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1、Listening and Speaking (Students Book: p. 95)The aim of this experiment is to write a secret message with invisible ink.For the experiment, you need the following things: a lemon, a small container, a pen, some white writing paper, a candle and some matches.First, squeeze the lemon and pour the juic
2、e into a container. A glass or a cup will be fine.Next, take your pen and dip it into the lemon juice then write your message in large letters on a clean sheet of white writing paper.After that, blow on the paper to dry the lemon juice. Your secret message is ready and you can exchange messages with
3、 another student.Next, light a candle with the matches. Finally, hold the paper near the candle flame.The message will gradually appear on the paper. The words are a light brown colour.The message appears on the paper when you heat it because the lemon juice reacts with oxygen in the air. This reaction produces a brown coloured oxide which you can see.