What it does
Salt water, milk and muddy water are all “something mixed into water”, yet they behave very differently. The difference is the size of the particles. This tool lets you test a mixture the way a school lab would.
Pick a mixture and the torch shines a beam through the beaker. In a true solution such as salt water the beam’s path cannot be seen at all. In a colloid such as milk, starch solution or fog the path lights up, because the particles are just big enough to scatter light sideways: the Tyndall effect. In a suspension such as muddy water the liquid is cloudy and little light reaches the screen. Leave to stand shows which ones settle, and Filter it shows which leave something on the filter paper. Drag the particle size slider to move smoothly from one kind to the next.
It follows the school topics on mixtures: solutes, solvents and concentration (Class 8 Science, solutes, solvents and solutions) and true solutions, colloids and suspensions, the Tyndall effect and the types of colloid (Class 9 Science, exploring mixtures and their separation). Separate real mixtures step by step in separation lab, and see why scattering makes the sky blue in Sky colour.
How to use it
- Choose a Level. Class 9 adds the colloid’s dispersed phase, dispersion medium and type (sol, emulsion, aerosol and so on) and the size boundaries.
- Pick a Mixture, or move the Particle size slider to try any size; the arrow on the scale under the beaker shows where it sits.
- Torch off and Torch on switch the beam. Leave to stand waits a while; Filter it pours it through filter paper. The text under the pill says what you would see.
- In Make a solution, set the grams of salt or sugar and of water to get the mass percentage.
Worked example
Pick Milk with water (particles about 400 nm, a typical rounded value). The pill says A colloid: the beam shows, nothing settles and everything passes through filter paper. Its dispersed phase is a liquid (fat drops) in a liquid medium: an emulsion.
Switch to Salt in water (about 0.3 nm): a true solution. No beam, no settling, nothing on the filter. Then Muddy water (about 20 µm): a suspension, cloudy, it settles, and filtering leaves the mud behind.
In Make a solution, 20 g of salt in 180 g of water makes 200 g of solution: 20 ÷ 200 × 100 = 10 % by mass.
Tips
- A colloid can look perfectly clear and still be a colloid. The torch test tells you.
- Filter paper cannot separate a colloid; a centrifuge or special membranes can.
- The size limits are rough. Nature does not switch sharply at exactly 1 nm or 1000 nm.
FAQ
Why can I not see the beam in clean air or salt water? You only see light that reaches your eye. In a true solution almost nothing sends the light sideways, so from the side the beam is invisible.
Is milk a solution? No. It is an emulsion, a colloid of fat drops in water, which is why it is white and shows the Tyndall effect.
Is anything stored? No. The questions are made fresh in your browser and nothing is saved or sent.
Where the numbers come from
- True solutions (particles below about 1 nm), colloids (about 1 to 1000 nm) and suspensions (above about 1000 nm), the Tyndall effect, dispersed phase and dispersion medium, mass by mass and mass by volume percentage: standard school chemistry found in any textbook. The size boundaries are the usual rounded school values.
- The particle sizes of the example mixtures are typical, rounded teaching values: real samples vary widely. The beam brightness is a picture, not a measurement. Percentages were checked by hand (20 g in 180 g of water = 10 %).
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.