tower 35 ft. high by 6 ft. 6 in. in diameter, with perforated shelves,
into which steam is blown from below, the liquor passing downward. The
bicarbonate is decomposed, pure carbonic acid being given off. This is
passed through a scrubber and into a gas holder ready for use. The
liquor, which has now returned to the state of simple carbonate of
sodium, only requires cooling to be ready to absorb a fresh lot of
carbonic acid gas. The cooling is effected in a tower packed loosely
with bricks, the hot liquor trickling down against a powerful current
of air blown in from below. Liquor has been cooled in this way, in
once passing through the tower, from 220° Fahr. to 58° Fahr., but of
course the exact cooling obtained depends more or less on the
temperature of the atmosphere.

The next stage of the process, if we follow on after the preparation
of the pure carbonic acid, is the employment of the gas for the
decomposition of the ammonium sulphide absorbed in a brine liquor as
above explained. The brine and ammonium sulphide are contained in what
is known as a "Solvay tower," provided with proper means for
dispersion and absorption of the carbonic acid gas. The precipitated
bicarbonate of sodium is removed and washed, and prepared for the
market in whatever form is required, the sulphureted hydrogen gas
being led to a holder and stored, as before stated.

The decomposition of the ammonium chloride by means of "alkali waste"
is carried out in a specially designed still. This is a tower 45 ft.
high by 8 ft. diameter, divided by horizontal plates into compartments
of about 3 ft. 8 in. in height. These compartments communicate with
one another by means of pockets, or recesses, in the shell of the
tower. A vertical shaft, with arms, revolves in the tower. The "waste"
is fed in at the top by means of hopper and screw feed. The liquor is