Mechanical separation

You know that rice is panned to remove the sand mixed into it. Six methods of the same kind, each with the property it depends on.

Mechanical method	Where it is used	The physical property it uses
Winnowing	Removing chaff from rice	The density difference between the components
Sieving	Removing gravel from sand	The difference in the size of the component particles
Panning	Removing grit from rice	The density difference between the components
Floating in water	Removing bad eggs from a batch	The density difference between a component and water
Sluicing	Separating gold from ore-bearing earth	The density difference between the components
Magnetic separation	Separating certain minerals from mineral sands	The magnetic property of a component

What they have in common

Separating the components of a mixture with the help of physical properties such as the density of the components, the size of the particles, the shape of the particles, and their magnetic and electrical properties, is called mechanical separation.

Reading the third column

Three of the six rows say density and one says particle size. That is not a coincidence — these are the two properties that are easiest to exploit without any apparatus at all, which is why these methods are old, cheap and still in daily use in kitchens and on farms.

Nothing chemical happens

Every method in this table leaves both components exactly as they were. That is what makes it a separation of a mixture rather than a reaction, and it is the same point the very first skill of this chapter made about filtering copper sulphate out of naphthalene.