“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.