Chapter 75

BONE-DUST AND SUPERPHOSPHATE OF LIME.

Bone-dust is often spoken of as a phosphatic manure, and it has been supposed that the astonishing effect bone-dust sometimes produces on old pasture-land, is due to its furnishing phosphoric acid to the soil.

But it must be remembered that bone-dust furnishes nitrogen as well as phosphoric acid, and we are not warranted in ascribing the good effect of bones to phosphoric acid alone.

Bones differ considerably in composition. They consist essentially of gelatine and phosphate of lime. Bones from young animals, and the soft porous parts of all bones, contain more gelatine than the solid parts, or the bones from older animals. On the average, 1,000 lbs. of good commercial bone-dust contains 38 lbs. of nitrogen.

On the old dairy farms of Cheshire, where bone-dust produced such marked improvement in the quantity and quality of the pastures and meadows, it was usual to apply from 4,000 to 5,000 lbs. per acre, and often more. In other words, a dressing of bone-dust frequently contained 200 lbs. of nitrogen per acre--equal to 20 or 25 tons of barn-yard manure.

“It has been supposed,” said the Doctor, “that owing to the removal of so much phosphoric acid in the cheese sold from the farm, that the dairy pastures of Cheshire had been exhausted of phosphoric acid, and that the wonderful benefits following an application of bone-dust to these pastures, was due to its supplying phosphoric acid.”

“I do not doubt,” said I, “the value of phosphoric acid when applied in connection with nitrogen to old pasture lands, but I contend that the experience of the Cheshire dairymen with bone-dust is no positive proof that their soils were particularly deficient in phosphoric acid. There are many instances given where the gelatine of the bones, alone, proved of great value to the grass. And I think it will be found that the Cheshire dairymen do not find as much benefit from superphosphate as they did from bone-dust. And the reason is, that the latter, in addition to the phosphoric acid, furnished a liberal dressing of nitrogen. Furthermore, it is not true that dairying specially robs the soil of phosphoric acid. Take one of these old dairy farms in Cheshire, where a dressing of bone-dust, according to a writer in the Journal of the Royal Agricultural Society, has caused ‘a miserable covering of pink grass, rushes, and a variety of other noxious weeds, to give place to the most luxuriant herbage of wild clover, trefoil, and other succulent and nutritious grasses.’ It is evident from this description of the pastures before the bones were used, that it would take at least three acres to keep a cow for a year.”

“I have known,” says the same writer quoted above, “many a poor, honest, but half broken-hearted man raised from poverty to comparative independence, and many a sinking family saved from inevitable ruin by the help of this wonderful manure.” And this writer not only spoke from observation and experience, but he showed his faith by his works, for he tells us that he had paid nearly $50,000 for this manure.

Now, on one of these poor dairy farms, where it required 3 acres to keep a cow, and where the grass was of poor quality, it is not probable that the cows produced over 250 lbs. of cheese in a year. One thousand pounds of cheese contains, on the average, about 45½ lbs. of nitrogen; 2½ lbs. of potash, and 11½ lbs. of phosphoric acid. From this it follows, if 250 lbs. of cheese are sold annually from three acres of pasture, less than one lb. of phosphoric acid per acre is exported from the farm in the cheese.

One ton of timothy-hay contains nearly 14½ lbs. of phosphoric acid. And so a farmer who raises a ton of timothy-hay per acre, and sells it, sends off as much phosphoric acid in one year as such a Cheshire dairyman as I have alluded to did in fourteen years.

What the dairymen want, and what farmers generally want, is nitrogen _and_ phosphoric acid. Bone-dust furnishes both, and this was the reason of its wonderful effects.

It does not follow from this, that bone-dust is the cheapest and best manure we can use. It is an old and popular manure, and usually commands a good price. It sells for all it is worth. A dozen years ago, I bought ten tons of bone-dust at $18 per ton. I have offered $25 per ton since for a similar lot, but the manufacturers find a market in New York for all they can make.

Bone-dust, besides nitrogen, contains about 23 per cent of phosphoric acid.

“That does not give me,” said the Deacon, “any idea of its value.”

“Let us put it in another shape, then,” said I. “One ton of good bone-dust contains about as much nitrogen as 8½ tons of fresh stable-manure, and as much phosphoric acid as 110 tons of fresh stable-manure. But one ton of manure contains more potash than 5 tons of bone-dust.”

Bone-dust, like barnyard-manure, does not immediately yield up its nitrogen and phosphoric acid to plants. The bone phosphate of lime is insoluble in water, and but very slightly soluble in water containing carbonic acid. The gelatine of the bones would soon decompose in a moist, porous, warm soil, provided it was not protected by the oil and by the hard matter of the bones. Steaming, by removing the oil, removes one of the hindrances to decomposition. Reducing the bones as fine as possible is another means of increasing their availability.

Another good method of increasing the availability of bone-dust is to mix it with barnyard-manure, and let both ferment together in a heap. I am inclined to think this the best, simplest, and most economical method of rendering bone-dust available. The bone-dust causes the heap of manure to ferment more readily, and the fermentation of the manure softens the bones. Both the manure and the bones are improved and rendered richer and more available by the process.

Another method of increasing the availability of bone-dust is by mixing it with sulphuric acid.

The phosphate of lime in bones is insoluble in water, though rain water containing carbonic acid, and the water in soils, slowly dissolve it. By treating the bones with sulphuric acid, the phosphate of lime is decomposed and rendered soluble. Consequently, bone-dust treated with sulphuric acid will act much more rapidly than ordinary bone-dust. The sulphuric acid does not make it any _richer_ in phosphoric acid or nitrogen. It simply renders them more available.

“And yet,” said the Doctor, “the use of sulphuric acid for ‘dissolving’ bones, or rather phosphate of lime, introduced a new era in agriculture. It is the grand agricultural fact of the nineteenth century.”

“It is perhaps not necessary,” said I, “to give any direction for treating bones with sulphuric acid. We have got beyond that. We can now buy superphosphate cheaper than we can make it from bones.”

“But is it as good?” asked the Deacon.

“Soluble phosphate of lime,” said I, “is soluble phosphate of lime, and it makes no difference whether it is made from burnt bones, or from phosphatic guano, or mineral phosphate. That question has been fully decided by the most satisfactory experiments.”

“Before you and the Deacon discuss that subject,” said the Doctor, “it would be well to tell Charley what superphosphate is.”

“I wish you would tell me,” said Charley.

“Well,” said the Doctor, “phosphate of lime, as it exists in bones, is composed of three atoms of lime and one atom of phosphoric acid. Chemists call it the tricalcic phosphate. It is also called the basic phosphate of lime, and not unfrequently the ‘bone-earth phosphate.’ It is the ordinary or common form of phosphate of lime, as it exists in animals, and plants, and in the various forms of mineral phosphates.

“Then there is another phosphate of lime, called the dicalcic phosphate, or neutral phosphate of lime, or reverted phosphate of lime. It is composed of one atom of water, two atoms of lime, and one atom of phosphoric acid.

“Then we have what we call superphosphate, or acid phosphate of lime, or more properly monocalcic phosphate. It is composed of two atoms of water, one atom of lime, and one atom of phosphoric acid. This acid phosphate of lime _is soluble in water_.

“The manufacture of superphosphate of lime is based on these facts. The _one-lime_ phosphate is soluble, the _three-lime_ phosphate is insoluble. To convert the latter into the former, all we have to do is to _take away two atoms of lime_.

“Sulphuric acid has a stronger affinity for lime than phosphoric acid. And when you mix enough sulphuric acid with finely ground three-lime phosphate, to take away two atoms of lime, you get the phosphoric acid united with one atom of lime and two atoms of water.”

“And what,” asked the Deacon, “becomes of the two atoms of lime?”

“They unite with the sulphuric acid,” said the Doctor, “and form plaster, gypsum, or sulphate of lime.”

“The molecular weight of water,” continued the Doctor, “is 18; of lime, 56; of sulphuric acid, 80; of phosphoric acid, 142.

“An average sample of commercial bone dust,” continued the Doctor, “contains about 50 per cent of phosphate of lime. If we take 620 lbs. of finely-ground bone-dust, containing 310 lbs. of three-lime phosphate, and mix with it 160 lbs. of sulphuric acid (say 240 lbs. common oil of vitriol, sp. gr. 1.7), the sulphuric acid will unite with 112 lbs. of lime, and leave the 142 lbs. of phosphoric acid united with the remaining 56 lbs. of lime.”

“And that will give you,” said the Deacon, “780 lbs. of ‘dissolved bones,’ or superphosphate of lime.”

“It will give you more than that,” said the Doctor, “because, as I said before, the two atoms of lime (112 lbs.) are replaced by two atoms (36 lbs.) of water. And, furthermore, the two atoms of sulphate of lime produced, contained two atoms (36 lbs.) of water. The mixture, therefore, contains, even when perfectly dry, 72 lbs. of water.”

“Where does this water come from?” asked the Deacon.

“When I was at Rothamsted,” said I, “the superphosphate which Mr. Lawes used in his experiments was made on the farm from animal charcoal, or burnt bones, ground as fine as possible--the finer the better. We took 40 lbs. of the meal, and mixed it with 20 lbs. of water, and then poured on 30 lbs. of common sulphuric acid (sp.g. 1.7), and stirred it up rapidly and thoroughly, and then threw it out of the vessel into a heap, on the earth-floor in the barn. Then mixed another portion, and so on, until we had the desired quantity, say two or three tons. The last year I was at Rothamsted, we mixed 40 lbs. bone-meal, 30 lbs. water, and 30 lbs. acid; and we thought the additional water enabled us to mix the acid and meal together easier and better.”

“Dr. Habirshaw tells me,” said the Doctor, “that in making the ‘Rectified Peruvian Guano’ no water is necessary, and none is used. The water in the guano and in the acid is sufficient to furnish the two atoms of water for the phosphate, and the two atoms for the sulphate of lime.”

“Such is undoubtedly the case,” said I, “and when large quantities of superphosphate are made, and the mixing is done by machinery, it is not necessary to use water. The advantage of using water is in the greater ease of mixing.”

“Bone-dust,” said the Doctor, “contains about 6 per cent of water, and the sulphuric acid (sp.g. 1.7) contains about one-third its weight of water. So that, if you take 620 lbs. of bone-dust, and mix with it 240 lbs. of common sulphuric acid, you have in the mixture 117 lbs. of water, which is 45 lbs. more than is needed to furnish the water of combination.”

“The superphosphate produced from 620 lbs. of bones, therefore,” continued the Doctor, “would contain:

Phosphoric acid} {142 lbs. Lime } acid phosphate { 56 ” Water } { 36 ”

Sulphuric acid } {160 lbs. Lime } sulphate of lime {112 ” Water } { 36 ”

Organic matter, ash, etc., of the bones* 335 ” -------- Total _dry_ superphosphate 877 ” Moisture, or loss 45 ” -------- Total mixture 922 lbs.

* Containing nitrogen, 23½ lbs.

“There is a small quantity of carbonate of lime in the bones,” said I, “which would take up a little of the acid, and you will have a remarkably good article if you calculate that the 620 lbs. of bone-dust furnish you half a ton (1,000 lbs.) of superphosphate. It will be a better article than it is practically possible to make.”

“Assuming that it made half a ton,” said the Doctor, “it would contain 14¼ per cent of soluble phosphoric acid, and 2⅓ per cent of nitrogen.”

“With nitrogen at 20 cents per lb., and soluble phosphoric acid at 12½ c. per lb., this half ton of superphosphate, made from 620 lbs. of good bone-dust, would be worth $22.50, or $45 per ton.”

“Or, to look at it in another light,” continued the Doctor, “a ton of bone-dust, made into such a superphosphate as we are talking about, would be worth $72.58.”

“How much,” asked the Deacon, “would a ton of the bone-dust be considered worth before it was converted into superphosphate?”

“A ton of bone-dust,” replied the Doctor, “contains 76 lbs. of nitrogen, worth, at 18 cents per lb., $13.68, and 464 lbs. phosphoric acid, worth 7 cents per lb., $32.48. In other words, a ton of bone-dust, at the usual estimate, is worth $46.16.”

“And,” said the Deacon, “after it is converted into superphosphate, the same ton of bones is worth $72.58. It thus appears that you pay $26.42 per ton for simply making the phosphoric acid in a ton of bones soluble. Isn’t it paying a little too much for the whistle?”

“Possibly such is the case,” said I, “and in point of fact, I think bone-dust, especially from steamed or boiled bones, can be used with more economy in its natural state than in the form of superphosphate.”

Superphosphate can be made more economically from mineral phosphates than from bones--the nitrogen, if desired, being supplied from fish-scrap or from some other cheap source of nitrogen.

But for my own use I would prefer to buy a good article of superphosphate of lime, containing no nitrogen, provided it can be obtained cheap enough. I would buy the ammoniacal, or nitrogenous manure separately, and do my own mixing--unless the mixture could be bought at a less cost than the same weight of soluble phosphoric acid, and available nitrogen could be obtained separately.

A pure superphosphate--and by pure I mean a superphosphate containing no nitrogen--can be drilled in with the seed without injury, but I should be a little afraid of drilling in some of the ammoniacal or nitrogenous superphosphates with small seeds.

And then, again, the “nitrogen” in a superphosphate mixture may be in the form of nitric acid, or sulphate of ammonia, in one case, or, in another case, in the form of hair, woollen rags, hide, or leather. It is far more valuable as nitric acid or ammonia, because it will act quicker, and if I wanted hair, woollen rags, horn-shavings, etc., I would prefer to have them separate from the superphosphate.