英文科學讀本 第三冊·Lesson 34 More about Coal-Gas

Lesson 34 More about Coal-Gas

Teacher made some coal-gas for us at school today, Norah, said Willie, "and it brought to my mind one of our very early lessons. Do you remember that we once made some gas in one of father's long clay pipes?"

Yes, of course I do, said Norah, "and when you put a match to the stem of the pipe the gas burned there as it came out."

Teacher made some gas in this way, only ever so much better than we could do it. Suppose we tell you all about it, said Will.

Well, said Fred, "teacher had a long clay pipe filled with coal broken very fine, and closed up with clay just as we had. He fixed the bowl of the pipe over the flame of a gas-burner standing on the table. He turned the stem of the pipe so as to make the end of it dip into a bowl of water."

He then filled a glass tube with water, and turned it upside down in the basin, taking care to keep the mouth of the tube below the surface of the water, and just over the end of the pipe stem. The water did not run out of the tube, but remained in it, while he held it there.

Presently, as the bowl of the pipe got red-hot, the gas began to come out of the stem, and you should have seen what took place then. The gas rose through the water in little bubbles, and the bubbles ran up the tube one after another. As they ran up, the water began to flow out of the tube into the basin. In a little while it was all gone, and the tube was full of gas instead.

Yes, and we knew it was really the coal-gas, said Will, "because when teacher took the tube out of the water and put a light to the mouth of it, it took fire and burned."

Teacher says this is just the way the gas is made at the great gas-works.

Instead of the bowl of the pipe with its pinch of coal-dust, they have large, strongly-built, closed chambers called retorts, made of firebrick and iron, each one holding nearly a quarter of a ton of coal.

Instead of the stem, they have long iron pipes, and instead of the little glass tube, they have enormous iron gas-holders, many times bigger than our school.

SUMMARY

To make coal-gas, the coal is heated in closed retorts, and the gas and smoke are allowed to pass away by long pipes, into great receivers, to be purified. The cinders left from the burning are coke.