Water put on No. 5.
No. 5 pumped upon No. 2 (No. 5 sludge thrown away).
The black ash is treated thus:—
No. 4, full of black ash, is wet down with Nos. 1, 2, and 3, and pumped up to the causticising-tank.
Water is pumped out to Nos. 2 and 3, and then drained upon No. 4, the liquor still being pumped up from No. 4 while the water is being pumped upon Nos. 2 and 3, which are kept full. This is continued until the liquor tests only 2° to 1° B.
No. 4 is now drained upon No. 1.
No. 3 pumped upon No. 4, and this drained into No. 1 (now full).
No. 3 pumped upon No. 5.
Water pumped upon No. 2 (No. 2 the next to be thrown away).
No. 5 is by this time full of fresh black ash, and the same process is carried out with No. 4.