1234
THEORY AND TRACTICE OF ENGINEERING.
Book II.
oven for 6 or 8 hours, when the plate which closes the mouth of the retort is withdrawn,and a volume of flame pours out; after this the residue, which is coke, is drawn out by
means of iron bars with crooked ends, and water thrown upon it, or it is allowed todescend into a place prepared to receive it.
The quantityof coke obtainedafter distillationvaries, as coalloses from 20 to35 per cent. ; it isusually, however,about half asmuch more thanthe bulk of coalthrown into theretorts, a bushelyielding 1^ bush-els of coke. Thequantity of coalrequired to heata retort is abouta fifth of thequantity withwhich they arecharged, and 1cwt. yields from300 to 500 feetof gas.
Great attentionis required in socarbonising ordistilling pit coal,that the carbu-retted hydrogenmay be producedin the largestquantity; andupon the eco-nomy and carecarried into this
operation depend the successful results of any establishment undertaking to light acity. As soon as the retort into which the coals are put to undergo decomposition becomesred-hot, atmospheric air and steam are given off, and the tar is distilled from it, togetherwith hydrogen and ammonia, in the state of gases, which continue to be evolved as long asthe retort is kept up to this heat; when this is increased, the pyrites of the coal yieldssulphurous acid, which is found united with ammonia; the residuum after distillation iscarbonised coal or coke.
The first gas that comes off gives a very feeble light; that produced at a vivid redheat consists of bicarburetted hydrogen or olefiant gas of the best quality, and affords thebrightest light: in every 100 measures obtained from good coal, the products at the firstgiving out are : —
t•
— i
JX
1 f
A '
-A
t s'
4\ Ls=
LZZ
n i
Fig. 1941.
TRANSVERSE SECTION OP RETORTS.