l6 THE FAIRY-LAND OF SCIENCE. 
as it can find wherever it can penetrate. Such simple 
things as these you must learn from books and by 
experiment. 
Then you must understand what is meant by 
chemical attraction; and though I can explain this 
roughly here, you will have to make many interesting 
experiments before you will really learn to know this 
wonderful fairy power. If I dissolve sugar in water, 
though it disappears it still remains sugar, and does 
not join itself to the water. I have only to let the 
cup stand till the water dries, and the sugar will 
remain at the bottom. There has been no chemical 
attraction here. 
But now I will put something else in water which 
will call up the fairy power. Here is a little piece of 
the metal potassium, one 
of the simple substances 
of the earth ; that is to 
say, we cannot split it 
up into other substances, 
wherever we find it, it is 
always the same. Now if 
Piece of potassium in a basin of I put this piece of potas- 
sium on the water it does 
not disappear quietly like the sugar. See how it rolls 
round and round, fizzing violently, with a blue flame 
burning round it, and at last goes off with a pop. 
What has been happening here ? 
You must first know that water is made of two 
substances, hydrogen and oxygen, and these are not 
merely held together, but are joined so completely 
that they have lost themselves and have become 
