"The gas is lighter than the water, and it bubblesup to the surface and is carried off, to be collected into the great gasometers. The water condenses the smoke, and it falls to the bottom of the tank as a thick black liquid.
"What do you think this is, Norah? It is tar. I had no idea what tar was till today. I am glad I know.
"Father has given me some tar in this old cup. Let us look at it. It is a thick, black, shiny, sticky liquid, something like molasses to look at. It has a powerful smell and a bitter taste.
"Look what happens if I put a drop of it on my hand. I cannot rub it off. I cannot wash it off. Some grease or turpentine will remove it, because tar is soluble in fat and turpentine, but it is insoluble in water.
"If I drop a little in this glass of water you will see that it sinks to the bottom. It will not mix with the water. It is heavier than the water. You know I told you that the people at the gas-works always find the tar at the bottom of the tank.
"Now watch while I dip this piece of stick in the tar and set light to it. It sends off dense clouds of smoke and blazes up in an instant. It is very inflammable.
