THE GAS COALS OF OHIO. 739 
side by angle and T iron and tie rods. The holder is simply a large 
tub or vessel, turned mouth down, and resting in the water of a large 
tank. ‘The gas is conveyed from the station meter in pipes in under the 
tank and up through the water, and escapes above the surface of the 
water, but under the tub or holder, the pressure of the gas raising the 
holder, which is kept perpendicular by guide columns. Another pipe 
will lead from the inside of this holder to the streets and to the buildings 
to be lighted with gas; the weight of the holder giving the pressure 
necessary to force the gas to the burners of the consumer. 
Many pieces of intricate machinery, such as exhausters, governors, 
pressure and vacuum gauges and pressure registers, ete., are left 
undescribed. 
They are valuable and indispensable adjuncts to the economical 
manufacture of gas, but gas can be and is generated, purified, stored and 
distributed without their aid. The more notable improvements of the 
last few years, however, are the general substitution (not recent) of 
the clay for iron retort, enabling the manufacturer to run much higher 
heats; the various plans for dispensing with the dip or seal of hydraulic 
main; improved forms of washers and scrubbers ; the general adoption 
of the iron processes for removing sulphur, instead of using lime; the 
general use of the exhauster to pump the gas from the retorts, and force 
it through the varied apparatus and into the holder. In some of the 
larger works, machinery operated by steam is used for drawing and 
charging retorts, instead of doing this work by hand. ‘The adoption of 
these generative furnaces, by which the retorts are heated with gaseous 
fuel, is perhaps the most important improvement of recent years to gas 
manufacture. In the furnace described on a preceding page, coke is the 
fuel used, the coke being thrown into the furnace with shovels from the 
floor of the retort house. 
There are several forms of the generative furnaces, and they are 
placed in various positions, but generally they are built in a basement 
constructed under the floor of retort house. The furnaces are made 
three to four feet long, twelve to twenty-four inches wide, and three to 
six feet deep. The hot coke is drawn from the retorts and descends into 
the furnace through a chute, which can be closed up air-tight. Suffi- 
cient air is admitted through the grate bars to consume the coke to 
carbonic oxide, which issues through the hot space above the coke up to 
the bottom of the retorts, a distance from three to six feet. Below the 
