“The limestone must be quarried whether used for grinding or for burning, and the grinding can be done for twenty-five cents a ton where a large equipment with powerful machinery is used and where cheap fuel is provided, as near the coal mining districts.  It need not be very finely ground.  If ground to pass a sieve with twelve meshes to the linear inch, it is very satisfactory, provided that all of the fine dust produced in the grinding is included in the product.  You see the soil acids are slightly soluble and they attack the limestone particles and are thus themselves destroyed or neutralized.  If, however, you ever wish to use raw rock phosphate, insist upon its being sufficiently fine-ground that at least ninety per cent. of it will pass through a sieve with ten thousand meshes to the square inch, this being no finer than is required for the basic slag phosphate, of which several million tons are now being used each year in the European countries.  Like the raw rock phosphate, the slag gives the best results only when used in connection with plenty of decaying organic matter.”

“That reminds me,” said Mr. West, “of what one of the fertilizer agents said about raw phosphate.  He said the use of raw phosphate with farm manure reminded him of ‘stone soup,’ which was made by putting a clean round stone in the kettle with some water.  Pepper and salt were added, then some potatoes and other vegetables, a piece of butter and a few scraps of meat.  ‘Stone soup,’ thus made, was a very satisfactory soup.  He said that in practically all of the tests of raw phosphate conducted by the various State Experiment Stations, manure has been used as a means of supplying organic matter to liberate the phosphorus from the raw rock, but in such large quantity as to be entirely impracticable for the average farmer to use on his own fields; and his opinion was that the entire benefit was due to the manure.  He had a little booklet entitled ‘Available or Unavailable Plant Food—­Which?’ published by the National Fertilizer Association, and said I could get a copy by addressing the Secretary at Nashville, Tennessee.”

“Fortunately,” said Percy, “this is not a question of opinion but one of fact; and it has been discovered that the fertilizer agents who are long on opinions and short on facts prefer to sell four tons of complete fertilizer for $80, or even two tons of acid phosphate for $30, rather than to sell one ton of raw phosphate, containing the same amount of phosphorus, for $7.50.  In the manufacture of acidulated fertilizers, one ton of raw phosphate, containing about two hundred and fifty pounds of the element phosphorus, is mixed with one ton of sulfuric acid to make two tons of acid phosphate; and, as a rule, these two tons of acid phosphate are mixed with two tons of filler to make four tons of complete fertilizer.  A favorite filler is dried peat, which is taken from some of the peat bogs, as at Manito, Illinois, and shipped in train loads to the fertilizer factories.  The peat is not considered worth hauling onto the land in Illinois, even where the farmers can get it for nothing; but it contains some organic nitrogen, and, by the addition of a little potassium salt, the agent is enabled to call the product a ‘complete’ fertilizer.