How can they turn nitrogen into a liquid?
Boiling water, changing into steamy gas, is a whole lot hotter than frozen ice. But the ice is almost twice this much hotter than liquid nitrogen. While water is boiling and freezing, free nitrogen remains an airy gas. It must be chilled and then chilled a lot more before it changes into a watery liquid. The ingredients for creating liquid nitrogen are as plentiful as the air itself. In fact the best ingredient for the job is ordinary air, cleaned and free of most of its impurities. It is, of course, a mixture of gases and about four fifths of it is gaseous nitrogen. Almost all the rest of it is gaseous oxygen. The ingredients are cheap and plentiful but the operation of changing these gases into liquid air is very costly. They are chilled together below their boiling points and then separated as the liquid nitrogen evaporates back to its gaseous form. The gaseous, liquid and solid states of mater are related to changes in temperature. This is because they are made of molecules and the
