DYEING AND CALICO PRINTING.

114

so-called coke-towers. These towers are stone built, the stone being of akind not ailed upon by hydrochloric acid, cemented with coal-tar and fire-clay.The dimensions of the towers vary between 36 and 42 feet for the height, and4 to 5J feet internal width. A wall divides the tower nearly throughout itslength into two compartments, the dividing wall being carried to within ashort distance of the top of the building. The two compartments are filledwith pieces of coke resting on a perforated stone floor, and over the surface ofthe coke, from the top of the tower, water is caused constantly to trickle.The gas from the decomposed salt is condudted by stoneware tubes to thesetowers, and is there condensed, so that only a fraction of a per cent escapesinto the chimney stalk, with which the second compartment of the coke-tower is connedled.

The furnace in which the salt is decomposed consists of two muffles. Oneof the muffles is of fire-brick, and encloses a space of 30 feet in length by9 feet in width, vaulted and so provided with flues that the flames may havecomplete circulation. The other muffle is of cast-iron, the interior forming asegment of a circle of g feet diameter, and 1 foot g inches in depth. A lid, alsoof iron, is provided with two openings, one of which communicates withthe second muffle, while the other serves for the introdudtion of the salt.Half a ton of common salt having been introduced into this muffle, sufficientsulphuric acid (17 sp. gr.) is added to form a neutral sulphate. g5 parts ofacid of 17 sp. gr., or 104 parts of an acid at 1-62 sp. gr., are required to com-pletely decompose 100 parts of salt. When the mixture of acid and salt isdry it is raked over into the second muffle, kept at a bright red-heat to expelthe hydrochloric acid gas. Many large firms in this manner decompose 500 tonsof common salt per week.

2. The next part of the process consists in the conversion of the sulphateinto crude soda; and this is effedted by submitting a mixture of—

Sulphate. 100 parts.

Chalk. 100 „

Slaked lime . 50 ,,

to fusion in a reverberatory furnace. Another mixture of—

Sulphate. 100 parts.

Chalk.go to 121 ,,

Small coal.40 to 75 „

is preferred in some works. The furnace employed is generally a ballingfurnace, shown in Fig. 12. Mr. Wright has found that the loss of soda amountsduring this process to 20 per cent of the sodium contained in the sulphate, as

in the following proportions —

Undecomposed sulphate.3-49

Insoluble sodium compounds.5-44

By volatilisation. 1-14

In the waste .361

During evaporation of the liquors .. .. 6-56

20-24

The composition of the crude or ball soda may be represented by thefollowing percentical analysis :—