"Well, I had no idea that it would take us a whole day to get enough
dirt for an analysis," remarked Mr. Thornton, as they were
collecting the samples late in the afternoon. "Five minutes would
have been plenty of time for me, before I saw the holes you've bored
to-day."

"The fact is," replied Percy, "that the most difficult work of the
soil investigator is to collect the samples. Of course any one could
fill these little bags with soil in five minutes, but the question
is, what would the soil represent? It may represent little more than
the hole it came out of, as would be the case where the soil had
been disturbed by burrowing animals, or modified by surface
accumulations, as where a stack may sometime have been burned. In
the one case the subsoil may have been brought up and mixed with the
surface, and in the other the mineral constituents taken from forty
acres in a crop of clover may have been returned to one-tenth of an
acre."

"Certainly such things have occurred on many farms," agreed Mr.
Thornton, "and they may have occurred on this farm for all any one
knows."

"Fifty tons of clover hay," continued Percy, after making a few
computations, "would contain 400 pounds of phosphorus, 2400 pounds
of potassium, 620 pounds of magnesium, and 2340 pounds of calcium."

"I don't see how you keep all those figures in your head," said Mr.
Johnston.

"How many pounds are there in a ton of hay?" asked Percy.