"I have a tumbler here, filled with water to the brim. I want you to stir it gently, while I put some salt into it-a spoonful at a time. Are you ready? One, two, three, four, five, six. Now we must be careful-seven. I have put seven spoonfuls of salt into the tumbler of water. But if you look you will see some of the salt is now settling at the bottom.""I suppose," said Norah, "the salt that sinks to the bottom is not dissolved.""That"s right," said Fred. "The rest of the salt is all dissolved; we cannot see it.""But, Fred," said his sister, "the tumbler was full to the brim at first. If you had put seven spoonfuls of water in, it would have run over the top. How have you been able to put seven spoonfuls of salt in?""Ah," said Willie, "that"s the funny part of it.
"The water is porous. As the salt dissolves it breaks up into such tiny morsels, that they can find their way into the pores of the water. When these pores are all filled, the water can dissolve no more salt. The rest sinks to the bottom in a heap.""Now we"ll empty this away, and do the same with some lime." said Fred.
