WIRE-GAUZE SAFETV-LAMP. 



door in tlie fide, which is inftantly clofed, both lights will 

 burn for a few feconds, and be extinguifhed togeth'^r. 



A fimilar phenomenon occurs : if in a clofe lantern fup- 

 plied with a quantity of air merely fufficient to fupport a 

 certain flame, a mixture of fire-damp and air is gradually 

 admitted, the firft effeft of the iire-damp is to produce 

 a large flame round that of the lamp, and this flame con- 

 fuming the oxygen which ought to be fupplied to the 

 lamp, and the ilandard of the power of the air to fupport 

 flame being lowered by the admixture of fire-damp and by 

 its rarefa<9tion, both the flame of the fire-damp and that of 

 the lamp is extinguifhed together ; and as the air contained 

 a certain quantity of azote and carbonic acid before the ad- 

 miflion of the fire-damp, their effeft by mixing it is fuch 

 as to prevent an explofion in any part of the lantern. 



In an experiment which fir H. Davy made, to afcertain 

 , that the flame was extinguiflied in the lantern, though 

 , the mixture was ftill explofive which fupplied the flame, 

 } the lantern was placed on a ftand under a large glafs re- 

 ; ceiver ftanding in water, which was of fuflicient capacity to 

 enable the candle to burn for fome minutes. A quantity of 

 1 fire-damp was thrown in from a bladder, fo as to render the 

 I atmofphere explofive. As the fire-damp mixed with the 

 I air, the flame of the taper gradually enlarged till it half 

 I filled the lantern; it then gradually diminifhed, and was fud- 

 ] denly extinguifhed without the flighteft explofion. The air 

 ! in the receiver was found after the experiment to be highly 

 ! explofive. 



Sir H. Davy then introduced into a glafs jar, containing 



an explofive mixture of one part fire-damp and ten parts of 



air, a lighted lantern, to which air was fupplied by two glafs 



'tubes one-tenth of an inch in diameter, and half an inch 



llong. The taper burned at firft with a feeble light, the 



'flame foon became enlarged, and was then extinguifhed. 



!Thefe experiments were feveral times repeated with a con- 



flancy of refult. It is evident, he fays, from hence, that it 



' is only neceffary to ufe air-tight lanterns fupplied with air 



from tubes or canals of fmall diameter, or from apertures 



.covered with wire-gauze, placed below the flame, through 



'which explofions cannot be communicated, and having a 



chimney at the upper part on a fimilar fyftem for carrying 



off the foul air. 



This principle fir H. Davy adapted to a variety of glafs 

 lanterns, in which the air was admitted through fmall aper- 

 itures or wire-gauze, with a top protefted by the fame. 

 Theie lanterns, however they might have anfwered for ex- 

 iperiments in the laboratory, were not, however, well fitted 

 ;for praftical ufe; for befides the frangibihty of common 

 glafs, which expofed the miner to explofions from the en- 

 ilargement of the flame, the glafs was liable to become heated 

 I and to break, however ftrong it might be made. This in- 

 I convenience was, however, removed by the fubftitution of a 

 icylinder of fine wire-gauze, forming a clofe lamp or lantern, 

 I into which the air is admitted, and from which it paffes 

 : through very fmall apertures. In the firft experiments, the 

 [wire was of brafs the ^irth part of an inch in thicknefs, and 

 'the apertures were not more than the -rT^th part of an inch ; 

 Ithis was found to ftop explofions as well as the long tubes or 

 |canals,and to admit a free current of air. The wire-gauze lamp, 

 jin its prefent improved form, is the moft fimple and portable 

 Ithat has yet been introduced. P/ate V. Jig. 5. Geology, re- 

 Iprefents the lamp as at prefent ufed ; a reprefents the fin- 

 jgle cylinder of wire-gauze ; the foldings aaa muft be very 

 Iwell doubled and failened by wire. If the cylinder be of 

 Itwilled gauze, the wire fhould be at leaft of the one-fortieth 

 |Of an inch of iron or copper, and thirty in the warp, and 

 . fixteen or eighteen in the weft. If of plain wire-gauze, the 

 I Vox-. XXXVIII. 



wire fhould not be lefs than one-fixtieth of an inch in thick- 

 nefs, and from twenty-eight to thirty both warp and weft ; 

 i reprefents the fecon'd top, which fits upon a ; c reprefents a 

 cylinder of brafs, in which the wire-gauze is faftened by a 

 fcrew, to prevent its being feparated from the lamp by any 

 blow ; c is fitted into a female-fcrew, which receives the main- 

 fcrew b of the lamp/, furnifhed with its fafe-trimmer h, and 

 fafe-feeder for oil /. 



Lamps on the fame principle were conftrufted, in which 

 the cylinder is made of copper of one-fortieth of an inch in 

 thicknefs, perforated with longitudinal apertures of not 

 more than one-fixteenth of an inch in length, and the one- 

 thirtieth in breadth. {See P/ate I. Jig. 6. Geology.) In 

 proportion as the copper is thicker, the apertures may be 

 increafed in fize. Tliis form of the lamp may be proper 

 where fuch an inftrument is only to be occafionally ufed, but 

 for the general purpofe of the collier, fir H. Davy ftates 

 that wire-gauze is much fupcrior from its flexibility, and the 

 eafe with which new cylinders are introduced. 



To this lamp a valuable addition has been lately made 

 by the application of a lens before the flame, to condenfe 

 the rays of fight, and direft them to any particular fpot. 

 It has the farther advantage of protefting that part of the 

 wire-gauze from coal-duft, by which it is liable to be 

 choaked and obfcured in a few hours. 



In fubfequent experiments,\ fir H. Davy difcovered that 

 much thicker wires and larger apertures might be ufed 

 than were at firft applied. This gave to the lamp greater 

 ftrength, and tranfmitted more fight. 



Gauze made of brafs wire ^^-oth of an inch in thicknefs, 

 and containing only loo apertures in the fquare inch, did 

 not communicate explofion in a mixture of one part coal-gas 

 and twelve of common air, fo long as the wire was cool ; 

 but as foon as the top became hot an explofion took place. 

 A quick lateral motion alfo enabled it to communicate ex- 

 plofion. With 196 apertures to the fquare inch, the ex- 

 plofion was not communicated till the wire became ftrongly 

 hot. 



Iron wire-gauze, containing 240 apertures to the fquare 

 inch, was fafe in explofive mixtures of coal-gas, till it be- 

 came ftrongly red-hot at the top. 



Iron wire-gauze, of 576 apertures to the fquare inch, or 

 the -rrih part of an inch each in diameter, appears, fays 

 fir H. Davy, to be fafe under all circumftances, in explo- 

 five mixtures of coal-gas. With very fine wire-gauze, 

 mixtures of oxygen and hydrogen gafes may be burned 

 without explofion until the brafs wire begins to melt. 



The explanation which fir H. Davy gives of the effeSt 

 of wire-gauze, and fmall tubes in arrefting the progrefs of 

 flame, is as follows : — Thefe refults are beft explained 

 by confidering the nature of the flame of combuftible bodies, 

 which in all cafes muft be confidered as the combuftion of 

 an explojive mixture of inflammable gas, or vapour and air ; 

 for it cannot be regarded as a mere combuftion at the fur- 

 face of contaft of the inflammable matter : and the faft is 

 proved by holding a taper, or a piece of burning phofphorus, 

 within a large flame made by the combuftion of alcohol ; the 

 flame of the candle, or of the phofphorus, will appear in 

 the centre of the other flame, proving that there is oxygen 

 even in its interior part. 



The heat communicated by flame muft depend upon its 

 mafs : this is fhewn by the fad, that the top of a flender 

 cylinder of wire-gauze hardly ever becomes dull-red in the 

 experiment on an explofive mixture ; whilft in a larger 

 cyhnder made of the fame material, the central part of the 

 top foon becomes bright-red. A large quantity of cold air 

 throwa upon a fmall flame, lowers its heat beyond the 

 4 A explofive 



