The Story of the Soil Part 14

"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 pota.s.sium present in the pota.s.sium chlorid could be converted into. The best you can do is to reduce the potash guarantee to pota.s.sium 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 pota.s.sium hydroxid, KOH, a compound of pota.s.sium, 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 pota.s.sium 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 ill.u.s.trated when these two dangerous elements, sodium and chlorin, unite to form the harmless compound which we call common salt.

"It is a shame," continued Percy, "that agricultural science has so long been burdened with such a term as 'phosphoric acid,' which serves to complicate and confuse what should be made the simplest subject to every American farmer and landowner. As agriculture is the fundamental support of America and of all her other great industries, so the fertility of the soil is the absolute support of every form of agriculture. Now, if there is any one factor that can be the most important, where so many are positively essential, then the most important factor in the problem of adopting and maintaining permanent systems of profitable agriculture on American soils is the element phosphorus.

"Phosphorus in very appreciable amount is positively necessary for the growth of every organism. It is an absolutely essential const.i.tuent of the nucleus of every living cell, whether plant or animal. Nuclein, itself, which is the substance nearest to the beginning of a new cell, contains as high as ten per cent. of the element phosphorus.

"On the other hand, phosphorus is the most limited of all the plant food elements, measured by supply and demand and circulation.

"What is phosphoric acid? Well, the professor of chemistry says it is a compound containing three atoms of hydrogen, one of phosphorus, and four of oxygen. It is a syrupy liquid and one of the strongest mineral acids. In concentrated form it is as caustic as oil of vitriol. Why, here you have a Century dictionary. That should tell what phosphoric acid is. This is what the Century says:

"'It is a colorless, odorless syrup, with an intensely sour taste.

It is tribasic, forming three distinct cla.s.ses of metallic salts.

The three atoms of hydrogen may in like manner be replaced by alcohol radicles, forming acid and neutral ethers. Phosphoric acid is used in medicine as a tonic.'

"That," continued Percy, "is the complete definition as given by the Century dictionary as to what phosphoric acid is, and I note that this is the latest edition of the Century, copyrighted in 1902."

"We bought it less than a month ago," said Mrs. Thornton. "We can have so few books that we thought the Century would be a pretty good library in itself; Mr. Thornton has had too little time to use it much as yet."

"Well, even if I had used it," said Mr. Thornton, "you see there are five volumes before I'd get to the P's. But, joking aside, I don't get much out of that definition except that phosphoric acid is a sour liquid and is used in medicine."

"The definition is entirely correct," said Percy "Any text on chemistry will give you a very similar definition, and your physician and druggist will give you the same information."

"Well, I know the fertilizer agents claim to sell phosphoric acid in two-hundred-pound bags which wouldn't hold any kind of liquid."

"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' inst.i.tutes 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 a.n.a.lyses of soils and fertilizers on the basis of nitrogen instead of ammonia; and in the Corn Belt States, phosphorus and pota.s.sium are the terms used to a large extent instead of 'phosphoric acid,' and potash. The agricultural press is greatly a.s.sisting 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 pota.s.sium, 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.

"As stated in your Century dictionary, true phosphoric acid forms three distinct cla.s.ses of salts, because either one, two, or all of the three hydrogen atoms may be replaced by a metallic element.

Thus, we have phosphoric acid itself containing the three hydrogen atoms, one phosphorus atom, and four oxygen atoms. This might be called trihydrogen phosphate (H3PO4). Now if one of the hydrogen atoms is replaced by one pota.s.sium atom, we have pota.s.sium dihydrogen phosphate (KH2PO4); with two pota.s.sium atoms and one hydrogen, we have dipota.s.sium hydrogen phosphate (K2HPO4); and if all hydrogen is replaced by pota.s.sium the compound is tripota.s.sium phosphate (K3PO4). To make similar salts with two-handed metallic elements, like calcium or magnesium, we need to start with two molecules of phosphoric acid H6(PO4)2; because each atom of calcium will replace two hydrogen atoms. Thus we have mono calcium phosphate, CaH4(PO4)2, dicalcium phosphate, Ca2H2(PO4)2, and tricalcium phosphate, Ca3(PO4)2. It goes without saying that monocalcium phosphate contains four atoms of hydrogen and that dicalcium phosphate contains two hydrogen atoms. By knowing the atomic weights (40 for calcium, 31 for phosphorus, and 16 for oxygen), it is easy to compute that the molecule of tricalcium phosphate weighs 310 of which 62 is phosphorus. This is exactly one-fifth, or twenty per cent. This compound you will remember is sometimes called 'bone phosphate of lime'. It is also called simply 'bone phosphate'; because it is the phosphorus compound contained in bones. It is sometimes called lime phosphate, although it contains no lime in the true sense, for it has no power to neutralize acid soils, except when the phosphorus is taken up by plants more rapidly than the calcium, which in such case might remain in the soil to act as a base to neutralize soil acids; but even then the effect of the small amount of calcium thus liberated from the phosphate would be very insignificant compared with a liberal application of ground limestone."

"Well," said Mr. Thornton, stretching himself, "orange phosphate is my favorite drink but I fear some of these phosphate you have just been giving me are too concentrated. I ought to have the dose diluted; but I like the taste of it, and if you'll write a book along this line, in this plain way just about as you have been giving it to me straight for almost twelve hours, I tell you I'll read it over till I learn to understand it a heap better than I do now."

CHAPTER XVIII

CLOSER TO MOTHER EARTH

THE following day Percy collected soil samples to represent the common type of soil on the farm. In the main the land was nearly level and very uniform, although here and there were small areas which varied from the main type, and in places the variation was marked. Percy and his host devoted the entire day to an examination of the soils of the farm and the collection of the samples.

"The prevailing soil type is what would be called a loam," said Percy, "and a single set of composite samples will fairly represent at least three-fourths of the land on this farm.

"It seems to me that it is enough for the present to sample this prevailing type, and later, if you desire, you could collect samples of the minor types, of which there are at least three that are quite distinct."

"A loam soil is one that includes a fair proportion of the several groups of soil materials, including silt, clay, and sand."

"What is silt?" asked Mr. Thornton.

"Silt consists of the soil particles which are finer than sand,--too small in fact to be felt as soil grains by rubbing between the fingers, and yet it is distinctly granular, while clay is a mere plastic or sticky ma.s.s like dough. What are commonly called clay soils consist largely of silt, but contain enough true clay to bind the silt into a stiff ma.s.s. In the main such soils are silt loams, but when deficient in organic matter they are yellow in color as a rule, and all such material is usually called clay by the farmers."

"Well, I had no idea that it would take us a whole day to get enough dirt for an a.n.a.lysis," remarked Mr. Thornton, as they were collecting the samples late in the afternoon. "Five minutes would have been plenty of time for me, before I saw the holes you've bored to-day."

"The fact is," replied Percy, "that the most difficult work of the soil investigator is to collect the samples. Of course any one could fill these little bags with soil in five minutes, but the question is, what would the soil represent? It may represent little more than the hole it came out of, as would be the case where the soil had been disturbed by burrowing animals, or modified by surface acc.u.mulations, as where a stack may sometime have been burned. In the one case the subsoil may have been brought up and mixed with the surface, and in the other the mineral const.i.tuents taken from forty acres in a crop of clover may have been returned to one-tenth of an acre."

"Certainly such things have occurred on many farms," agreed Mr.

Thornton, "and they may have occurred on this farm for all any one knows."

"Fifty tons of clover hay," continued Percy, after making a few computations, "would contain 400 pounds of phosphorus, 2400 pounds of pota.s.sium, 620 pounds of magnesium, and 2340 pounds of calcium."

"I don't see how you keep all those figures in your head," said Mr.

Johnston.

"How many pounds are there in a ton of hay?" asked Percy.

"Two thousand."

"How many pounds in a bushel of oats?"

"Thirty in Virginia, but thirty-two in Carolina."

"How many in a bushel of wheat?"