gree, 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 i