"Well, most people around here who use fertilizer buy what the agent
calls two-eight-two, and its costs about one dollar and fifty cents
a hundred pounds; but it can be bought by the ton for about
twenty-five dollars."

"'Two-eight-two' means that the fertilizer is guaranteed to contain
two per cent. of ammonia, eight per cent. of available 'phosphoric
acid,' and two per cent. of potash."

"Ammonia is the same as nitrogen, is it not?"

"No, it is not the same," replied Percy. "Ammonia is a compound of
nitrogen and hydrogen. In order to have a clear understanding of the
relation between ammonia and nitrogen we only need to know the
combining weights of the elements. The smallest particle of an
element is called an atom. Hydrogen is the lightest of all the
elements and the weight of the hydrogen atom is used as the standard
or unit for the measure of all other atomic weights; thus the atom
of hydrogen weighs one."

"One what?" interrupted Mr. Thornton.

"No one knows," replied Percy. "The atom is extremely small, much
too small to be seen with the most powerful microscope; but you know
all things are relative and we always measure one thing in terms of
another. We say a foot is twelve inches and an inch is one-twelfth
of a foot, and there we stop with a definition of each expressed in
terms of the other, and both depending upon an arbitrary standard
that somebody once adopted; and yet, while the foot is known in most
countries, it is rare that two countries have exactly the same