Consider a mixture of fine sand and water, freshly shaken Consider a mixture of fine sand and water, freshly shaken. The fine sand is not dissolved in the water; it is just floating around – temporarily suspended in it. Certainly one way to separate this mixture would be to have it just sit undisturbed and allow gravity to pull the more dense sand particles down to the bottom. This is known as sedimentation. The substance that settles out to the bottom is referred to as the “sediment” or “precipitate.” (just as rain or snow that falls to the ground is sometimes referred to as “precipitation”). The liquid left on top is called the “supernate.” This process may be fast if the sediment particles are big enough or the density difference is great enough, or it may take hours or even days for very small sediment particles or for mixtures in which the two components are very close in their densities… or for mixtures involving very viscous liquids! But there is a way to speed up gravity a bit! SEDIMENTATION = water = sand

A centrifuge is a device that spins mixtures around very quickly. As the mixture spins around, it creates a tremendous “G-force” – sometimes several thousand times stronger than normal Earth gravity. Thus, substances that would take hours to separate by sedimentation can be separated in just a few seconds! CENTRIFUGATION

A centrifuge is a device that spins mixtures around very quickly. As the mixture spins around, it creates a tremendous “G-force” – sometimes several thousand times stronger than normal Earth gravity. Thus substances that would take hours to separate by sedimentation can be separated in just a few seconds! CENTRIFUGATION

Of course, another method for separating out a mixture of a fine powder dispersed in a liquid would be by filtration. Here the particles are really being separated by their size: The smaller particles (the water molecules) can easily pass through the small holes in the filter paper. The larger particles of sand cannot and so they get trapped in the filter. The substance that gets trapped in the filter is called the residue. And the substance (liquid) that passes through the filter is often refered to as the “filtrate.” FILTRATION It is important to keep in mind that with mixtures like salt water or sugar water, the dispersed particles are so small that they would never settle out, even if given hundreds of years! There are some filters, however, know as “semi-permeable membranes” that are capable of filtering such small particles out of water.