[chris (OP)]

If I wanted to recreate the buoyant effect of the Dead Sea so that I could float about in my bath, how much salt would I need to add?

Chris

[Don_1]

In such a small body of water, I doubt it would be possible to recreate the buoyancy of the Dead Sea.

[rosalind dna]

Chris I doubt that you would be able to recreate the Dead Sea in your bath because you'd need more salt than you'd be able to purchase.

As the Dead Sea's millions of years old I think.

Also the salt would remove the enamel or chrome for your bath and probably damage the taps for ever.

[graham.d]

I can't see the difficulty. You just get to a similar level of salinity by dissolving salt. It's about 10x the salinity of ordinary sea-water. It's not at all impossible to do this, though there is a question of why you would want to. 340 grams/litre is what you would need.

The Dead sea's salt content is not primarily sodium chloride, but for the purposes of this theoretical question I don't think that is so important.

[Don_1]

Graham, chris want's to recreate the buoyant effect of the Dead Sea, your saline solution will only recreate the salinity, not bouancy.

[JP]

Archimedes' principle says that a floating object will displace a weight of water equal to its own weight.  Unless I'm missing something, you should be able to increase the buoyancy of the water by increasing its density, and adding salt would let you do that.

[Bored chemist]

Graham, chris want's to recreate the buoyant effect of the Dead Sea, your saline solution will only recreate the salinity, not bouancy.

Why do you think the dead sea is so bouyant?

Anyway, you could look up the minerals in the dead sea water (largely magnesium and sodium chlorides I think) and mix up a similar brew in the bath.
It wouldn't be absurdly expensive. You would need roughly 120g of MgCl2 for each lire of bath water. You can pick that up on ebay at about £20 for 5Kg. You would also need about as much again of a mix of NaCl and KCl and you can get close enough to that from the supermarket as low sodium salt substitute.

[Don_1]

Graham, chris want's to recreate the buoyant effect of the Dead Sea, your saline solution will only recreate the salinity, not bouancy.

Why do you think the dead sea is so bouyant?

Yes, but with such a small body of water, it would not be possible for chris to float in his bath, unless it's a real big bath, because, as jpetruccelli has pointed out, 'Archimedes' principle says that a floating object will displace a weight of water equal to its own weight.' so I doubt there would be the capacity in a bath to get sufficient water in it for a human to float. Would there? Oh! I don't know though, I could be wrong.

[Chemistry4me]

How much salt do you need to get an egg to float in a half filled glass of water?

[rosalind dna]

How much salt do you need to get an egg to float in a half filled glass of water?

Hardly any and if the egg has gone off then it'll sink even in salty water.
Of course it depends on the size of the glass or tumbler.

[_Stefan_]

Fresh eggs will sink in fresh water; stale eggs will float.

[Fortran]

If your bath is downstairs and on solid foundations you could recreated the dead sea bouyancy by filling it with mercury. If not try custard or sugar syrup.

[lyner]

How much upthrust should a saturated salt solution give you?
The solubility of NaCl is about 36g/100ml at 25 Celcius (for a saturated solution; you won't get any more than that to dissolve).
That would give a relative density of 1.36 for your bathwater, providing 0.36kg upthrust for each kg displaced.. You would float with about 1/4 of your body out of the water. That would be pretty impressive and worth a go.
You don't need a particularly large amount of water for you to float. You only need to 'displace' you own weight of the stuff - it doesn't actually have to be there in the first place. If you fit tightly into your bath - I do in mine - you would not need much extra volume to bring the level up to your chest* once you were in there.
Using rocksalt for roads would mean it needn't cost a lot. Bearing in mind that the water needn't be very deep (about the same as a normal bath)  because you should be floating (!) with your bum just above the bottom of the bath .
Actually doing it in your bathroom wouldn't be a good idea, tho.
A good bathfull is about 200l, so that will need 72kg of salt to get the required density.  If you used a round bottomed container - say a moulded fishpond- it would be a better shape with less 'wasted' water around the edges.

* I remember being told, on a visit to a lighthouse as a kid, that the rotating shutter was floating in a circular channel of mercury to provide a low friction bearing (the mechanism would have been a tiny motor, even clockwork- I don't remember). Very little mercury was actually needed because the circular channel was only just wider than the revolving cylinder.