“I use this acid to test the soil for the presence or absence of limestone.  Ordinary limestone consists of calcium carbonate.  Here, again the chemical name alone is sufficient to indicate the elements that compose this compound.  It is only necessary to keep in mind the fact that the ending _-ate_ on the common chemical names signifies the presence of oxygen Thus calcium carbon_ate_ is composed of the three primary elements, calcium, carbon and oxygen.

“Of course the chemical element is the simplest form of matter.  An element is a primary substance which cannot be divided into two or more substances All known matter consists of about eighty of these primary elements; and, as a matter of fact, most of these are of rare occurence—­many of them much more rare than the element gold.

“About ninety-eight per cent. of the soil consists of eight elements united in various compounds or combinations; and only ten elements are essential for the growth and full development of corn or other plants.  If any one of these ten elements is lacking, it is impossible to produce a kernel of corn, a grain of wheat, or a leaf of clover; and in the main the supply is under the farmer’s own control.  But we can discuss this matter more fully later.  Let us see what we have here.”

Percy poured a few drops of the hydrochloric acid into the hollow of the cake of soil.

“What should it do?” asked Mr. West.

“If the soil contains any limestone, the acid should produce foaming, or effervescence,” replied Percy; “but it is very evident that this soil contains no limestone.  You see the hydrochloric acid has power to decompose calcium carbonate with the formation of carbonic acid and calcium chlorid, a kind of salt that is used to make a brine that won’t freeze in the artificial ice plants.  The carbonic acid, if produced at once decomposes into water and carbon dioxid.  Now, the liberated carbon dioxid is a gas and the rapid generation or evolution of this gas constitutes the bubbling or foaming we are looking for; but since there is no appearance of foaming we know that this soil contains no limestone.”

“Then you have already found that those three elements,—­calcium, carbon, and oxygen, you called them, I think—­you find that those elements are all lacking in this soil.”

“No, this test does not prove that,” said Percy.  “It only proves that they are not present as limestone.  Calcium may be present in other compounds, especially in silicates, which are the most abundant compounds in the soil and in the earth’s crust; and, as indicated by the ending _-ate, oxygen is contained in calcium silicate as well as in calcium carbonate.”

“I see; the subject is much more complicated than I thought.”

“Somewhat, perhaps,” Percy replied; “but yet it is quite simple and very easily understood, if we only keep in mind a few well established facts.  Certainly the essential science of soil fertility is much less complicated than many of the political questions of the day, such as the gold standard or free-silver basis, the tariff issues, and reciprocity advantages, regarding which most farmers are fairly well informed,—­at least to such an extent that they can argue these questions for hours.”