i will never forget my first chemistry teacher. he was a little man with thick glasses, but he had a strange way of making his classes lively and interesting. and his lessons were not easily forgotten.i still remember one of my lessons from this teacher. after the students were all in the lab, the teacher brought out three bott[es. one was filled with petrol, one with castor oil and one with vinegar. "now watch carefully," said the teacher.

　　he then filled a cup with some of the petrol, some of the castor oil and some of the vinegar. as the students watched him quiet[y, he mixed the three together. after that, he held up one of his fingers and showed it to the class. he then dipped it into the cup. after a few seconds he took his finger out. "now watch," he said. "remember, you must do every thing as i do."he put a finger in his mouth, tasted it and smiled, looking rather pleased. then he handed the cup around the class of students. each student dipped a finger into the mixture and sucked it. instead of smiling, each of them made a face. the mixture tasted terrible.

　　when the cup was at last returned to the teacher, he said sadly, "i` m sorry, none of you watched carefully enough. yes, i sucked a finger, but the finger i put into my muth was not the one i had dipped into the cup."it was my first important lesson as a student of chemistry and i never forgot it.