title="8"/> happen. Soon a cloud was seen over the dish, and by and by all the water had gone.

“But what is that at the bottom of the dish?” asked Uncle George.

“It looks like powder,” said Frank.

“And it must have been in the water all the time,” added Tom.

Evaporating Salt Water.

“And yet the water was clear,” said Uncle George. “Look once more.”

As he spoke, Uncle George took a glass of clean water from the tap. He put two large spoonfuls of salt in, and stirred it up.

“You see,” he said, “the salt has gone from sight. Still the water is clear. Where has it gone?”

“Into the water,” said Tom.

Uncle George put more salt in the water, and stirred it up. He kept on doing this until the water would take up no more salt, no matter how much it was stirred. This he called brine.

“Now, Frank, please go and ask mother for a fresh egg,” he said, “and you, Tom, please bring me some fresh water in another glass.”

Egg floating in Salt Water.

Uncle George placed the egg in the glass in which the salt had been put, and it floated in it. He then placed the egg in the glass of fresh water, and it at once sank to the bottom.

“Can you explain this!” he said.

“The salt water is heavier and thicker than the fresh water. That is why it bears up the egg,” said Frank.

“That is very good indeed, Frank. That is just the reason. The salt water or brine is denser, or heavier, than the other.”

Uncle George next took a glass tube with a thistle-shaped bulb at the end of it. Frank kept his finger on the small end, while his uncle poured some of the brine into the bulb. He next tied a piece of bladder skin over the bulb, and placed it in a glass of fresh water, so that the salt water in the tube was at the same level as the fresh water in the glass.

Then he took two small glass bottles. He filled one with fresh water and the other with brine, and tied a piece of bladder skin over the mouth of each. The one which was filled with brine he placed in a larger dish of fresh water. The other, that is the one filled with fresh water, he placed in a dish of brine.

“Now, children, we will go and have tea,” he said, “and when we come back we will see if any change has taken place.”

About an hour later Uncle George, Dolly, and the boys came back.

“Oh,” said Frank, “look, Uncle George! The water has risen up in the thistle tube.”

“Yes, how do you account for that, Frank?”

“Some of the fresh water has passed through the skin,” Frank answered.

“Now taste the water in the glass outside the skin,” said Uncle George. “It was fresh water when we put it in, wasn’t it?”

Frank did so. Tom tasted it too. Both boys declared that it was now salt.

“Where did the salt taste come from?” their uncle asked.

“It must have come through the skin,” said Tom.

“Then some of the salt water in the thistle tube has passed through the skin into the glass; and some of the fresh water in the glass has passed through the skin into the thistle tube. Can you tell me any more?”

Frank thought for a little while and then said, “Oh yes, more fresh water than salt water has passed through the skin, because the salt water is now far up the tube.”

“Quite right, my boy. Now let us look at the small bottles. The skin on the one filled with brine is swollen out like a ball, while the water in the dish tastes salt. The skin of the other is drawn far in, showing us that much of the fresh water which it contained has passed out. If you taste the water in this bottle, you will find that a very little of the brine in the dish has passed into it through the skin.

“Now what we learn from these things is really this—that when two liquids, a heavy and a light one, are separated by a thin skin, they both pass through the skin. The heavy liquid passes through slowly, and the light liquid passes through quickly.”

Uncle George then placed some small seeds on a piece of wet blotting-paper. He turned a glass tumbler upside down, and placed it over them.

“We will leave these for a few days,” he said.

Questions and Exercises.

1. Boil some river-water in a flat dish until all the water is gone. Do the same with some sea-water, or, if this is not at hand, make some brine. Examine the two dishes, and tell what you see.

2. Take a glass gas chimney, and tie a piece of bladder, or parchment, over one end of it. Half fill it with sugar and water. Now place it with its tied-up end bottommost in a tumbler of clear cold water. After an hour or so taste the water in the tumbler. What have you to say about it?

3. What takes place when brine and clear water are separated from one another by a piece of skin (parchment)?

A Box of Mustard Seeds.

II.—HOW PLANTS TAKE FOOD FROM THE SOIL (2).

A whole week went by before Uncle George was ready for the next lesson.

At last he called the children and said to them—“Tom, will you please fetch me the seeds which we put on the wet blotting-paper under the tumbler? Frank, bring me two leafy branches from a rose-bush in the garden; and, Dolly, please fetch two glasses from the kitchen.”

Now there was nothing the children liked better than to help their Uncle George, and all three rushed off at once to do his bidding.

While they were away Uncle George himself went into the garden, dug up two young plants, and brought them to the children in the study.

Sun-flower Plant in Water.

“Now, children,” said Uncle George, “we are ready to begin our lesson. Fill one of the glasses with water, Frank, and put one of your leafy rose branches in each glass—one branch in water and the other in a dry glass. Can you tell me what will happen to the branches?”

The children had many times seen what had happened to flowers when the maid had forgotten to put water in the vases, so that Tom readily said, “Yes, the one in the dry glass will wither, while the one in the water will keep fresh for some time.”

“How do you know that?”

“Because it always happens, Uncle,” said Frank. “Why, sometimes the flowers we gather in the wood are faded before we get home. They often come back to life when put in water.”

“You are quite right, Frank,” Uncle George replied. “See, here are two young sun-flower plants, which I brought in from the garden. I placed one in water. The other I left lying on the table. The one on the table is dead. What does this show us?”

The Sun-flower, faded.

“That plants