The density road · pan by pan · one season
Twenty-three and a half degrees, walked one pan at a time
Brine does not move down this works by pump. It moves by weir: each pan sits a little lower than the one before it, and when the reading at the far wall reaches the figure in the table below, a board is lifted and the pan walks on. The whole road is 26 hectares of standing water and one sluice, and it runs on sun and wind alone.
The reason there are nine pans and not one is that seawater is not only salt. Every mineral in it has a density at which it gives up, and they do not give up together — carbonate at about 7, gypsum between 14 and 16, sodium chloride at 25.7. Each pan exists to take one of them out before the next pan is allowed to fall.
The pans, in order
| Pan | In at | Out at | Area | Depth | Falls out here |
|---|---|---|---|---|---|
| Reservoir | 3.5 | 3.5 | 9,400 m² | 1.8 m | Nothing — it is the control |
| Condenser 1 | 3.5 | 5.2 | 34,000 m² | 40 cm | Silt, weed, the last of the estuary |
| Condenser 2 | 5.2 | 7.0 | 27,000 m² | 28 cm | Calcium carbonate |
| Pan 3 | 7.0 | 12.4 | 12,600 m² | 25 cm | Nothing — it is only water leaving |
| Pan 4 | 12.4 | 16.0 | 9,400 m² | 25 cm | Gypsum, in clear needles |
| Pan 5 | 16.0 | 25.7 | 7,800 m² | 22 cm | The last gypsum; the pan turns red |
| Crystallisers 6a—6f | 25.7 | 27.0 | 4,200 m² | 20 cm | Sodium chloride — the salt |
| Bittern tank | 27.0 | 29.5 | 12,000 L | — | Magnesium and potassium salts |
61,000 m² of condensers against 4,200 m² of crystallisers. That ratio is not a preference — it is what evaporation requires to put 39 tonnes of seawater through the works for every tonne of salt that leaves it.
The works, drawn to area
The plan is drawn to the pans' relative areas and scrolls sideways.
How the season runs
| Stage | Dates | Note |
|---|---|---|
| Flooding | late April | reservoir first, then condensers 1 and 2 |
| First walk-on | late May | condenser 2 to pan 3, at 7.0 °Bé |
| Crystallisers filled | first week of July | 6a and 6b, 20 cm, from pan 5 at 25.7 |
| First rake | second week of July | nine to fourteen days after filling |
| Pan walks | Thursdays, 14:00, May to September | twelve people, £8, flat ground, no shade |
| Last rake | September, weather deciding | whenever rain puts a crystalliser back to 24 |
| Sweep | October | floors scraped, banks re-puddled, works closed |
Everything on this page is measured at 07:00 with a glass hydrometer, pan by pan, and written on a board in the sluice house before it is written anywhere else.
Next: the four grades and what each is for.
Order salt