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LIN SHU-YEN
LW
PSS
LEW
GL
FB
Figure 3. Cross-section of the leaching vat. EW, earthern wall of the vat; FB, filtered concentrated brine; GL, ground-level; LW, level of sea-water in the vat; PSS, prepared salty soil; T, coarse twigs, the lower layers arranged obliquely, the upper ones transversely over the canal at the bottom of the vat.
The filtered brine is collected into the bottom shallow canal and is drawn off into the two brine-storage tanks (figure 1, S), which are each about 4 feet in diameter and 3 to 5 feet in depth. Immediately in front of these storage tanks are the drying or crystallization ponds, six to ten in number. They are constructed in a row and separated by low ridges of mud.
by low ridges of mud. The bottom of the pond is set with a layer of small roundish pebbles over which a heavy stone-roller is pulled to make it hard. Two canals, one lower and the other higher than the bottom level of the drying ponds, are constructed along the edges of the ponds. The higher canal (figure 1, HC) serves to lead the brine bailed from the storage tanks into the drying ponds whilst the lower (figure 1, LC) is to lead the brine back to the tanks,
Brine can be conveyed from the storage tanks to the drying ponds to evaporate to dryness at any time when the weather is fine and the sun is strong. The evaporation process takes about 8 to 10 hours. When the brine is not strong enough to ensure crystallization of salt within a day, or if rain falls before crystallization takes place, the brine can be run back to the storage tanks.