"No, it costs much less to grind it than to burn it," Percy replied. "Mills are used for grinding rock in cement manufacture, and the rock phosphate and bone meal must all be ground before using them either for direct application or for the manufacture of acidulated fertilizers; and limestone is not so hard to grind as some other rocks. Furthermore it does not need to be so very finely ground. If fine enough so that it will pass through a sieve with ten meshes to the inch it does very well. That you see would be a hundred meshes to the square inch; and, of course, a great deal of it will be much finer than that. In fact the ground limestone used in the Pennsylvania experiments was only fine enough so that about ninety per cent. of it would pass a sieve with ten meshes to the inch, and yet the limestone gave decidedly better results than the burned lime, and it is not nearly so disagreeable to handle. Besides this, the ground limestone is much less expensive. It can be obtained at most points in Illinois for about a dollar and fifty cents a ton." "A dollar and fifty cents a ton!" exclaimed Mr. Thornton. "Well, that is cheap, but how about the freight and the barrels and bags? Freight is a big item with us." "The dollar and fifty cents includes the freight," was the reply. "Includes the cost and the freight both?" "Yes, and the Illinois farmers have it shipped in bulk, so there is no expense for barrels or bags. Of course the supplies of both coal and limestone are very abundant, and with a well-equipped plant the actual cost of grinding does not exceed twenty-five cents a ton. The original cost of the material ground and on board cars at the works varies from about sixty cents to one dollar a ton, and this leaves a very fair margin of profit. "The men who furnish the ground limestone realize that very large quantities of it are needed if the soils of Illinois are to be kept fertile, and they also realize that the ultimate prosperity of the country depends upon agricultural prosperity. Their far-sightedness and patriotism combine to lead them to try to sell carloads of limestone instead of tons of burned lime. As a matter of fact five or ten dollars profit on a car of limestone, the use of which in large quantities is thus made possible in systems of positive soil improvement, is very much better for all concerned than a profit of half that much on a single ton of burned lime which is used as a soil stimulant in systems of soil exhaustion." "It is certainly true," said Mr. Thornton, "that all other great industries depend upon agriculture, directly or indirectly. I have thought of it many times. It seems to me that fishing is about the only exception of importance." Mr. Thornton requested that Percy remain for lunch in order that they might return to the field to let him see the soil acidity tests made. CHAPTER XIII WHY PERCY WENT TO COLLEGE