My friend Paul will never forget his chemical teacher. He was a little man with thick glasses, and he had a strange way of making his classes live and interesting. And his lessons were not easily forgotten. Paul remembers one of his first lesson from his teacher. After all the students were in a chemistry lab, the teacher brought out three bottles. One was full with petrol, one with castor oil and one with vinegar."Now watch carefully," said the teacher. He filled a cup with some the petrol, some of the castor oil and some of the vinegar. As the students watched him, he mixes the three together. After that, he held up one of his fingers and showed to the class. He then dipped it into the cup and said" You must do everything as I do it."