obtained by
heating samples of the different coals in vacuo for several hours at the
temperature of boiling water:--

+------------+------------------+---------+----------------------------------+
| | | Volume | Composition in Volumes per cent. |
| Quality. | Colliery. | per ton +---------+-------+------+---------|
| | | in cub. | Carbonic| | Marsh|Nitrogen.|
| | | ft. | Acid. |Oxygen.| gas.| |
+------------+------------------+---------+---------+-------+------+---------+
| Bituminous | Cwm Clydach | 19.72 | 5.44 | 1.05 | 63.76| 29.75 |
| " | Lantwit | 14.34 | 9.43 | 2.25 | 31.95| 56.34 |
| Steam | Navigation | 89.62 | 13.21 | 0.49 | 81.64| 4.66 |
| Anthracite | Bonville's Court | 198.95 | 2.62 | .. | 93.13| 4.25 |
+------------+------------------+---------+---------+-------+------+---------+

In one instance about 1% of hydride of ethyl was found in the gas from a
blower in a pit in the Rhondda district, which was collected in a tube
and brought to the surface to be used in lighting the engine-room and
pit-bank. The gases from the bituminous house coals of South Wales are
comparatively free from marsh gas, as compared with those from the steam
coal and anthracite pits. The latter class of coal contains the largest
proportion of this dangerous gas, but holds it more tenaciously than do
the steam coals, thus rendering the workings comparatively safer. It was
found that, of the entire volume of occluded gas in an anthracite, only
one-third could be expelled at the temperature of boiling water, and
that the whole quantity, amounting to 650 cub. ft. per ton, was only to
be driven out by a heat of 300 deg. C. Steam coals being softer and more
porous give off enormous volumes of gas from the working face in most of
the deep pits, many of which have been the scene of disastrous
explosions.

The gases evolved from the sudden outbursts or blowers in coal, which
are often given off at a considerable tension, are the most dangerous
enemy that the collier has to contend with. They consist almost entirely
of marsh gas, with only a small quantity of carbonic acid, usually under
1%, and from 1 to 4% of nitrogen.

Fire-damp when mixed with from four to twelve times its volume of
atmospheric air is explosive; but when the proportion