For an object to float in liquid, it must weigh less than the liquid it seeks to displace. What this means is that the heavier or denser the liquid is, the more likely an object will float in it.
Therefore, adding salt to water makes the latter denser, hence increasing its weight and volume.
So, yes; potatoes float in saltwater; but only if the density of the saltwater is higher than that of the potato.
In a nutshell, floating is all about buoyancy and how much liquid an object immersed in water displaces.
If the fluid surrounding the object is denser and more voluminous than the object, the latter will float. The act of adding salt to water makes it heavier, which means a potato immersed in it is likely to float.
Table of Contents 
- Explaining the Archimedes Principle of Buoyancy
- Why Salt Makes Objects Float
- Potato Floating Experiment
- The Dead Sea Experiment
- Types of Potatoes
- Various Potato Uses
- 1. Starchy Potatoes
- 2. Waxy Potatoes
- 3. All-Purpose Potatoes
- Different Varieties of Potatoes
- 1. The Russet Potato
- 2. New Potatoes
- 3. Yukon Gold Potatoes
- 4. Kennebec Potatoes
- 5. The All Blue Potato
Explaining the Archimedes Principle of Buoyancy
According to the Archimedes Principle of buoyancy, "when a body is immersed in a liquid, it experiences an upward buoyant force (or thrust), which is equal to the weight of the liquid displaced by the body".
Buoyancy makes some objects float, while others don't.
Simply defined, buoyancy is an upward force exerted by a liquid on an object. If you drop an item in liquid, it's pulled down by the force of gravity.
The extent or the magnitude of the force is directly proportional to the mass or weight of the object.
As the liquid pushes an object back up, the extent or magnitude of the force depends on the volume or weight of the displaced fluid.
If the object weighs less than the displaced fluid, it floats. Therefore, buoyancy is directly influenced by an object's density and that of the liquid.
To explain the impact of mass and volume on the chances of an object floating, take the example of a steel ball.
When inserted into water, it will definitely sink for the very reason that it fails to displace a proportionate weight of water.
However, if the same steel, but this time in a bowl-shaped form, is placed in the same water, it will float.
This is because its weight is now distributed over a larger area, meaning it displaces water that is equal to its weight.
This explains why large sea vessels with massive cargo are able to float on water.
Why Salt Makes Objects Float
When you add salt to the water, the physical forces exerted by water on objects change, which causes the objects to float.
The density of water increases as one adds salt to it. If you put salt into water, it dissolves.
The iron in it embeds itself into the spaces between the water molecules.
The saltwater's mass is higher and its volume just fractionally greater, making it denser than freshwater.
What this means is that the magnitude of buoyancy is proportionally higher in salt water than in freshwater for the same volume of water upon displacement by an object.
Potato Floating Experiment
Cut a piece of potato into two equal pieces and insert them each in a bowl: one containing fresh water and the other containing normal tap water.
After half an hour, you will notice that the potato inside the saltwater will have shrunk while the one (the control experiment) will have swollen slightly.
The explanation for this is simple. The potato left in saltwater shrinks because water is diffused from it (a less concentrated solution), to the more concentrated solution surrounding the potato, causing it to shrink.
On the other hand, the potato left in tap water is taking in water, causing it to swell.
This is because the solution inside the potato is more concentrated than that of the tap water surrounding it, meaning that water is diffused into the potato.
This simple experiment explains why a potato sinks in freshwater but floats in saltwater.
The answer, in the control experiment, is osmosis (tap water being absorbed by the potato), causing the potato to sink.
The other experiment is a sort of reverse osmosis (diffusion), which implies that water is moving out (diffusing) of the potato and into the saltwater, causing the potato to float since it has lost weight.
The Dead Sea Experiment
If there's one place to experience buoyancy in the world, that place is The Dead Sea in Israel. The sea is basically a dead end. Tucked at the end of the River Jordan, it's the lowest point on land.
Salt carried by the river into the sea becomes highly concentrated as evaporation kicks in. To give you a clear idea of how salty the dead sea is, it has 300 parts per thousand.
The ocean, by contrast, has only 35 parts for every thousand. This extremely high salinity explains why swimmers float easily in the Dead Sea, making it a popular tourist attraction, where people effortlessly recline on the water as they engage in their favorite reading pastime.
Types of Potatoes
There are about seven different types of potatoes. The categorization is based on their shape and color. Each of the potato types has numerous varieties. Below are the seven types of potatoes commonly found in the U.S:
Russet Potatoes: featuring pale flesh and rough brown skin, these potatoes are large.
Yellow potatoes: these have yellow flesh and thin gold skin.
White Potatoes: These have pale flesh and thin beige skin. They look more or less like tanned skin.
Red Potatoes: This potato type spots pale flesh and thin red skin.
Blue or Purple Potatoes: These potato types have matching purple flesh and blue or dark purple skin.
Fingerling Potatoes: These are so-called due to their tubular shape. They are also small and have various flesh and skin characteristics.
New Potatoes: These are harvested young (or before their maturity date). They are characterized by creamy flesh and delicate, thin skin, and a variety of colors. They are also known as baby potatoes.
Since the ability of potatoes to float in saltwater depends on their weight and mass, the above types of potatoes will have different floatation results since they feature different shapes, weights, and mass.
Various Potato Uses
Besides categorizing potatoes on the basis of their flesh and texture, another way to look at them is to identify how to prepare them. In terms of texture, there are three different classifications of potatoes:
1. Starchy Potatoes
These feature a dry, mealy flesh and a high starch content. Potatoes with a dry texture tend to break and crumble effortlessly, making them ideal for baking or mashing. Since dry flesh usually soaks up liquids, just like a sponge, if you add butter or a dairy product to your potato, it will absorb it evenly and quickly. Starchy potatoes are great for making french fries. As its exterior absorbs oil, it becomes finger-licking crispy while maintaining a fluffy interior.
2. Waxy Potatoes
The characteristics of a waxy potato include high moisture content, creamy flesh, and minimal starch. They are usually thin-skinned and you don't have to peel them before cooking. They don't fall apart like starchy potatoes upon cooking. They maintain their shape, making them perfect for simmering in stews, soups, baking in casseroles, or boiling for potato salads.
3. All-Purpose Potatoes
If you are looking for the best of all worlds, the all-purpose potato is it. They have some amount of starch that gives them a fluffy texture when baked or mashed. They also come with a similar level of water content, helping them to maintain their shape when pan-fried, simmered, or roasted. It's the best trade-off if you are looking for the best balance between waxy and starchy potatoes.
Different Varieties of Potatoes
Potato varieties in the world are in the thousands. However, those grown commercially in the U.S are not that many. They differ in texture, size, and skin type. Here's a list of five of the potato varieties (and their uses) you will find in the U.S.
1. The Russet Potato
You can easily recognize russet potatoes by their large size and dark brown, ruddy skin. These are great if you want to make baked potatoes. They are also great for mashing, but you will have to peel off the skin first. Since they are large and starchy, you can cut them into enough servings of french fries. Besides, they become crispy upon deep frying.
2. New Potatoes
These are not a real variety. "New" here implies that they are harvested while still young, irrespective of their variety. The ideal time to harvest them is just after flowering. They feature delicate, thin skin and creamy flesh. They are waxy and can be roasted with their skin on. Ideally, you should consume them soon after harvesting as they are not ideal for long-term storage.
3. Yukon Gold Potatoes
This is a highly popular all-purpose potato. It comes in a thin gold skin that you don't have to peel before mashing. It has a buttery, creamy flesh and sweet flavor. These are the types of potatoes you will find in commercial kitchens and restaurants.
4. Kennebec Potatoes
If you ask a competent chef in the U.S, they will swear by the fried Kennebec potato. Don't be surprised to see the name of this potato featured on the menu followed by a description extolling its qualities and highlights. The Kennebec contains the perfect balance of moisture and starchiness that gives it a nutty, crispy, golden-fried, unique flavor.
5. The All Blue Potato
Just like the Al Blue variety, Blue potatoes feature purple flesh and dark purple skin caused by the high concentration of an antioxidant known as anthocyanin. Since they are classified as all-purpose, All Blue potatoes are ideal for various cooking methods. If you are looking to make a delicious blue mash, get this variety as it has more starch content than the other blue potatoes. You can spot All Blues from a pile of other blue varieties by their distinct pale ring found in their purple flesh.
There are many potato varieties in the United States, and indeed around the world. When inserted in saltwater, each of these varieties will float. However, the volume and weight of a potato determine the level of displacement in saltwater.
Diffusion usually takes place from a solution with a lower concentration to one with a higher concentration.
The reverse, diffusion to a solution with a lower concentration is called osmosis. In the case of our potato, the one in saltwater loses water to the saltwater (diffusion), while the one in tap water gets more water (via osmosis), making it heavier and, therefore, more likely to sink.
Therefore, the reason potatoes in saltwater will float is because they are losing fluids to the salty water around them. As a result, they shrink and become lighter depending on how much water they’ve lost, causing them to float.