Drop a few pieces of solid colouring matter, (analine blue, blueing, or potassium permanganate) into a beaker of cold water. Place the beaker over a heater and observe the coloured portion rise.
Wet sawdust will make a good substitute for the colouring matter. A sealing jar or even a tin cup will do instead of the beaker. The stove or a dish of hot water will take the place of the lamp.
PROBLEMS
1. Using a thermometer, see whether the water at the bottom is warmer than that at the top while the beaker is being heated.
2. Heat some oil and pour it over the surface of some cold water. Lower a thermometer into this. Does the water at the bottom soon become warm?
3. If your kitchen is provided with a hot-water tank, find out what part of the tank first becomes warm after the fire is lighted.
4. In bathing, where do you find the coldest water of a pond or still river? See Science of Common Life, Chapter VI; also The Ontario High School Physics, page 280.
CONVECTION IN GASES
A good apparatus may be made by cutting two holes one inch in diameter in one side of a chalk box, replace the lid with a piece of glass, place a lamp chimney over each hole and a lighted candle under one of the chimneys. Hold a piece of smoking touch-paper at each chimney in turn and note direction of air current.