A heterogeneous mixture composed of tiny particles suspended in another material. The particles are larger than molecules but less than 1 Ám in diameter. Particles this small do not settle out and pass right through filter paper. Milk is an example of a colloid. The particles can be solid, tiny droplets of liquid, or tiny bubbles of gas; the suspending medium can be a solid, liquid, or gas. Note: a gas mixed with another gas is not a colloid.