loam, or sandy loam. Pure sand soil weighs about one-fourth more,
while pure peat soil weighs only half as much as normal soil."

"I wish you would tell me," said Mr. Thornton, "what the fertilizers
cost that have been used on that Rothamsted wheat field."

"The annual application of nitrogen has been one hundred twenty-nine
pounds per acre," said Percy. "What will it cost?"

"Well, at twenty cents a pound, it would cost $25.80," was Mr.
Thornton's reply after he had figured a moment. "But why didn't they
grow clover and get the nitrogen from the air?"

"For two reasons," replied Percy. "First, when those classic
experiments were begun by Sir John Lawes and Sir Henry Gilbert in
1844, it was not known that clover could secure the free nitrogen
from the air; and, second, the experiment was designed to discover
for certain whether wheat must be supplied with combined nitrogen,
by ascertaining the actual effect upon the yield of wheat of the
nitrogen applied."

"And what was the actual effect of the nitrogen?" questioned Mr.
Thornton. "How much did the wheat yield when they left out the
nitrogen and applied all the other elements?"

"Only fifteen bushels," was the reply.

"Only fifteen bushels! Only two bushels increase for all the other
elements, phosphorus, potassium, magnesium, and calcium,--and I
remember you said that sulfur also was applied. Why didn't they