98 
country ; and of the substances sublimed from the burning coal-pits at New¬ 
castle in Philosoph. Trans, for 1 676 ” 
In coal-mines, besides the choak-damp, fixed air, the production of open 
as of slow combustion, we find the fire-damp, inflammable gas*, the secret 
product of decomposed water, or of vegetable matters. 
This may be breathed with impunity in a certain state of dilution with 
common air; but if a candle should chance to light it, the whole is instantly 
fired, and the supporter of the flame and his companions meet with an un¬ 
timely and dreadful end.'f' 
But not minerals alone, but other substances also generate a great degree 
of heat. 
The warmth of putrescent dunghills, of the fermenting juices of vege¬ 
tables, and, more than all, the spontaneous firing of hay is well known to 
every one. 
Vegetable decomposition is also, as we shall hereafter shew, when we 
come to the subject of agriculture, greatly accelerated by the power of 
lime. 
This alkaline substance, when it appears in the form of a grey white 
stone, is called quicklime. 
This is most frequently met with in places adjacent to volcanoes. 
When exposed to the action of the air, lime swells, breaks, and falls 
into powder; it then increases greatly in bulk, and is called lime slaked 
in air. 
These changes are more remarkable, and take place more rapidly, when 
the air is in a humid state. 
* This vapour is known in mines by the blue appearance of light, and is seen in flocculent balls 
floating above the pit. These assemble, and forming into one mass produce, when lighted, a terrific 
explosion. The miners hinder these natural balloons from assembling by driving them asunder with 
a fan elevated by a long stick, but when the quantity collected is great, the miners fall on their faces 
on the ground, and set fire to the lighter air above them. In certain mines replete with this air, as 
inflammable aii is not kindled by a spark, and may be breathed with impunity, the miners continue 
to work, whilst a boy keeps turning a wheel which hits upon as many flints as there are opposing 
steels, and procures for them by this means a sufficiency of light. 
f 1 his happened to one of Lord Lonsdale s managers and some other people. As he was ex¬ 
amining some paits of a mine, the boy was bid to hold the candle down and stoop, but, actuated 
by some sudden panic, he rose up, and an explosion taking place they were all burnt to death. 
