How Much Salt Would I Need to Float in My Bathtub?

How to know if something floats in water? Easy, the density of the object should be less than that of the fluid.

In the case of the human body, the average density is 0.95 g/ml. The density of water varies with temperature. At 4.0° C (39.2° F), the density of water is 1 g/ml. It follows that the human body can float in water. That means any addition of salt that you then dissolve in water will make you float even better.

However, at room temperature, you need at least 100 grams of water to dissolve around 35 grams of salt. If the temperature changes, the amount of salt that water can dissolve also changes; increasing the temperature can help you dissolve more. But since we are planning to float in the salty water, reaching high temperatures is not really an option.

So basically, you cannot dilute more than 359 g of salt per one liter of pure water at room temperature. So, that would be your cap for maximum buoyancy with salt. After that, the salt will no longer dissolve. And although heating the water allows more salt to dissolve, thermal expansion causes the density to drop, so you shouldn’t even bother trying.

So, if your tub holds 200 L, you can add about 70 kg of salt, if you want to exaggerate. Although it may not be advisable to stay in for too long.

What is the most salty body of water on the planet?

The seas, oceans, and some lakes usually have a concentration of plus minus 35 grams of salt per liter of water. This salinity level is produced mainly because the rivers carry water with sediment that contains salt from the mountains. In the process, a small amount of water evaporates but most of it reaches the seas, oceans and lakes.

However, water salinity is not equally stable in all types of water bodies. It often varies by location and season, particularly in hypersaline lakes located in arid areas.

The saltiest water body on Earth is Gaet’ale Pond in Ethiopia. It is a small hypersaline lake located near the Dallol crater in the Danakil Depression. It is located over a hot spring of tectonic origin and has no apparent inlet or outlet streams. The water of Gaet’ale Pond has a salinity of 433 g per liter of water. Surprisingly enough, the Dead Sea is only the 7th most salty body of water on the planet. As of 2011, it had a salinity of 342 g per liter of water, or 34.2% (in 2011).


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