412 MIXED GASES. 



and that the most deplorable accidents have frequently resulted from 

 its explosion.* 



(b.) It probably 'arises from the decomposition of water by the 

 coal, and issues from the crevices of the rocks and of the coal strata, 

 particularly from places called blowers ;f it is but little more than 

 half as heavy as common air, and therefore it occupies first the roof 

 of the mine.f 



2. HISTORY. 



(c.) The first scientific account of the gas of coal mines, was pub- 

 lished in 1806, by Dr. Henry, $ who proved that it is the same as 

 the light carburetted hydrogen. 



(d.) Sir Humphrey Davy, some years later, visited the coal mines 

 in person, descended with the miners into the regions of the fire 

 damp, obtained specimens of the gas and subjected them to a chem- 

 ical examination. || 



(e.) He discovered several important facts, and by a train of in- 

 genious and philosophical reasoning, was led to a happy conclusion 

 in the discovery of the safety lamp. 



* In the Felling Colliery, 92 miners perished at one time, and 23 at another, and 

 in another 57 were killed in the same way. Murray. 



t These are fissures laid open in working the mines. 



t When mixed with the air of the mine, it is said to produce a misty appearance, 

 as I had opportunity of observing at the mines of Newcastle, in England, in Nov. 1805. 

 If the quantity of gas in the mines is small, it is harmless; but if great the consequences 

 are sometimes extensively fatal. The catastrophe proceeds from the extreme in- 

 flammability of this gas, and its disposition to explode when mixed with the atmos- 

 phere. Unhappily, in these dark regions, no work can be done without artificial 

 light. In some places, they work by the feeble sparks produced by rubbing flint 

 against a jagged steel wheel. In other places, they carry a candle or a torch, and 

 whenever the fire is communicated to a large quantity of this gas mixed with 

 common air, the explosion is as sudden and violent as that of gun powder. Some- 

 times, the mine, machinery, and miners are blown up, with the loss of all their 

 works, and of course of the lives of a large proportion of the people. 



If the walls and roof of the mine are so strong as not to give way, the expansive 

 force of the steam and of the elastic vapors rarefied by the sudden heat, forces every 

 thing along the narrow chamber of the mine, as a bullet is driven from a gun. In 

 the mines where the production of this gas is not very rapid, the miners set fire to it 

 frequently, and thus explode it in small quantities without danger. This they do by 

 means of a candle tied to the end of a long pole, which they elevate into those parts of 

 the roof where the gas commonly collects. Sometimes they tie a candle in the mid- 

 dle of a rope, and two men, by pulling the rope at the two ends, bring the candle 

 into contact with the gas. But where it is produced too copiously to be managed in 

 this way, the miners fix wooden pipes all along the roof of the mine, with branches 

 carefully communicating with those places from which the gas issues, and all these 

 pipes are connected with one main shaft which terminates in a chamber where is a 

 fire place with a very tall chimney. Here a fire is constantly maintained, and the 

 rarefaction of the air produces a constant stream from all parts of the mine to this 

 spot, where the gas burns quietly away without injury. 



When the inflammable air is very copious, it is said to burn at the top of the chim- 

 ney, and to produce heat enough to maintain the combustion without any additional 

 fael. Nichok?on's Jour. XIX, 149. 



|| Phil. Trans. 1816; History of the Safety Lamp, 1818; Phil. Mag. I, 50. 387. 



