FIRE-DAMP WILL ()' THE WISP. 



that the more carbon the gas is charged with the whiter and 

 brighter is the name. 



17. There are two sorts of carburetted hydrogen, one of which 

 contains twice as much carbon as the other : the one called light 

 carburetted or proto-carburetted hydrogen, and the other heavy 

 carburetted or bi- carburetted hydrogen, or olefiant gas. 



18. In light carburetted hydrogen 6 parts, or more exactly 6'12 

 parts by weight of carbon are combined with 2 of hydrogen, and heavy 

 earburetted hydrogen contains twice that proportion of carbon. 



Light carburetted hydrogen is a little more than half the weight 

 of its own bulk of common air. When pure it has no odour ; and it 

 burns with a yellowish flame much more him in mis than that of 

 pure hydrogen. Like pure hydrogen it forms a highly explosive 

 mixture when combined in a certain proportion with common air, 

 or, more properly, with the oxygen of common air, since the azote 

 has no influence on the phenomenon. 



19. It is this gas which, under the name of FIKE-DAMP, produces 

 occasionally such disastrous explosions in coal mines. Being con- 

 tained in large quantities in the fissures and interstices of the seams 

 of coal, it issues from them in the workings of the mines, and being 

 one half lighter than common air, it first collects at the top of the 

 working. After a certain time, by a common property of all 

 gases, it mixes with the air, and attains occasionally that propor- 

 tion which renders it explosive. If a light be brought into it 

 in this state an explosion takes place, producing those destructive 

 consequences to the operatives who happen at the moment to be 

 present, with the details of which the public has been so often 

 rendered familiar. 



20. This gas is also that which over marshy ground and stagnant 

 pools produces the appearance called WILL o' THE WISP, JACK o' 

 LANTHORN, or ignis fatuus. The gas is produced by the decompo- 

 sition of vegetable and animal, matter, and rising from the ground or 

 from the water is spontaneously ignited. 



21. It is easy to verify this by 

 actually collecting the gas from 

 any stagnant pool. For this 

 purpose, take a common funnel 

 used for decanting liquors, and 

 a bottle or beer glass ; immerse 

 the latter in the water, and, 

 when it is filled, invert it under 

 the water and raise it above the 

 surface, keeping the mouth under 



the water. Then bring the inverted funnel under its mouth, the 

 neck entering the bottle or glass ; agitate the funnel, and the gas 



199 



