384 Prof. Bischof on the Employment of the Safety-Lamp 



While in the appai'atus, the cylinders having 104 meshes 

 to the square inch, were found perfectly safe, a cylinder of 

 184 meshes, and 28 lines in diameter, effected an explosion ; 

 the reason of this unequal result, no doubt, depending on the 

 circumstance that the apparatus contains 2\ cubical feet of 

 explosive mixture, but the excavation 233 cub. feet. From 

 this is to be seen the' importance of making experiments in such 

 large spaces, in order to prove the security of the safety- 

 lamps. 



Similar experiments were also instituted in an excavation 

 made in the coal-strata of Wellesweiler. The phenomena 

 were in general the same, but the results rather different, 

 though strictly in accordance with the results of the chemical 

 analysis. The lamp No. 8 was quite safe, but No. 9 and No. 

 10 produced an explosion. No 13 likewise produced instantly 

 an explosion ; therefore these three lamps, which were quite 

 safe in the former excavation, produced in the latter an ex- 

 plosion. 



So large as these excavations were, it is nevertheless to be 

 remarked, that the experiments give sufficient results only 

 when the disengagement of the fire-damp from between beds 

 of coal takes place in the same proportion as is consumed by 

 burning the safety-lamps. On the contrary, the vehemence 

 of the effects gradually decreases, and no safety-lamp can 

 produce an explosion, as it would have done provided the ex- 

 plosive mixture had been there in its strongest form. 



The officers of mines, who made the latter experiments 

 enumerated, have had a favourable opportunity of inquiring 

 into the circumstances taking place when the fire-damp is in 

 violent motion. 



A gallery 35 feet in length, 5 feet in height, and 4 feet in 

 breadth, rising at an angle of 20 degrees, was filled with 

 about 300 cubical feet of explosive mixture. Against this 

 gallery another one was carried. Through the intervening 

 ■space between these two gallex-ies a hole of 1 inch in diameter 

 and 40 inches in length was bored and closed up by a stopper. 

 On approaching a safety-lamp of 900 apertures to the square 

 inch to the hole, and on opening the stopper, the presence of 

 -fire-damp was ascertained by the flame being increased nearly 

 •by one inch. But the streaming of the air was so vehement, 



