COAL AS A RESERVOIR OF POWER. 
16! 
enormous mass of matter has been derived from vegetable 
organizations which have been built up by sunshine. The sun- 
rays which compelled the plants to grow were used by the 
plant, absorbed, imprisoned in the cells, and held there as an 
essential ingredient of the woody matter. The heat, light, 
actinism, and electricity, which are developed when we burn a 
lump of coal, represent exactly the quantity of those forces 
which were necessary to the growth of the vegetable matter 
from which that coal was formed. The sunshine of infinitely 
remote ages becomes the useful power of the present day. 
Let it not, however, be supposed that we employ all the heat 
which is available in our coal. All our appliances, even the 
very best, are so defective that we lose far more than we use. 
A pound of pure coal should evaporate thirteen pounds of 
water ; in practice a pound of coal does not evaporate four 
pounds, even in the most perfectly constructed steam-boilers, 
with the most complete steam-engines, such as have been con- 
structed for pumping water for the Chelsea and the other 
waterworks upon the Thames. 
Numerous attempts have been made to burn our coal so as 
to secure a more effective result than this. There has been 
some advance, the most satisfactory being in the regenerative 
furnace of Mr. Siemens. In this system the solid fuel is con- 
verted into crude gas, this gas is mixed with a regulated quan- 
tity of atmospheric air, and then burnt. The arrangements 
are essentially the gas producer, or apparatus for converting- 
the fuel bodily into a gaseous state ; then there are the regene- 
rators. These are sunk chambers filled with fire-bricks, piled 
in such a manner that a current of air or gas, passing through 
them, is broken into a great number of parts, and is checked at 
every step by the interposition of an additional surface of fire- 
brick ; four of these chambers are placed below each furnace. 
The third essential is the heated chamber , or furnace proper. 
This, the furnace chamber, communicates at each extremity 
with two of the regenerative chambers, and, in directing cur- 
rents of gas and air upwards through them, the two gaseous 
streams meet on entering the heated chamber, where they are 
ignited. The current descends through the remaining two 
regenerators, and heats the same, in such a manner, that the 
uppermost chequerwork is heated to nearly the temperature of 
the furnace, whereas the lower portions are heated to a less and 
less degree, the products of combustion escaping into the 
chimney comparatively cool. In the course of, say, one hour, 
the currents are reversed, and the cold air and gas ascending 
through the two chambers which have been previously heated, 
take up the heat there deposited, and enter into combustion at 
their entrance into the heated chamber, at nearly the tern- 
