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The Development of Rubber
Here is the story of rubber. From the earliest time it was common knowledge _______(51) the Peruvians that when a cut was made in the outside skin of a rubber tree, a white liquid _______(52) milk came out, and that _______(53) this a sticky (粘的) mass of rubber might be made. This rubber is soft when warm, so that it is possible to give it any _______(54). The Peruvians made the_______(55) that it was very good for keeping out the wet. Then in the early 1800's, the Americans made use of it for the-first time. First they made overshoes to_______(56) their feet dry. Then came a certain Mr. Mackintosh, who made coats of cloth covered with natural rubber. From that day to this we have been coating cloth with rubber as Mr. Mackintosh _______(57), and our raincoats are still named after him.
But these first rubber overshoes and raincoats were all soft and sticky in summer, and_______(58) and inelastic (无弹性的) in the winter when it was cold. But the rubber we have today is soft and elastic (有弹性的),_______(59) very strong m even in the warmest summer and the coldest winter. This was made_______(60) by a man called Goodyear. After many_______(61), he found that nitric acid (硝酸) made the rubber much better, but it is not hard and strong enough. Then a strange thing took_______(62). A friend of his, Nicholas Hayward, had the idea in his sleep that rubber might be made hard and strong if mixed with sulfur (硫磺) and put in the sun. Goodyear put this idea_______(63) the test, and saw that it did have more or less the desired effect though somewhat less than more. The only effect it had was on the outside of the rubber. It is common knowledge now that the_______(64) to make rubber hard and strong is by heating it with sulfur. It took Goodyear four more years to find this method. When at last he did it, he had_______(65) at all. Everythin
