Here he took out a spoonful of the whiting, and put it into a little saucer, and poured some water upon it, and stirred it.
"There you have a mixture similar to sugar and water, or salt and water; the ingredients are very closely mixed, but they are not united to form any different substance; if it should stand a while, the water would evaporate, and leave the same amount of real whiting.—But now I will pour some vinegar on the whiting in the cup, and you will see a difference."
Johnny poured some vinegar from the vial into the cup, and stirred the mixture with the spoon.
"You see all those bubbles? Those are bubbles of a kind of gas; as fast as they break, the gas that has been formed by the chemical union of the vinegar and whiting will pass into the air, and what is left in the cup will not be vinegar and whiting; there will be no real vinegar and no real whiting left; parts of each have united to make the gas; so each has lost something peculiar to itself, and cannot be the very same article that it was before."
"Some of the bubbles are real big, and you can't break them easily with the spoon," said Sue, who was stirring the mixture curiously. "I wish my soap-bubbles would be as tough."
"Now," continued Johnny, "mixing the whiting and the vinegar caused a real chemical union: two substances united to make a third substance entirely different from the two original ingredients."
"I think I understand what a chemical union is now," said Alec.
"And so do I," said Belle.
"This would be a beautiful experiment to illustrate a chemical union, if it were not so very common," continued Johnny.
As he spoke, he took a match from a match-safe he had placed on the table, struck it against the edge of the table, and held it out, smiling playfully.