M:Before we begin the tour of the factory,do you have any more questions?
W:Yes,I have one.I would like to know the exect difference between crystal and glass.
M:Well,real crystal is generally a hard substance in which the atoms are arranged in a highly ordered structure much like the frame work of a shyscraper.
W:Is that mean that in ordinary glass the molecules are not ordered?
M:That's right.But most of the glassware made here is actually lead crystal or glass with a high lead content.
W:Lead! Isn't lead poisonous?
M:Not when it's mixed with glass.What it does is to make a very good quality glass. I'll be showing you samples of several kinds of glass on our tour. If everyone is ready,we'll begin now,please follow me.