p. XX.
1233
Some retorts are in tlie form shown in fig. 19*11. and about7 feet 6 inches in length, 18 inches in width, and 1 foothigh in the clear; such are said to yield in the shoitesttime the greatest quantity of gas.
'I'hose that arc cylindrical vary from 8 to 6 feet inlength, and are about 12 inches in diameter; this form ispreferred as being the less expensive, but there are manyobjections to it, particularly from its not allowing the coalwith which it is charged to lie equally thick throughout:in the middle it must lie deeper than towards the sides; itis important that every part of the coal should be equallyacted upon at the same time ; this the cylindrical retorts donot provide for in the same manner as those which haveflatter bottoms.
Whatever form is given to the retorts they are castclosed at one end, and at the other they are fitted with
FJg. 1937. SECTION OF RETORT-HOUSE,
mouth-pieces, also made of iron, into which is fixed theconducting pipe, which carries away the gas as it rises fromthe coal.
The cover or lid requires to be well closed: this is ac-complished by an iron frame, through which a long screwpasses to the centre of the cover, where it enters ; by thismeans the retorts can be closed immediately they arecharged with coal: the joints round the cover are closedmore perfectly by the application of a lime-lute, whichprevents the gas as it is generated from making any escape.
These retorts are liable to accidents : they seldom lastmore than six months, and often not so long; for theyindicate decay both on the out and inside, the former causedby the heat, and the other by the action of the coal itself.
Fig.1933.
ELEVATION OF KETORT-HOUSE.
The iron appears to Increase in bulk,and in time becomes soft, resemblingfinely laminated black chalk. Par-ticular attention is required fortheir setting in large establishments:several are set in one frame or oven,with the fireplaces beneath them; theflues are so contrived that there is notonly an equal distribution of heat, butit is sufficient to decompose allthe coal put into them, which if notproperly done, all the volatile substanceswill not be liberated, and a loss willbe proportionately sustained : each retortis usually charged, after being pro-perly heated, with a bushel' of coal,thrown into it by a long semicirculariron shovel, or scoop, which spreads itthroughout into a thin layer; this remainssubjected to the action of the heat of the
4 K
Ftto.vr or furnace.