The air gets heated to about 76 deg.  C. and saturated with moisture at that temperature by its contact with the hot water, and the water leaves this third scrubber cold enough to be pumped back through the second scrubber.  The same quantity of water is thus constantly used for condensing the water vapor in one scrubber and giving it up to the air in the other.  In this way we recover and return to the producer fully two-thirds of the steam which has been originally introduced, so that we have to add to the air, which has thus been loaded with moisture, an additional quantity of steam equal to only one-third of the total quantity required before it enters the producer.  This additional quantity of steam, which amounts to 0.6 ton of steam for every ton of fuel burnt, we obtain as exhaust steam from the engines driving the blowers and pumps required for working the plant.

The gas producers which I prefer to use are of rectangular shape, so that a number of them can be put into a row.  They are six feet wide and 12 feet long inside.  The air is introduced and the ashes removed at the two small sides of the producer which taper toward the middle and are closed at the bottom by a water lute of sufficient depth for the pressure under which the air is forced in, equal to about 4 inches of water.  The ashes are taken out from underneath the water, the producers having no grate or fire bars at all.  The air enters just above the level of the water through a pipe connected with the blower.  These small sides of the producer rest upon cast iron plates lined to a certain height with brickwork, and this brickwork is carried by horizontal cast iron plates above the air entrance.  In this way a chamber is formed of triangular shape, one side of which is closed by the ashes, and thus the air is distributed over the whole width of the producer.

The gas is taken out in the middle of the top of the producer by an iron pipe, and fuel charged in by hoppers on both sides of this pipe.  Between the pipe and the hoppers two hanging arches are put into the producers a certain distance down, and the fuel is kept above the bottom level of these hanging arches.  This compels the products of distillation, produced when fresh fuel is charged in, to pass through the incandescent fuel between the two hanging arches, whereby the tarry products are to a considerable extent converted into permanent gas, and the coal dust arising from the charging is kept back in the producer.

The details of construction of this plant will be easily understood by reference to the diagrams before you.

The fuel we use is a common kind of slack, and contains, on an average, 33.5 per cent. of volatile matter, including water, and 11.5 per cent. of ashes, leaving 55 per cent. of non-volatile carbon.

The cinders which we take out of the producer contain, on an average, 33 per cent. of carbon.  Of this we recover about one-half by riddling or picking, which we return to the producer.  The amount of unburnt carbon lost in the cinders is thus not more than 3 per cent. to 4 per cent. on the weight of fuel used.