So here's the setup:

We're talking about salt again. Specifically, we're talking about how salt was made here, locally, in the 19th century. We already talked about why people were so invested in making it, and how the design evolved. But today we're going to talk about the nitty gritty—how the water got into the rooms, why there were three of them, and what they each produced—not just sea salt! 

Both physically and chemically, the process is a bit more complicated than I'd imagined. First of all, there are three rooms—basically walled wooden platforms. As you see up there, water is pumped into the first room, called the water room or the slime room, by a canvas and wood windmill. This nickname "slime room" came from the fact that all sorts of sea life was pumped in—there was no filter—instead, the water was left in this room to settle. Once the debris was comfortably settled the saltmakers would pull a plug, and the water would flow via gravity through a hollowed out pine log into the second room. Here a lot of interesting things happened.

This room was called the pickle room, or the brine room. In warm weather, this is where evaporation would start, and calcium salts like lime and gypsum would precipitate out of the water. When the saltmakers noticed the first edible sea salt crystals starting to form (sodium chloride), they would pull the plug and let the thick, sludgy brine flow again via gravity and through a hollowed out pine log into the third room. This is where the final evaporation took place, and about three weeks from when the water entered the first room, crystals of very dry sea salt were raked up, put into barrels, and moved to a warehouse for storage.

But in cold weather, something different happened. Seawater is full of chemical elements: magnesium, sulfur, calcium, chlorine, etc. Depending on temperature and conditions, these elements react differently and come together to form different bonds. What might give you lime and gypsum and sea salt on a warm day gives you something else completely on a cool day.

That's where Glauber's salts come in. In cold weather as the seawater started to evaporate, a form of sodium sulfate formed in the brine room—called Glauber's salt for the Dutch chemist who discovered it in 1625. Initially this frustrated saltmakers, because what they wanted was edible sea salt to preserve cod. But they quickly realized they could sell Glauber's salt to industrial producers—it was used to make washing soda for detergents, tanning leather, and dying cloth. What's more, the cold brine leftover from harvesting Glauber's salts could be used to make Epsom salt, or magnesium sulfate. People used these for medicinal purposes—they put them in baths to relax or sooth muscle aches or reduce stress—any number of things. 

I had no idea salt could be so complicated! But it's pretty cool to see how Cape Codders turned what seemed initially like kind of a bummer into a winter enterprise. If you check out the production stats from last week, you'll see that in 1837 for example, Dennis produced 500 barrels of Epsom salts. Pretty cool!

All you modern day saltmakers...have you run into any issues of different chemical combinations precipitating out in cold weather? Or have you been able to avoid that with the greenhouse setup or another method? I'd love to hear.

P.S. A very interesting document from the Woods Hole Historical Collection on saltmaking in the 19th century.


Unknown said...

thanks for such a fun blog. Provincetown Center for Coastal Studies suggested i look you up. i'm interested in learning sea salt production at a hobby level. any chance you have tips to share?

Elspeth said...

hi melissa,

thanks so much for getting in touch. i personally don't have much experience with making sea salt (i've done it once or twice), but you should talk with tamar haspel of starving off the land (http://starvingofftheland.com/). she makes it at home on her woodstove all the time. good luck!

all the best,

wypo┼╝yczalnia samochod├│w warszawa said...

interesting idea, as you come out this recipe please :) good luck...

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