“Now let me finish,” Percy continued, when Mr. Thornton had somewhat subsided.  “I say, if I am permitted to separate Miss Russell and the Thorntons from about three hundred acres of their land, I shall certainly wish to know its total content of phosphorus, potassium, magnesium, and calcium, before I make any purchase; and, if you will remember the pot cultures and the peaty swamp land, I think you’d agree with me.

“Well, I shall be mighty glad to know that myself,” said Mr. Thornton, “and we shall much appreciate it if you can tell us how to secure that information.”

“We can collect some soil to-morrow,” Percy replied, “and send it to a chemist for analysis.”

“Good,” said Mr. Thornton; “now just one more question, and I think I shall sleep better if I have it answered to-night.  Just what is meant by potash and phosphoric acid?”

“Potash,” said Percy, “is a compound of potassium and oxygen.  The proportions are one atom of oxygen and two atoms of potassium, which you may remember are single-handed and weigh thirty-nine, so that seventy-eight of potassium unite with sixteen of oxygen.  A better name for the compound is potassium oxid:  K20.  The Latin name for potassium is kalium, and K is the symbol used for an atom of that element.  If you were to purchase potassium in the form of potassium chlorid, which in the East is often called by the old incorrect name ‘muriate of potash,’ the salt might be guaranteed to contain a certain percentage of potash, which, however, consists of eighty-three per cent. of potassium and seventeen of oxygen.”

“Just what is this potassium chlorid, or ’muriate of potash’?”

“Pure potassium chlorid contains only the two elements, potassium and chlorin.”

“But didn’t you say that it was guaranteed to contain potash and that potash is part oxygen?  Now you say it contains only potassium and chlorin.”

“Yes, I am sorry to say, that this is one of those blunders of our semi-scientific ancestors for which we still suffer.  The chemist understands that the meaning of the guarantee of potash is the amount of potash that the potassium present in the potassium chlorid could be converted into.  The best you can do is to reduce the potash guarantee to potassium by taking eighty-three per cent. of it; or, to be more exact, divide by ninety-four and multiply by seventy-eight, in order to eliminate the sixteen parts of oxygen.

“It may be well to keep in mind that when the druggist says potash he means potassium hydroxid, Koh, a compound of potassium, hydrogen, and oxygen, as the name indicates.”

“You mentioned the word chlorin,” said Mr. Thornton.  “That is another element?”

“Yes, that is a very common element.  Ordinary table salt is sodium chlorid:  NaCl.  Sodium is called natrium in Latin, and Na is the symbol used in English to be in harmony with all other languages, for practically all use the same chemical symbols.  Sodium and potassium are very similar elements in some respects, and in the free state they are very peculiar, apparently taking fire when thrown into water.  Chlorin in the free state is a poisonous gas.  Thus the change in properties is well illustrated when these two dangerous elements, sodium and chlorin, unite to form the harmless compound which we call common salt.