A$i On the Fire-damp of Cool Mines, and on Melliods 



deep, and at least two inches in circumference ; or provided the 

 wire gauze had apertures of only -^--.-^ of an inch. When twelve 

 metallic tubes were emjjloyed as the medium of communication, 

 .•)• of an inch in diameter and an inch long, the explosion was 

 comnmnicated by them into the bladder. Four glass tubes of 

 the -pg- of an inch in diameter and 2 inches long, did not com- 

 municate the explosion ; but one of this diameter and length 

 produced the effect. The explosion was stopped by a single tube 

 ■5I5-* of an inch in diameter, when it was three inches long, but 

 not when it was two inches long. 



The explosion was stopped by the metallic gauze of -j-i-^ when 

 it was placed between the exploding vessel and the bladder, 

 though it did not present a surface of more than half a square 

 inch, and the explosive mixture in the bladder in passing through 

 it to supply the vacuum produced in the glass vessel, burnt on 

 the surface exposed to the glass ^•cssel for some seconds, pro- 

 ducing a murmuring noise. 



A circular canal -^ of an inch in diameter, and an inch and a 

 half in circumference, and l-^V of an inch deep, communi- 

 cated explosion ; but four concentric canals, of the same depth 

 and diameter, and of which the smallest was two inches in 

 diameter, and separated from each other only by their sides, 

 which were of brass, and about Vtt "f ^'^ i"'^!' J" thickness, did 

 not suffer the explosion to act through them. 



It would appear then, that the smaller the circumference of 

 the canal, that is, the nearer it approaches to a tube, the greater 

 must be its dejith, or the less its diameter to render it safe. 



I did not perceive any difference in these experiments, when 

 the metals of the apertures were warmed by repeated explosions : 

 it is probable, however, that considerable elevation of tempera- 

 ture Vvould increase the power of the aperture to pass the ex- 

 plosion ; but the difference between the temperature of flame, 

 and that marked on our common mercurial scale, is so great, 

 that the addition of a hw degrees of heat probablv does not 

 diminish perceptibly the cooling power of a metallic surface, 

 with regard to flame. 



By diminishing the diameter of the air canals, their j)ower of 

 passing the explosion is so much diminislied that their depth 

 and circumference may be brought extremely low. I found that 

 flame would not pass through a canal of the ^- of an inch in 

 diameter, when it vyas ~ of an inch deep, and forming a cylinder 



* These results appear at first view contradictory to tliose mentioned 

 in page 449. But it must be kept in view, that the first set ot' experiments 

 were made in tubes open in tlie air, and the last in tules expustd to the 

 whole force of air explosion, and connected only with close vessels filled 

 with cxplosi\-e mixtures. 



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