Uncle George had taught his little friends many things from what he
called the Book of Nature, and what they had learnt made them eager to
know more.
One day as Dolly, the boys, and Uncle George were in the garden they saw
that a tulip, which the day before was in full bloom and strong, was now
lying dead on the ground.
“Poor little tulip!” said Dolly. Both the boys were sorry too. They had
watched it come through the ground like a blade of grass, open out its
bud, and expand its bloom. Now all was over. The little flower would no
longer enjoy the bright sunshine or the rain. It would no longer send
forth its rootlets in search of the food it so much liked.
“Have you ever thought, Dolly, how the tulip, and indeed all plants,
take their food from the soil?” asked Uncle George.
“I know they _must_ feed in some way,” said Dolly, “or they would not
grow. But I do not know how they do it.”
“Should you like to know, Dolly?” asked Uncle George.
“Indeed I should,” said the little girl.
The boys were just as eager as Dolly to know about this, so Uncle George
and the children went indoors for a lesson.
“I cannot tell you how plants take their food from the soil without
first of all showing you what happens when water and soil are mixed
together in a tumbler,” said Uncle George. “Tom will fetch me a tumbler,
and you, Frank, bring me a little water.”
When these were brought, Uncle George put a spoonful of soil into the
tumbler, and then poured some water on it.
“Stir it up, please, Dolly,” said Uncle George, “and you may pretend you
are going to make a pudding.”
Dolly did so.
“Now let us put it aside for a few minutes, while we place the flowers
we have gathered into the vases,” said Uncle George. “Then we will look
at our tumbler of muddy water.”
How pretty the flowers were made to look! How fresh they were! and how
pleasant was their scent! The children hardly thought of the tumbler,
but Uncle George was ready now for the lesson.
[Illustration: Glass of Mud and Water.]
“Look! look, at the tumbler,” said he. “Do you see a change?”
“Indeed we do,” said all the children in one voice.
“The mud has sunk to the bottom of the glass,” added Tom, “and the water
on the top is clear.”
Uncle George poured some of the clear water into a clean flat dish. Then
he took a spirit-lamp from a little cabinet, and heated the water in the
dish with it.
The children watched to see what would 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.
[Illustration: 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.”
[Illustration: 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)?
[Illustration: A Box of Mustard Seeds.]