explosion, when confined within the cylinder. In 

 one of the collieries wlilcli 1 descended, the under-viewers using 

 a lamp procured from Newcastle, niade of fine brass wire as soft 

 and pliant almost as common thin writing-paper, the cylinder 

 loosely connected with the socket, about' the screw, and the 

 seam indilTercntly joined ; — this impj-oper instrument, having 

 nothing to recommend it but a rude imitation of that most valu- 

 able machine, T/Mw/ in kis hands at the joitiing of the seam ; yet 

 I^e was perfectly secure, and escaped without the least injury. 

 Ff2 The 



