DURHAM AND NORTHUMBERLAND. 10(J

pit-men, an explosion follows, commensuratewith the quantity of hydrogen gas, which isfrequently very considerable.*

“ The great danger of these explosions, evenwhen every precaution has been taken, is ma-nifest by their frequency, and indeed it maybe expected that an explosion will take placeby means of a lighted candle the instant thatthe hydrogen gas amounts to one-twelfth partof the atmospheric air present, and that asimilar effect will follow at all proportions fromone-sixth to one-twelfth.

“ When ventilation, by the methods in ge-neral use, is found insufficient to carry off thefire-damp as it arises in coal mines, largepumps are employed at the top of the shaftfor that purpose, which are worked by steam-engines. So frequent and instantaneous arethe changes in the proportions of inflammableair from accidental circumstances, that it wouldbe impossible at all times to ascertain, by a che-mical process, at all parts of the mine whendanger is impending ; for frequently the great-est differences of proportions exist at the sametime in different parts of such extensive works

* The account of the explosions as contained in Dr.Clanny’s paper is here omitted, as they are described morefully in the foregoing pages.