738 GEOLOGY OF OHIO. 
oval) shaped, though oval shapes are frequently used. The retorts are 
set in “benches” of three to eight retorts to a bench, three to five in 
small works and six to eight in larger works. The benches consist of 
brick arches or ovens, made large enough to contain the number of 
retorts desired to be used. Furnaces are built in the arches under the 
retorts. Dimensions of furnace are usually about 14 inches wide by 
three to four feet long and two feet deep. The retorts are closed at one 
end by being made solid. To the other end is attached a cast-iron 
“mouth-piece,” and is closed by a cast or wrought iron lid, the mouth- 
piece having a circular opening of 4 inches to 8 inches, into which the 
ascension or stand-pipe is placed, which runs up in front of, and above 
the benches and by return bends passes down into the hydraulic main. 
The hydraulic main is usually made of cast-iron, GJ shaped, and is 
filled with water to a point above the center line. The “ dip-pipe” which 
isa continuation of the ascension pipe, dips down into the liquid in 
hydraulic main one-half to an inch in depth. A fire being made in the 
furnace, the retorts are heated up to 1500° or 2000° Fahr. Coal is 
thrown into the retorts and the lids luted on. Gas is immediately dis- | 
engaged from the coal, passes out of the retorts up the ascension pipe, 
down the dip-pipes, bubbles through the water of the hydraulic main, 
and passes off by a pipe leading from the hydraulic main to condensers, 
scrubbers, purifiers, station meter, and on into the gas holder, where it 
is stored for use. To the hydraulic main is attached an overflow for the 
discharge of the tar and water generated from the coal. The scrubbers 
are large iron vessels filled with boards, boulders, coke, twigs of trees, 
or other scrubbing material, which arrests the tar and soot and other 
condensable matter and at least a portion of the scrubber or serubbers 
will have water running through to absorb the ammonia. The con- 
densers are a series of iron pipes surrounded by air or water or large 
vessels made similar to tubular boilers, air or water circulating through 
them, but kept from the gas by the divisions in the vessel. The con- 
densers are expected to cool the gas down to a temperature ranging from 
50° to 70° Fahr. The purifiers are large iron boxes filled with lime or 
some form of oxide of iron, through which gas is forced to percolate, and 
into which the impurities of the gas, sulphur and carbonic acid are 
deposited. The station meter registers the purified gas, which is then 
passed on to the holder for storage. 
The gas-holder is made of light rolled iron, properly supported in- 
cr. 
