More information about the work of Robert Brown may be found in suitable reference texts, a CD-ROM such as Encarta, or Encarta Online.

Computer simulation of the arrangement and movement of particles in the three states of matter provides another useful teaching aid to this topic. The States of Matter CD-ROM from New Media is a useful means of illustrating particle theory in the classroom.

A variety of materials can be used to observe Brownian motion. The fat droplets in milk demonstrate this type of movement as they are bombarded by the water molecules in which they are suspended. It is also possible to use talcum powder dispersed in water.

Brownian motion can be observed in the cells of some aquatic algae.

Diffusion

The demonstrations of diffusion shown in this programme could be supplemented with everyday examples of the same phenomenon. Releasing a small volume of deodorant from an aerosol can provides a simple classroom demonstration of gaseous diffusion. The diffusion of tea from tea bags placed in a large beaker of boiled water is a familiar example of diffusion in liquids. There are many more examples of diffusion at home.

The relationship between the rate of diffusion of a gas and its molecular mass is given by Graham's Law.

Changes of State

Students could gain some direct experience of the energy transfers which take place during evaporation by blowing across a small quantity of water or ethanol dabbed on the back of the hand. This work could be extended in the laboratory by plotting a cooling curve for a substance such as stearic acid. Why does the temperature not change at the melting and freezing points of the substance even though

an energy transfer accompanies the change of state?