Deeper Into Jeopardy! XIII: An Eco-Category – $800

Jeopardy! category: AN ECO-CATEGORY (10-04-2014)

$800 clue: If your garden soil lacks magnesium, a green way to add it is to use magnesium sulfate, aka this salt named for a British town

Correct response

The gist: You might have had experiences with magnesium sulfate if you’ve had the opportunity to undergo flotation therapy. There, as when sold as a bath salt, the chemical with the formula MgSO4,commonly known as Epsom salt for the small Surrey town where the spring from which it was originally harvested is found, it’s used to balance the specific gravity of the water so that you feel more like you’re floating on nothing than floating in water. We can also thank Epsom salt for another aquatic treat – whale song. Magnesium sulfate is the primary compound in seawater that results in the high frequency noises quickly attenuating while low frequencies, like those made by whales, transmit smoothly. The magnesium sulfate (and to a lesser extent, boric acid) in the water absorbs high frequencies easily, converting the vibrations into thermal energy, while low frequencies are not as easily absorbed and as such can continue on transmitting for miles, with few higher frequencies to interfere.

On dry land, Epsom salts have uses too – like the clue says, they’re a good source of magnesium for plants, the element found in the centre of the chlorophyll, which is the molecule that lets plants absorb sunlight to create energy through photosynthesis. Essentially, then, that magnesium is what lets plants provide nearly all natural energy to Earth’s ecosystems. Pretty important.

Anhydrous Epsom salt in a Petri dish

The clue: There are really three ways to get to the correct response for this clue. The first and most straightforward is to simply know your gardening – what would you give plants that need magnesium? The second is through the chemistry – either knowing that Epsom salt is magnesium sulfate (since the writers helpfully supply that information), or at least that it involves magnesium which could help you make the jump to Epsom. Finally, you might know its history, and get it from the bit about the town. While I don’t know how many salts are named for British towns, I bet Epsom salt is really the only important one.

In Jeopardy!: I would have thought it would be more common, but “Epsom salt” only shows up in a measly four clues. Three of the four mention the fact that it’s named for a place in Britain; the fourth just wants its colour. Just searching “Epsom” brings up another six, all of which are about horse racing, as the Epsom Derby is one of the events in the English Triple Crown.

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