Barney and Tim are finding out what happens when certain substances are mixed together.
They are interested in OBSERVING any changes and trying to find out whether the change is permanent (IRREVERSIBLE) or temporary (REVERSIBLE).
They start by drawing up a chart to write their results in:
|Sand||Water||Did not dissolve||Reversible|
|Sugar||Water||Dissolved - clear|
|Instant coffee||Water||Dissolved - brown||Irreversible|
|Andrews salts||Water||Fizzed - gas produced||Irreversible|
|Bicarb of soda||Water||Did not dissolve||Reversible|
|Bicarb of soda||Vinegar||Fizzed - gas produced||Irreversible|
|Boiled sweet||Water||Dissolved - pink||Reversible|
|Dirty 2p coin||Lemon juice||Coin clean/juice dirty||Irreversible|