推荐回答(2个)
叶脉标本的制作
叶脉标本可用做教具,由于标本美观,也常做书签使用,所以叶脉标本又称做叶脉书签。具体制作方法如下:
(1)煮制法
选择叶脉粗壮、细密、叶肉较厚的叶片备用。用一只烧杯盛清水200mL,水中放人碳酸钠5g、氢氧化钠7g,在火上加热。煮沸后把叶片投入杯中,大约煮沸10min。在此过程中,要用镊子轻轻摆动叶片,使叶片均匀地受到腐蚀。煮好后将叶片夹出,放人盛有清水的玻璃缸中,用软毛牙刷(最好是鬃牙刷)刷去叶片中叶脉以外的部分,露出叶脉,然后放人漂白液内漂自(即将8g漂白粉溶在40mL水里,再将6g碳酸钾溶在30mL沸水里,然后将两液混合、摇匀,冷却后加入100mL水,过滤后则成为漂白液)。漂白后,可根据需要将叶脉标本染成各种颜色。
(2)腐烂法
将上述适于制作叶脉标本的叶片放人水中浸泡,注意要将浸泡装置放在温暖处,以便利用细菌使叶片中叶脉以外的部分腐烂。以后的步骤同煮制法。水腐时应注意浸液发臭时要换水。此法制作时间长,但简便易行。
附录:
叶脉书签制作方案
制作原理:叶片的叶肉部分容易腐烂降解,而叶脉非常坚韧,能构成各种形状比如网状、扇形、弧形等结构,以支持叶片。选取具网状脉的植物叶片,用氢氧化钠等碱溶液加热煮沸,可以水解掉叶肉等部分,仅剩下网状脉,再利用过氧化氢的强氧化性将叶脉漂白,一件精美的叶脉书签便制作成功了。
工具材料:(1)5-10%的氢氧化钠溶液,5%的过氧化氢溶液;
(2)电热套、烧杯(多个)、瓷盘、旧牙刷、镊子、水彩色;
(3) 采摘新鲜的具网状脉的植物叶子,如白玉兰、杨树、白蜡等。
制作步骤:(1) 实验前采摘新鲜的树叶(以白玉兰叶为佳),落叶也可择优选用,应注意采摘树叶时要爱护植物;
(2) 用电热套加热氢氧化钠溶液,直至沸腾;
(3) 选5—10片大小适合的树叶放进煮沸的碱液中,要不停地将叶子摁到水下,直至沸腾,保持沸腾10分钟;
(4) 不时地用镊子拿出叶子,用手感觉叶肉是否煮烂;
(5) 在瓷盘里加适量水,将已煮烂的叶片放到其中,用旧牙刷刷叶肉,刷时先刷正面,按从左向右,从叶柄向叶尖,从主脉向侧脉有序地刷,直至刷掉叶肉;再将叶片翻转,用同样的方法刷,直至只剩下网状脉;
(6) 将叶脉放到盛清水的烧杯中,洗去残渍;
(7) 将洗尽的叶脉放到盛有5%的过氧化氢溶液中,放置24小时;
(8) 24小时后,叶脉便被漂白,从过氧化氢溶液中取出叶脉,放到标本纸中压干、压展;
(9) 将红水彩放到培养皿中,用水稀释3倍,并用毛笔刷到叶脉上,然后晾干;
(10) 将已涂色的叶脉标本进行压膜,各人还可根据自己的爱好进行艺术处理,这样一个精美的叶脉书签就制作成功了。
注意事项:(1)由于过氧化氢具有强氧化性,进行制作时应注意安全,最好戴橡胶手套进行;
(2)刷叶脉时应掌握力度,以免刷破;
(3)经过制作经验,白玉兰叶最适宜于制作叶脉标本,杨树叶与白蜡叶也可以做,只是效果差一些;
(4)用落叶制作时,氢氧化钠浓度应较高,而用新叶时可以浓度低点;
(5)由于氢氧化钠价格较贵,可以考虑用石灰水或碱面代替。
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