"Any other farmer can make these tests as well as I can," said Percy. "This bottle of acid cost me fifteen cents and it can be duplicated for the same price at almost any drug store. The acid is very concentrated, in fact about as strong as can easily be produced, but it need not be especially pure. Some care should be taken not to get it on the clothing or on the fingers, although it is not at all dangerous to handle, but it tends to burn the fingers unless soon removed, either by washing with water or by rubbing it off with the moist soil." "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."