from the dishes and pots. When grease is hot it is liquid, you know, but when it gets into the cold pipe it cools into a solid cake. Often when the pipe is stopped the plumber will take a whole handful of grease out of the trap.

"Is that why you told me not to pour the grease from the frying-pan into the sink?" asked Paul.

"Partly because of that and partly because we never waste any grease, but use it again or make soap of it," said Mother. "You see, being thrifty really helps in being clean and being healthy, for wastefulness is likely to mean a houseful of unused things that collect dirt, a garbage pail full of decaying food and pipes full of valuable grease.

"Suppose there isn't any plumber and you can't get the pipe open," said Ruth.

"I pour a lot of very hot water with washing soda in it down the pipe. The soda turns the grease into a sort of soap and the hot water washes it away, down the pipe. By the way, if you ever unscrew a trap, be sure to have a pan underneath, or you will have a flood of water on the floor."

"Dear me," exclaimed Paul. "Seems to me plumbing is lots of bother. I think I'd rather be an Indian and just wash in a brook and not bother with any old pipes."

"All right," said Ruth, promptly, "you can go and live like an Indian with Jim Nixon, and I'll keep house here. I just love the play-house-pipes and all."

THINGS TO DO

Try Mrs. Weston's experiment. Have you ever seen liquids run up through tiny pores in paper or cloth? Anywhere else? Scientific people call this capillarity. It helps us blot our letters, burn oil through lamp wicks, helps plants get water from soil.

Try these experiments also. They will help to understand this chapter. Collect two tumblers and a piece of clean rubber piping. Fill one tumbler with water. Place this tumbler on a pile of books and stand the empty tumbler below it. Then put the rubber tube in the glass of water and suck on it till the tube is full of water. Keep one end under water in the first glass. Hold the other end shut and lower this end into the empty tumbler. What happens? You have made a siphon. Have you ever seen one used? For what? Do you notice that by it you can make water run "up hill" over the bend in the tube? Find a siphon in the kitchen or bathroom plumbing. Experiment with your siphon to find out what will prevent it from working well.

If your teacher can get you a "thistle" tube and can put two bends in it like a letter N you can then see how a water-trap works. Pour some colored water quickly into the thistle end of the tube. How does the water act? Have you a siphon? Find the "trap" that catches the water. Do you see that it would act like a stopper to keep back the smells?

THINGS TO REMEMBER

Sewage and all waste water must be removed from our homes. In the city the sewage from the house is gathered into a drain pipe. This drain pipe runs underground to the street sewer. This sewer joins the great main sewers which carry off the waste material.

In the country it is wise to have drain pipes also. These drain pipes should carry the sewage into a cesspool.

The cesspool is a tank underground with brick and cemented walls that must not permit any sewage to escape into the soil. Sewage may contain typhoid or other disease germs. We know that these may make water supplies dangerous if they get into the ground and water. If sewage is kept in a tight cesspool the sewage decays and is changed into gas and water. The disease germs will die in time with all their food gone. The gas and water can then safely be carried off underground by a second pipe.

In our houses we prevent unpleasant sewage smells from coming into our rooms by water traps in the waste pipes. These traps are little siphons such as you made in your experiments. These traps can be opened, in case they should become stopped up through carelessness. To keep a trap working, remember:

1. Never to throw rags or strings into basin, tub or toilet.

2. Never to throw grease into a basin-it is wasteful as well as careless.

3. Run washing soda and hot water through the trap once in a while to cleanse it.

4. Always run clean water through the pipes after using a basin, etc.

TO THINK ABOUT

How is the waste from your house removed? What does your city do with its sewage?

What happens to sewage in a cesspool? Why must people be very careful to have cesspools and drains very carefully and tightly built to prevent leaking?

Find the "traps" in your plumbing at home. How do they work? Did the experiment made explain this to you?

Why do houses that haven't been occupied a long time sometimes have a smell of "sewer gas" in them. What happened to the traps?

What can you do to keep your traps at home working?

CHAPTER VII

HOW THE HOUSE WAS LIGHTED

"WHAT did people do before electric lights were invented?" asked Paul. Having spent the afternoon helping Uncle George to put in the wires for the electric lights in the play-house, he felt that he had earned an extra slice of cake for supper.

Mother passed him the cake-plate as she answered, "I suppose the very earliest men of all, who lived in caves and tree-tops, just picked a piece of burning wood out of their fire and carried it for a torch."

"But that wouldn't be much good if you wanted to read or sew," said Ruth.

"No, but cave and tree-top people have no books and very little clothing, and go to bed with the birds, so they have hardly any need of light in their houses,' replied Father.

"Why did you put electric lights into the playhouse, when we have to have gas anyhow to cook with in the kitchen?" asked Ruth.

"Because," said Father, "gas uses up the air— a gas jet may use up as much air as two people. Then, too, it makes the room hot, and besides the gas jet may possibly leak and gas is very poisonous. We have to use it in the kitchen to cook with, but you children will have to be very careful."

"I read about a man who had never seen gas,

said Paul, "and when he went to bed he blew it out and it killed him."

"There are not many people nowadays who would do that," remarked Mother, "but many people are very careless about turning the gas entirely off. Always turn the gas-key just as far as it will go and when you light the gas, strike your match

first. Don't turn the gas on and then go hunting for a match, as I've seen some people do."

"But, Mother, what did they do before someone invented gas?" persisted Ruth.

"The first lights were lamps," said Mother. "Don't you remember that lovely old Roman lamp that Professor Fielding showed us? Almost as soon as people began to build real houses they needed lights, for the early houses had very few windows and very tiny ones. The first lamps were made of pottery or bronze and filled with olive oil or some sort of vegetable oil or animal fat, for kerosene was unknown in those days. The wick floated in the oil and made a feeble light."

"Oh, yes," cried Paul. "Our teacher told us a