A、Lots of gas in a very short period. B、Great lifting charges of fireworks. C、A fountain of sparks,gas and smoke. D、Flames burni

M: Fireworks,dazzling displays,I wonder how they work?
W: It actually depends on a rather simple technology: an explosive mixture known as gunpowder. It shoots fireworks into the air and propels bullets from guns.
M: It was the Chinese that first discovered gunpowder, right?
W: Quite so,over 1,000 years ago. (22) The Chinese used it to make firecrackers. Marco Polo said they believed the noise had the power to scare away evil spirits.
M: Indeed,it’s such a dreadful noise,but how exactly does the black powder,gunpowder,make all those shapes and colors?
W: Aha,(23) the shapes and colors are sparks and gas and smoke produced in the process of burning,and a relatively slow one, so you can see it in the air. If it burnt too quickly it would all be over and it would be a pointless firework.
M: OK,I see.
W: The gunpowder is a mixture of three components. If you mix them together you end up with a powder in which you can still see the same particles.
M: (24) So, change the combination, and we get a different firework composition, and so on.
W: You got it fast. Now we press the powder into a cake and burn it,the fire can travel all directions and the whole reaction is very quick. This sort of thing is used for making the lifting charges of fireworks, where you want lots of gas in a short space of time.
M: (25) And if we take the powder but compress it into some other shape,say a tube,what will we get?
W: (25) Then we’ll get a little fountain. It only burns on the top surface.
22. What did the Chinese first use firecrackers for?
23. What are the colors and shapes of fireworks?
24. How do we make different colors of fireworks?
25. What will we get if we press the gunpowder into tubes?