808

SODA. —Black-ash Furnaces and Boiling-down Pans.

ting boat pans. The bottom is purposely sot on a salt may quickly accumulate in it and bo “fished” out.brick-wall, and not touched by the fires, so that the The fished salt is much purer than the “drainer

Fig. 17.

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Fig. 18.

salt” of open pans, as will be seen hereafter, and theresidue is worked up either into caustic soda or into“ caustic ash.”

Fig. 19.

0_I i o 9 12 FEET

Sometimes the ball-furnace fire first travels overan open pan and then under a boat pan ; or, morefrequently, under two boat pans in succession.Those boat pans used in connection with ball-fur-naces are sometimes made of cast iron, sometimes ofwrought iron. The pan furthest from the furnace

Fig. 20.

is placed about 6 inches higher than that nearer thefurnace, and the bottom of the latter corresponds inheight with the summit of the black-ash furnace arch.One continuous 14-inch wall, on which the bottomof the pan rests, sustains the principal portion ofthe weight of the latter; while two other 14-inchwalls at the front and back (forming continuationsof the former wall), built up to the flanged tops ofthe pans, support their two sides. These three

longitudinal walls form between them two fluesthrough which the black-ash furnace fire passes.In order to force the fire nearer to the pans several

Fig. 21.

9

wmm,

m

■iia

bridges are built up within 8 or 12 inches of thesides of the pans, following their sweep, the space