[题目]在一只试管里放置一定量的草酸铁后,在小火上加热,草酸铁便放出CO_2和H_2O,试管里残留下微细的铁粉。将这些铁粉倒入空气中时,铁粉会成为着火的粉末落下。这就是说,这样制得的铁粉能自动着火,而平时我们即使用火来点燃一块铁,铁也不会着火,试 [Subject] After placing a certain amount of iron oxalate in a test tube and heating it over a small fire, iron oxalate releases CO 2 and H 2 O, and fine iron powder remains in the test tube. When the iron powder is poured into the air, the iron powder will fall as a powder of fire. This means that the iron powder thus produced will automatically catch fire, and at ordinary times we will use fire to light a piece of iron, and iron will not catch fire.