1236

THEORY AND PRACTICE OF ENGINEERING.

Book II.

C

compartment to another. In the passage of the gas it is at lastperature of the air, and made to deposit the whole of its tar andliquor, which pass off’ into the tar cistern beneath, where theliquor floats at the top, and is drawnoff by means of pipes placed there forthe purpose; or there are two pumps,one which passes to the bottom, to liftup the tar, and the other enters onlythe part containing the ammonia, whereit can be pumped out, without bring-ing up the tar. A chaldron of coalsyields 1J cwt. of tar, and produces from15 to 18 gallons of ammoniacal liquor.

Other condensers have been intro-duced, which consist of a series ofascending and descending bends ofpipes, where the tar, of two or threequalities, may be drawn off, and theammoniacad liquor easily discharged :it has been estimated that about 10square feet of condenser is required tocool 1 cube foot of gas per minute;and that when 10 cubic feet of ^gas are produced per minute, a (f

cooled down to the tem-ammoniacalammoniacal

90

4

AMMONIACAL liquor

B

M

gnu

t-“-r -f* t

Fig 1943. CONDENSER.

cooling surface is required, equal to 100 squarefeet; or in establishments where 100,000 cubicfeet of gas are produced every 24 hours the con-densing surface must be from 800 to 900 squarefeet.

The Purijier. — As it is necessary to separate the sulphuretted hydrogen and carbonicacid gases, which is not possible by mere cooling, and to clear the coal gas from other

impurities injurious to health, which also corrode the pipes, as it passesthrough them to the burners, and injures the colour of the flame, it is sub-jected to a chemical action, by passing through lime and water, mixedtogether to the consistence of thick, cream ; hence called cream of lime. The

sulphuretted hydrogen and carbonic acid are taken up by the lime, and the water absorbsany ammonia that may remain.