WIRE-GAUZE SAFETY-LAMP. 



that as an approximation to a valuable difcovery, Mr. Ste- 

 phenfon's lamp entitled him to the patronage and fupport 

 which he has received. It ought alfo to be recoUefted that 

 Dr. Clanny and Mr. Stepheiifon both laboured under the 

 difadvantage of living at a diftance from the refidence of in- 

 genious praaical mechanics to execute their inventions in the 

 moft fimple, cheap, and portable manner ; an advantage only 

 to be obtained in the neighbourhood of the metropolis, or 

 of large mechanical manufadories. 



Sir H. Davy, after afccrtaining that the fire-damp, or in- 

 flammable air in coal-mines, is the light carburetted hydrogen 

 gas, as ftated by other chemifts, proceeded to examme ac- 

 curately its combuftibility and explofive nature. When one 

 part of fire-damp was mixed with one of common air, the 

 mixture burned on the approach of a taper, but did not 

 explode. Two of air and three of fiie-damp produced 

 fimilar refults. When four of air and one of fire-damp were 

 expofed to a Ughted candle, the mixture being in the quan- 

 tity of fix or feven cubic inches in a narrow-necked bottle, 

 the flame defcended to the bottom, but there was no noife. 

 One part of gas inflamed with fix parts of air in a fimilar 

 bottle, producing a flight whiftling found. One part of 

 gas with three of air rather a louder found. One part with 

 ten, eleven, twelve, thirteen, and fourteen parts, ftill in- 

 flamed, but the violence of the combuftion diminiihed. In 

 one part of gas and fifteen parts of air, the candle burned 

 without explofion, with a greatly -enlarged flame. The fame 

 effeft was obferved, but in a gradually diminiihing ratio, as 

 far as thirty parts of the gas to one of common air. The 

 mixture which feemed to pofl"efs the greateft explofive 

 power was feven or eight parts of air to one of gas ; but 

 the report produced by fifty cubic inches of this mixture 

 •was lefs than that produced by one-tenth of a mixture con- 

 fiding of two parts of common air and one of pure hy- 

 drogen. 



It was alfo very important to afcertain the degree of heat 

 required to explode the different mixtures of fire-damp. A 

 common eledlrical fpark, he found, would not explode five 

 parts of air and one of fire-damp, though it exploded fix 

 parts of air and one of the latter gas. Very itrong fparks 

 from the difcharge of the Leyden jar feemed to have the 

 fame power of exploding different mixtures of the gas, 

 as the flame of a taper. Well-burned charcoal, ignited to 

 the flrongeft heat, did not explode any mixtures of the gas ; 

 and when a fire of the fame charcoal, which burned without 

 flame, was blown to whitenefs by an explofive mixture with- 

 out producing inflammation. An iron rod at a red or 

 even at a white heat did not inflame explofive mixtures of 

 the gas ; but when in brilliant combuftion it produced that 

 effea. 



The flame of gafeous oxyd of carbon, as well as of ole- 

 fiant gas, exploded the mixtures of the fire-damp. 



In refpeft of combuftibility, fays fir H. Davy, the fire- 

 damp differs materially from the other common inflammable 

 gafes. defiant gas, when rendered explofive by a mix- 

 lure of common air, is fired both by charcoal and iron, 

 heated to a dull rednefs. Gafeous oxyd of carbon, which 

 explodes with two parts of air, is hkewife inflammable by 

 hot iron or charcoal. And hydrogen, which explodes when 

 mixed with three-fevenths of air, takes fire at the loweft 

 vifible heat of iron or charcoal ; and the cafe is the fame 

 vnth fulphuretted hydrogen. 



The importance of thefe experiments is too obvious to 

 require illuftration. Having afcertained the above faft?, fir 

 H. Davy proceeded to examine the degree of expanCon of 

 mixtures of firedamp and air during their explofion, and 

 likewiCe their power of communicating flame through aper- 



tures to other explofive mixtures. It is to this latter part 

 of fir H. Davy's experiments and its application to fafety- 

 lamps, that the controverfy relpefting the priority of the 

 difcovery refers. 



When fix parts of air and one of fire-damp were exploded 

 over water by a ftrong eleftrical fpark, the explofion was 

 not very ftrong ; and at the moment of the greateft expan- 

 fion, the volume of the gas did not appear to be increafed 

 more than one-half. In exploding a mixture of one part 

 gas from the diftillation of coal, and eight parts of air in a 

 tube one-quarter of an inch in diameter, and one foot long, 

 more than a fecond was required before the flame reached 

 from one end of the tube to the other, and he could not 

 make any mixture explode in a glafs tube one-feventh of an 

 inch in diameter ; and this gas was more inflammable than 

 fire-damp, as it confifted of carburetted hydrogen mixed 

 with fome defiant gas. 



In exploding mixtures of firedamp and air in ajar, con- 

 nefted with the atmofphere by an aperture of half an inch, 

 and connefted with a bladder by a ftop-cock having an aper- 

 ture of about one-fixth of an inch, the flame paffed into the 

 atmofphere, but did not communicate through the ftop-cock 

 fo as to inflame the mixture in the bladder ; and in compar- 

 ing the power of tubes of metal and thofe of glafs, it ap- 

 peared that the flame pafTed more readily through tubes of 

 glafs of the fame diameter, and that explofions were flopped 

 by metallic tubes of one-fifth of an inch, when they were 

 one inch and a half long ; and this phenomenon probably 

 depends upon the heat loft during the explofion, in contaft 

 with fo great a cooling furface, which brings the tempera- 

 ture of the firft portions exploded below that required for 

 firing the other portions. 



Metal is a better conduftor of heat than glafs ; and it has 

 been already fhewn, that the fire-damp requires a very ftrong 

 heat for its inflammation. 



A mixture of the gas with air, he alfo found, would not 

 explode in metaUic canals or troughs when their diameter 

 was lefs than one-feventh of an inch, and their depth con- 

 fiderable in proportion to their diameter, nor could explo- 

 fions be made to pafs through fuch canals. 



Azote and carbonic acid, even in fmall proportions, dimi- 

 nifhed the velocity of inflammation in explofive mixtures of 

 fire-damp. Azote, when mixed in the proportion of one to 

 fix of an explofive mixture containing twelve of air and 

 one of fire-damp, deprived it of its power of explofion ; 

 when one part of azote was mixed with feven of an explo- 

 five mixture only, a feeble blue flame paffed through it. 



One part of carbonic acid to feven of an explofive mix- 

 ture deprived it of the power of exploding ; fo that its 

 effefts are more remarkable than thofe of azote, probably 

 in confequence of its greater capacity for heat, and pro- 

 bably likewife of its higher condufting power connefted 

 with its greater denfity. 



The confideration of thefe various fafts, fir H. Davy in- 

 forms us, led him to adopt a form of lamp in which the 

 flame, being fupplied with only a limited quantity of air, 

 fhould produce fuch a quantity of azote and carbonic acid 

 as to prevent the explofion of the fire-damp ; and which, by 

 the nature of its apertures for giving admittance and exit 

 to the air, (hould be rendered incapable of communicating 

 any explofion to the external air. 



If in a clofe lantern fupplied with a fmall aperture below 

 and another above, a lighted lamp having a very fmall wick 

 be placed, the natural flame gradually diminifhes, till it ar- 

 rives at a point at which the fupply of air is fufficient for 

 the combuftion of a certain fmall quantity of oil ; if a 

 lighted taper be introduced into the lantern through a fmall 



door 



