4.')6 Ow the Fire-damp of Coal-Mines ^ a?id Methods 



in the mixed gas, and the ventilation must be greater to free the 

 mine from the choke-damp so generated, than from the original 

 fire-damp. 



It does not appear, by what I have learnt from the miners, 

 that breathing an atmosphere containing a certain mixture of 

 fire-damp near or even at the, explosive point, is attended with 

 any bad consequence, I ascertained that a bird lived in a 

 mixture of equal parts of fire-damp and air ; but he soon began 

 to show syn)ptoms of suffering. I found a slight head-ache 

 produced by breathing for a few minutes an explosi\ e mixture of 

 fire-damp and air ; and if merely the health of the miners be 

 considered, the fire-damp ought always to be kept far below the 

 point of its explosive mixture. 



Miners .sometimes are found alive in a mine after an explosion 

 lias taken place : this is easily explained, when it is con- 

 sidered that the inflammation is almost alwa\s limited to q 

 particular spot, and that it mixes the residual air with much 

 common air ; and supposing 1 of fire-damp to 13 of air to be 

 exploded, therewill still remain nearly 4- of the original quantity of 

 oxygen in the residual gas ; and in some experiments, made 

 sixteen years ago, I found that an animal lived, though with 

 suffering, for a short time, in a gas containing 100 parts of 

 azote, fourteen parts of carbonic acid, and seven parts of ox- 

 ygen. 



Explanation of the Plate. (Plate VIII.) 



Fig. 1. Represe)\ts the safe lantern, with its air-feeder and 

 chinmev furnished with safety metallic canals. It contains 

 about a quart of air. The sides are of horn or glass, made air- 

 tight by putty or cement. A. is the lamp through which the 

 circular air-feeding canals pass : they are 3 concentric-hollow 

 cylinders, distant from each other .^ig- of an inch : the smallest is 

 2.T inches in circumference ; their depth is 2 inches. B. is the 

 chimney, containing 4 such canals, the smallest 2 inches in cir- 

 cumference : above it is a hollow cylinder, with a cap to pre- 

 vent dust from passing into the chimney. C. is the hole for 

 admitting oil. D. is along canal containing a wire by which 

 the wick is moved or trimmed. F. is the tube forming a con- 

 nexion between the reservoir of oil and the chamber that supplies 

 the wick with oil. F. is the rim round the bottom of the lan- 

 tern to enable it to bear motion. 



Fig. 2. is the lamp of fig. 1., of its natural size, the refe- 

 rences to the letters are t'le same. 



Fig. 3. is a common chimney which may be used in the lan- 

 tern ; but the safety chimney doubles security. 



Fig. 



