60 mSTORY OF 



cue him if possible, from that dreadful situation ; though a little 

 reflection might have shown her it was then too late. But no- 

 lliiiig could deter her; she ventured forward, and had scarce 

 touched him with her hand, when the damp prevailed, and the 

 misguided, but faithful creature, fell dead by his side. * 



* The coal-mines of Great Britain were wrought on a very limited scale, 

 and with comparatively little system, till after the beginning of the eighteenth 

 century. It was not till the iutrodiictiou of the steam-engine, for drawing 

 water in the first place, and coals afterwards, that the coal mines began to be 

 wrought on an extensive scale ; even to this period the ventilation of mines 

 was conducted in a very rude, uncertain, and irregular manner, and for many 

 years afterwards. Every bed of coal abounds less or more with deleterious 

 air, which is of two kinds ; the one is specifically heavier, the other lighter, 

 than common air ; the natural consequence of which is, that the one rests in 

 the deepest or lowest places, the other, from its levity, ascends to the highest 

 places of the mine. The first is known by the common provincial names of 

 choak damp, black damp, styth, or bad air ; the other is known by the name 

 of foul air, fire damp, or inflammable air. The one is the carbonic acid, the 

 other tliecarburetted hydrogen gas of the chemist. The precise qualities of the 

 carbonic acid of coal mines, have been comparatively little attended to, as its 

 destroying powers have not operated extensively. The nature and composi- 

 tion of the carburetted hydrogen have closely engaged the attention of phi. 

 losophers for the last ten years. According to the best authorities these gasea 

 are of the following specific gravity and weight. 



Weight of 100, 

 Spec. Grav. Cubic inches. 



Carbonic acid 1.518 46.313 



Carburetted hydrogen 0.555 16.99 



Hydriigen 0.074 2.230 



The common air being reckoned unity, the temperature at 60, and barometer 

 at 30 inches. According to Dr Thomson, the component parts of carburetted 

 hydrogen are. 



Carbon 72 



Hydrogen 28 



100 

 In which there is always a mixture of carbonic acid. 



Various theories have been brought forward regarding the formation of 

 these gases, but more particularly of the carburetted hydrogen : both of tliem 

 flow or exude from the cutters, fissures, and minute pores of the coal ; and 

 when in small quantity icg-the forehead of a mine in solid coal, they make a 

 hissing noise. The carbonic acid seldom comes off very suddenly in large 

 quantities. From its weight it is not liable to a sudden change of place, and 

 though it is invisible, its line of division from the common atmospheric air is 

 most distinctly found by approaching it with a lighted candle or lamp ; for 

 though the candle burns with its ordinary brightness at the distance of three 

 inches from the carbonic acid, the instant it is placed within this air, it is 

 suddenly extinguished ; it produces the same instant effect upon the strong. 



