"As you know this, I don"t think it will surprise you to hear what I am now going to tell you. If tar isheated in a closed retort, some of it rises and passes away in the form of vapor.
"The vapor is carried along pipes into a cool chamber called a condenser. As it condenses it forms a new liquid, which is very highly inflammable, and is used for lighting purposes. It is called coal- naphtha.
"That which is left behind in the retort is the solid substance which we call pitch.""What a wonderful substance coal is after all," said Norah.
SUMMARY
Smoke, as well as gas, is given off from the burning coal at the gas-works. It is all made to pass through water. The gas is very light, and rises to the surface to be carried away in pipes. The smoke is heavy, and sinks to the bottom as tar. Tar is a thick, black, heavy liquid, something like molasses. It has a powerful smell and a bitter taste. It is insoluble in water. It is very in?ammable. Coal-naphtha and pitch are got from tar.
Lesson 39
The Fish and its Food
"Isn"t there something else you would like tolearn about the fishes, Norah?" asked Fred.