The gases from a large limekiln supply the dilute carbonic acid gas, which contains 25 per cent. to 30 per cent. of pure gas, the principal diluting gas being, of course, nitrogen.  This kiln gas is drawn from the kiln by a blowing engine, and is first cooled in two large receivers.  It is then forced into the solution of sodium carbonate in the absorption tower, 65 ft. high by 6 ft. diameter, filled with the liquor.  The tower has many diaphragms and perforated “mushrooms,” to cause a proper dispersion of the gases as they ascend through the liquor.  The strength of liquor found best adapted for the work is equal to a density of about 30 deg.  Twaddell.  After saturation the mud of bicarbonate of sodium is drawn off and passed into the “decomposer,” a 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 deg.  Fahr. to 58 deg.  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 heated by steam blown in to over 212 deg.  Fahr.  The ammonium sulphide is led direct into an absorbing vessel full of brine.

It now only remains to see how it is proposed to deal with the sulphureted hydrogen gas which represents the sulphur recovered from the waste.  It can be burnt direct to sulphurous acid and utilized for the production of vitriol perfectly pure and free from arsenic, commanding a special price.  But Messrs. Parnell & Simpson state that by a method of restricted combustion they are able to obtain nearly all the sulphur as such, and put it on the market on equal terms with the best Sicilian sulphur.  We did not gather that this has yet been done on the working scale, however.