4 Sir Humphry Davy on the fire-damp of coal mines , and on 
The Rev. Mr. Hodgson informed me, that on pounding 
some common Newcastle coal fresh from the mine in a cask 
furnished with a small aperture, the gas from the aperture 
was inflammable. And on breaking some large lumps of 
coal under water, I ascertained that they gave off inflammable 
gas.* Gas is likewise disengaged from bituminous shist, 
when it is worked. 
The great sources of the fire-damp in mines are, however, 
what are called blowers, or fissures in the broken strata, 
near dykes, from which currents of fire-damp issue in con- 
siderable quantity, and sometimes for a long course of years.-f 
When old workings are broken into, likewise, they are often 
found filled with fire-damp ; and the deeper the mine the 
more common in general is this substance. 
* This is probably owing to the coal strata having been formed under a pressure 
greater than that of the atmosphere, so that they give off elastic fluid when they are 
exposed' to the free atmosphere : and probably coals containing animal remains, evolve 
not only the fire-damp, but likewise azote and carbonic acid, as in the instance of 
the gas sent by Dr. Clan n y. 
In the Apennines, near Pietra Mala, I examined a fire produced by gaseous matter, 
constantly disengaged from a shist stratum : and from the results of the combustion, 
I have no doubt but that it was pure fire-damp. Mr. M. Faraday, who accompanied 
me, and assisted me in my chemical experiments, in my journey, collected some gas 
from a cavity in the earth about a mile from Pietra Mala, then filled with water, and 
which, from the quantity of gas disengaged, is called Aqua Buja. I analysed it in 
the Grand Duke’s laboratory at Florence, and found that it was pure light hydro-car- 
bonate, requiring two volumes of oxygene for its combustion, and producing a volume 
of carbonic acid gas. 
It is very probable, that these gases are disengaged from coal strata beneath the 
surface, or from bituminous shist above coal ; and at some future period new sources 
of riches may be opened to Tuscany from this invaluable mineral treasure, the use of 
which in this country has supplied such extraordinary resources to industry. 
f Sir James Lowther found a uniform current produced in one of his mines for. 
two years and nine months. Phil. Trans. Vol. XXXVIII. p. 112. 
