“True,” replied Percy, “and I consider it a shame that the farm boy who goes to the high school or college and is there taught exactly what phosphoric acid is, must. when he returns to the farm, try to read bulletins from his agricultural experiment station in which the term ‘phosphoric acid’ is used for what it is not.  At the state agricultural college, the professor of chemistry correctly teaches the farm boy that phosphoric acid is a liquid compound containing three atoms of hydrogen, one of phosphorus, and four of oxygen in the molecule; and then the same professor, as an experiment station investigator, goes to the farmers’ institutes and incorrectly teaches the same boy’s father that phosphoric acid is a solid compound pound containing two atoms of phosphorus and five atoms of oxygen in the molecule.”

“But why do they continue to teach such confusion?”

“Well, Sir, if they know, they never tell.  In some manner this misuse of the name was begun, and every year doubles the difficulty of stopping it.”

“Like the man that was too lazy to stop work when he had once begun,” remarked Mr. Thornton.

“Yes,” said Percy, “but it is true that some of the States have adopted the practice of reporting analyses of soils and fertilizers on the basis of nitrogen instead of ammonia; and in the Corn Belt States, phosphorus and potassium are the terms used to a large extent instead of ‘phosphoric acid,’ and potash.  The agricultural press is greatly assisting in bringing about the adoption of the simpler system, and the laws of some States now require that the percentages of the actual plant food elements, as nitrogen, phosphorus, and potassium, shall be guaranteed in fertilizers offered for sale.  It is one of those questions that are never settled until they are settled right; and it is only a question of time until the simple element basis will be used throughout the United States, or at least in the Central and Western States.”

“The so-called ‘phosphoric acid’ of the fertilizer agent is a compound whose molecule contains two atoms of phosphorus and five atoms of oxygen; and, since the atomic weight of phosphorus is thirty-one and that of oxygen sixteen, this compound contains sixty-two parts of phosphorus and eighty parts of oxygen.  In other words, this phosphoric acid, falsely so-called, contains a trifle less than forty-four per cent. of the actual element phosphorus.”

“Is the bone phosphate of lime that the agents talk about the same as the ’phosphoric acid’?” asked Mr. Thornton.

“No, by ‘bone phosphate of lime,’ which is often abbreviated B. P. L., is meant tricalcium phosphate, a compound which contains exactly twenty per cent. of phosphorus.  Thus, you can always divide the guaranteed percentage of ‘bone phosphate of lime’ by five, and the result will be the per cent. of phosphorus.