How Much Oxygen in the Air?

Air is composed approximately of one-fifth oxygen and four-fifths nitrogen, with traces of a few other gases. Experiments with convection currents prove that a flame must have a constant supply of air if it is to remain alight. With this knowledge, you can find out how much oxygen there is in a milk bottle full of air.

Fill a dish with water, light a stub of candle and carefully float it in the dish. When the flame has established itself and is burning steadily, cover it with the upturned milk bottle.

The candle will continue to burn for a few seconds because it has a small supply of oxygen available in the air now trapped inside the bottle. However, the flame will use this oxygen quite quickly and will then be extinguished. At the same time, because the oxygen content of the bottle has been used, an area of low pressure will result. The outer air, pressing down upon the surface of the water in the dish in its endeavor to enter, will instead, force water up into the bottle, thus indicating the amount of the oxygen which has been used.

Children learn best through doing

Before children can understand a thing, they need experience: seeing, touching, hearing, tasting, smelling; choosing, arranging, putting things together, taking things apart. Experimenting with real things.

Old-time school teaching used only words and the teachers thought children knew something if they could repeat it. Now we know better. To reach practical understanding we do not need to use many words with young children.

Children are clever. They learn a lot, without being taught. The greatest skill - to be able to talk, to communicate is learnt outside school. In the classroom it's the children who need to talk the most. Unfortunately it is the teacher who does most of the talking!