The gases issuing from the producers are led through a rectangular chamber partly filled with water, which is thrown up in a fine spray by revolving beaters so as to fill the whole area of the chamber.  This water, of course, becomes hot; a certain quantity of it evaporates, the spray produced washes all dust and soot out of the gases, and also condenses the fixed ammonia.  The water thus becomes, to a certain degree, saturated with ammonia salts, and a certain portion of it is regularly removed from the chamber and distilled with lime to recover the ammonia.

[Illustration:  Longitudinal Section of Plant for obtaining Ammonia from Gas Producers.

Cross Section through Gas Producers.]

This chamber is provided with water lutes, through which the tar condensed in it is from time to time removed.  From this chamber the gases, which are now cooled down to about 100 deg.  C., and are loaded with a large amount of water vapor, are passed through a scrubber filled with perforated bricks, in which the ammonia contained in the gases is absorbed by sulphuric acid.  In this scrubber a fairly concentrated solution of sulphate of ammonia containing 36 to 38 per cent. is used, to which a small quantity of sulphuric acid is added, so that the liquid leaving the scrubber contains only 2.5 per cent. of free acid.  This is necessary, as a liquid containing more acid would act upon the tarry matter and produce a very dark-colored solution.  The liquid running from the scrubber is passed through a separator in which the solution of sulphate of ammonia separates from the tar.  The greater portion of the clear liquid is, after adding a fresh quantity of acid to it, pumped back through the scrubber.  A certain portion of it is, after treatment with a small quantity of heavy tar oils, which take the tarry matter dissolved in it out, evaporated in conical lead-lined pans furnished with lead steam coils, and which are kept constantly filled by the addition of fresh liquor until the whole mass is thick.  This is then run out on a strainer and yields, after draining and washing with a little water, a sulphate of ammonia of very fair quality, which finds a ready sale.  The mother liquor, which contains all the free acid, is pumped back to the scrubber.

The gas on entering this scrubber contains only 0.13 volume per cent. of ammonia, and on leaving the scrubber it contains not more than one-tenth of this quantity.  Its temperature has been reduced to 80 deg.  C., and is fully saturated with moisture, so that practically no condensation of water takes place in the scrubber.  The gas is next passed through a second scrubber filled with perforated wood blocks.  In this it meets with a current of cold water which condenses the steam, the water being thereby heated to about 78 deg.  C. In this scrubber the gas is cooled down to about 40 deg.-50 deg.  C., and passes from it to the gas main leading to the various places where it is to be consumed.  The hot water obtained in this second scrubber is passed through a vessel suitably constructed for separating the tar which is mixed with it, and is then pumped through a third scrubber, through which, in an opposite direction to the hot water, cold air is passed.  This is forced by means of a Roots blower through the scrubber into the producer.