人教版小学三年级上学期第四单元习作范文写一篇观察日记300字左右

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坐坐坐，制作组

游客 111.73.148.x 发表于 2014-11-10 20:31
坐坐坐，制作组

爱迪生和他的助手们，用白金试了好几次，可这种熔点较高的白金，虽然使电灯发光时间延长了好多，但不时要自动熄掉再自动发光，仍然很不理想。　　爱迪生并不气馁，继续着自己的试验工作。他先后试用了钡、钛、锢等稀有金属，效果都不很理想。　　接下来，他与助手们将这1600种耐热材料分门别类地开始试验，还是采用白金最为合适。由于改进了抽气方法，使玻璃泡内真空。灯的寿命已延长到2个小时。但这种由白金为材料做成的灯，价格太昂贵了，谁愿意化这么多钱去买只能用2个小时的电灯呢？　　爱迪生看到这用棉纱织成的围脖，爱迪生脑海突然萌发了一个念头：　　对！棉纱的纤维比木材的好，能不能用这种材料？　　他急忙从围巾上扯下一根棉纱，小心地把这根炭丝装进玻璃泡里，效果果然很好。　　爱迪生非常高兴，制造了很多棉纱做成的炭丝，进行多次试验。灯炮的寿命延长13个小时，后来又达到45小时。　　“我希望它能亮1000个小时，最好是16000个小时！”爱迪生说道。　　最后，爱迪生终于选择了竹子。他先取出一片竹子，装进玻璃泡，通上电后，这种竹丝灯泡竟连续不断地亮了1200个小时！　　他终于做出了自己满意的电灯。