Saturday, 29 September 2012

Worse things happen at sea





If there's one thing the Indian Ocean trade proves - and to a lessor extent their Atlantic explorations - it's that Carthaginian and Roman traders were capable of trans-ocean voyages rather than the simple coast hugging ancient mariners are generally accused of. Staying at sea for extended periods brings all sorts of issues for the sailor, but the most important is generally the lack of drinking water. This was to curse the voyages of discovery during the middle ages and has meant the end for more than a few modern mariners. Yet, back in 78AD Pliny writes of two desalination techniques used at sea, one of which has only been recently re-invented. The first is pretty simple and probably dates to the earliest bronze age sailors...woollen fleeces were scattered about on the ship's deck to collect sea spray - Pliny says that ringing these out produced fresh water...although I'd imagine it still had a fairly high salt content. The other is considerably more sophisticated. Osmosis - the passage of water molecules though a semi-permeable membrane - was first demonstrated in 1748 by Jean-Antoine Nollet, yet Pliny explains that Roman sailors were using the process back in the 1st-century AD. He describes hollow balls or sealed clay containers being lowered into the water and trailing behind the ships - after a period of time these vessels were brought aboard filled with fresh water - something pretty remarkable since even to this day people are still dying of thirst in boats when, as the Romans knew, they are surrounded by water.

Find out if Calvus ever drank too much sea water