LIME HYDRATE

_Slaking Lime._ The usual means of reducing fresh burned stone lime to a condition that makes even distribution upon land possible is by slaking.

A few years ago considerable effort was made to create a market for lime pulverized by machinery, but the difficulty in excluding the moisture of the air so that packages would not burst has been in the way of developing a market. Slaking, by the addition of water to the fresh burned lime, is the common method of getting the required physical condition. When the slaking is done on the farm, the custom has been to distribute the lime in small piles in the field, placing the piles at such convenient distance apart that the lime, after slaking, could be spread easily with a shovel.

The water for slaking comes from rains, or from moisture in the air and earth. The method is wasteful and can be justified, if ever, only where farm-burned lime costs little per ton, and the nature of the soil is such that a relatively heavy application can be safely made. The distribution is necessarily uneven, and if the required amount goes upon all the surface, a great excess is sure to go upon a portion of it. Very often an excess of water puddles much of the lime in the pile, and lumps may be seen lying in ineffective form in the soil for years. The practice is responsible for much of the excessive application that brought the use of caustic lime into disrepute.

_Slaking in Large Heaps._ A preferable method is to put the lime in flat heaps of large size and about four feet deep, so that water may be applied or advantage be taken of rainfall. The value of the lime is so great that one can well afford to draw water and apply with a hose so that the quant.i.ty can be controlled with exactness. When fresh burned lime is perfectly slaked, each 56 pounds of pure lime becomes 74 pounds of hydrated lime, water furnis.h.i.+ng the added weight.

_Hydrated Lime on the Market._ A popular form of lime on the market is the hydrate. Manufacturers first burn the stone, and in the case of a pure limestone they drive off 44 pounds of each 100 pounds of the weight in burning. Then, they combine enough water with the lime to change it to hydrate form, and that adds 18 pounds weight. It is run through a sieve to remove any coa.r.s.e material, and then packed in bags which help to exclude the air. The small packages in which it comes upon the market make handling easy, and this helps to bring it into demand.

Its good physical condition makes even distribution possible, and thus permits maximum effectiveness to be obtained. It is only slaked lime, identical in composition and value with lime of the same purity slaked on the farm, but some dealers have been able to create the impression that it has some added quality and peculiar power. This does no credit to the public intelligence, but the hunger of soils for lime is so great that investment at a price wholly out of proportion to the price of farm-slaked lime has rarely failed to yield some profit.

_Degree of Purity._ It is always a reasonable a.s.sumption that hydrated lime has been made from stone of a good degree of purity. A local stone, burned on the farm, may be of low grade, but no man of business judgment would erect a costly plant for burning and hydrating lime where the purity of the stone would not afford a good advertis.e.m.e.nt in itself.

On the other hand, we find very little hydrated lime on the market that has not had sufficient exposure to the air to become changed in some part to an air-slaked condition, or has had refuse mixed with it.

Air-slaked lime is not worth as much per ton as the hydrate because it cannot correct as much soil acidity, and the percentage of the former cannot be determined by the buyer. Its presence may not be due to any wrong-doing of the manufacturer, and, on the other hand, the increase in weight that attends air-slaking may be welcomed in some degree by a dishonest manufacturer before the goods are s.h.i.+pped. The difficulty in preventing hydrated lime from adding to its weight by becoming air-slaked is a point to be taken into consideration.

The percentages of air-slaked material in hydrated limes are widely variable, and no manufacturer can standardize his product on the market surely for the benefit of the farmer. In some instances the product is adulterated with refuse material in finely pulverized condition.

CHAPTER XIII

OTHER FORMS OF LIME

_Air-Slaked Lime._ A pure limestone is a carbonate, and the chemical formula is CaCO_3. When it is burned, the carbon dioxide (CO_2) is driven off, leaving CaO, which is calcium oxide, called fresh burned lime. In this process 44 pounds of a stone weighing 100 pounds pa.s.ses into the air, and there remain 56 pounds of lime. When it air-slakes, it takes back the carbon dioxide from the air, and the new product becomes CaCO3, or carbonate of lime, and regains its original weight of 100 pounds. This is what would happen if the process were complete, and it is nearly so when the exposure to the air is as perfect as possible.

Fifty-six pounds of valuable material are in the 100 pounds of air-slaked lime, just as is the case with limestone, and there is no difference in effectiveness except in so far as the air-slaked material is absolutely fine and available, while most pulverized limestone is less so. In making purchase for use of land the buyer cannot afford to make any appreciable difference in price in favor of air-slaked lime, as compared with a fine stone.

_Air-Slaking a Slow Process._ Lime changes to an air-slaked condition slowly unless it has full exposure. Old heaps will remain in hydrate form for many years, excepting the outside coat, which excludes the air.

Complete air-slaking would not reduce ability to correct soil acidity, the total amount of calcium and magnesium remaining constant, but weight would be added in the slaking, and therefore the value per ton would be reduced. The slowness with which air-slaking proceeds gives reason to expect that any bulk of old lime may contain a considerable percentage of the hydrate, and therefore have greater strength than a true carbonate like limestone. This is a consideration of value to a buyer.

_Agricultural Lime._ Some manufacturers have found in the demand for lime by farmers an opportunity of disposing of much material that would not be satisfactory to manufacturers and builders. In some cases this so-called agricultural lime is sold at a price that is not beyond value, but it varies much in its content of pure lime. If the unburned cores of kilns are ground up, the material simply retains the value of unburned stone. Any air-slaked material put into it has like value.

Forkings, ground up, have less value, and sometimes no value at all.

Some better material may go into this mixture that is given the name "agricultural lime," and the product cannot be standardized or have a valuation given it that would be true for another lot.

Some manufacturers are marketing limes of fair values under this designation, but the values change as the material changes. There are other manufacturers who are putting poor stuff on the market. Unless one knows the manufacturer and his processes, he should not pay a great deal for "agricultural lime." It is much better to buy a high-grade lime or limestone that is more nearly constant in composition. When the word "agricultural" is part of the brand, there is a.s.surance that the percentage of waste stuff in it is relatively high. Unless one knows to the contrary, he should a.s.sume that a ton of finely pulverized limestone is worth more per ton than "agricultural lime."

_Marl._ Marls vary in composition, as limestones do, but there are beds of chalky marl that contain very little clay and sand and are nearly a pure carbonate. It is only marls of high degree of purity that can be put on the market with profit, but beds of less pure marl furnish dressings for farms of the locality in many sections of the country.

Some of these inferior marls have had so much clay and sand mixed with the lime carbonate that dressings must be heavy. The best lime marls provide excellent material for the correction of soil acidity, the actual value per ton being practically the same as that of the finest pulverized limestone. Some dealers in marl make extravagant claims for their goods, but any farmer may easily put these claims to the test and learn that he should not expect more than a fairly good carbonate of lime can do.

Marl improves the physical condition of stiff soils only when used in large amount per acre, and this is true of any carbonate form, such as limestone. Little effect upon physical condition should be expected from the light application usually given when marl is purchased and transported some distance to the farm. The chalk marl on the market is used to correct soil acidity, and at the best it is worth only what good lime carbonate is worth. It has no hidden virtues, and cannot take the place of fertilizers. It is an excellent means of meeting the lime-requirement of land when bought right, and its fine division makes it distinctly superior to coa.r.s.e stone.

There should be no confusion of a lime marl with the so-called "green sand" marl. The latter is low in lime, and may be acid, the value of the marl being in a considerable percentage of plant food contained.

_Oyster Sh.e.l.l._ Ground oyster sh.e.l.l is a good source of carbonate of lime. The percentage falls below that of limestone, but in addition there is a little nitrogen and phosphoric acid. An a.n.a.lysis of a good quality of oyster sh.e.l.l, as found on the market, will show 90% carbonate of lime.

Burned oyster sh.e.l.l has something near the same composition as lime made from stone, but it goes back to hydrate and air-slaked forms rapidly.

There is no large amount of burned sh.e.l.l lime on the market, the material known as sh.e.l.l lime being the ground sh.e.l.l, or lime carbonate.

_Wood Ashes._ A large supply of lime in excellent form was afforded by hardwood ashes, but this product has ceased to have any important value to our agriculture. The chief supply on the market is low in quality, containing moisture and dirt in considerable amount, the form of lime being changed from an oxide to the hydrate and carbonate.

_Gas Lime._ Prof. E. B. Voorhees, in "First Principles of Agriculture,"

says: "Gas lime is also frequently used as manure; in gas works, quicklime is used for removing the impurities from the gas. Gas lime, therefore, varies considerably in composition, and consists really of a mixture of slaked lime, or calcium hydrate, and carbonate of lime, together with sulfites and sulfides of lime. These last are injurious to young plant life, and gas lime should be applied long before the crop is planted, or at least exposed to the air some time before its application. The action of air converts the poisonous substances in it into non-injurious products. Gas lime contains on an average 40% of calcium oxide, and usually a small percentage of nitrogen."

_Lime After Magnesium Removal._ A by-product in the removal of magnesium from a magnesian limestone is an excellent material for correction of soil acidity, on account of its physical condition. Its exposure to the air causes much of the hydrate to change to an air-slaked form, and its value per ton lies somewhere between that of very finely pulverized limestone and hydrated lime.

CHAPTER XIV

MAGNESIAN LIME

_Magnesium._ As an element of plant food, magnesium is as essential as calcium. It leaches out of the soil less readily, and there may be even less need of its application as a plant food, though the need of calcium applications for this purpose is a.s.sumed to be small. In the correction of soil acidity magnesium is more effective than calcium, 84 pounds of the carbonate being equal to 100 pounds of calcium carbonate. It is a curious fact, however, that there is widespread fear of magnesium as a soil amendment. This is not traceable to any considerable experience by practical farmers that inspires caution in its use, although immense quant.i.ties of magnesian limestone and lime have been used. Neither is it due to any weight of evidence against it in the experience or teachings of soil chemists and experiments. The facts of the case appear to be as follows:

1. An investigator found in his laboratory that a plant growing in a water solution was injured when magnesium was added, and that the injury was checked when calcium in equal amount was added to the water.

The theory was worked out that a soil should not contain a greater total amount of magnesium than of calcium, and as the soil's supply of calcium tends to leach out more readily than the supply of magnesium, it was best to use a high-calcium lime. If this discovery of the laboratory had been carried into the field, its significance would have dwindled to zero in the case of normal soils, and a lot of exploitation would have been rendered impossible. As it was, the discussion went merrily along until it occurred to some one to test the matter in the soils where plants grow, and one would now hear little of it if commercial interests were not at stake.

2. Very much of our limestone supply is high in magnesium, and some men who have limestone very low in magnesium and high in calcium have done a good stroke of business for themselves by deepening the public's impression, due to laboratory tests with water cultures, that magnesium in lime is injurious.

3. Many people knew "lime," but had no knowledge of magnesia, and if it was an impurity like clay or sand, cutting down value per ton, and if it was worse because harmful, they wanted none of it.

_The Fact's Importance._ If every farm could get its supply of pure calcium lime as cheaply as it can have magnesian lime, the truth respecting the value of the latter would have small agricultural importance, but as a great bulk of farm and commercial supplies of lime is magnesian, financial injury has been done consumers who have paid more than should have been paid for relatively pure calcium lime and limestone, being afraid to use goods whose content of magnesium was not small. It is poor policy to use either kind of burned lime in great excess, but when rationally used on all soils except sandy ones, there is no preference to be exercised that can be based upon performance. A magnesian lime corrects as much acidity as a high calcium lime, and a little more, and its use is to be recommended if there is any advantage in the matter of price, except in the case of distinctly sandy soils.

_Magnesian Limestone._ Leading scientists making tests of limestone for normal soils, use magnesian limestone freely. They recommend its use to farmers wherever there is advantage in point of price. The advice is safe that the limestone of a given fineness should be chosen whose total percentage of carbonates of calcium and magnesium is the highest. The example of these scientists, buying pulverized limestone for agricultural colleges and experiment farms, and for their own farms, should loosen the curious hold that the early warnings of a laboratory experimenter took upon public imagination. The farmer should buy limestone on a basis of ability to correct soil acidity, and make each dollar do the most possible toward that end.

Most limestones contain some percentage of magnesium, and in the case of a pure dolomite over 45% carbonate is present in combination with calcium carbonate. A stone rich in magnesium slakes less readily than one high in calcium, and therefore is preferred by manufacturers s.h.i.+pping pulverized burnt lime to reach its destination before slaking.

CHAPTER XV

WHAT SHALL ONE BUY?

_Relative Values._ The relative strengths of the various materials containing lime may be known and yet doubt continue respecting the choice to be made. The conflicting claims of dealers, and inaccurate deductions from a single test made by some individual, aid the confusion. If there were always the single purpose of correcting soil acidity, and if there were the same ease of application in case of all the materials, the choice would present much less difficulty.

Notwithstanding this, most land now has a lime requirement, or will have one as leaching, crop removal and chemical change within the soil continue, and the puzzle is no worse than a score of others that present themselves continuously in farming.

_Destroying Acids._ The cost of liming to improve the physical condition of land is prohibitive for most farms remote from supplies of stone that can be burned and put upon the land at a low price per ton. Where stone is at hand, and soils are intractable, lime burned on the farm should be used. Some slight benefit to a stiff soil may be obtained from the light application that is deemed practicable where all forms are costly, but this benefit is not usually marked in case of an application of a ton or less of burned lime. It is a safe statement that most buyers of lime in some form or other will profit chiefly through the correction of soil acidity and promotion of bacterial life. This renders the situation more simple as any carbonate, hydrate or oxide of lime will accomplish these purposes.

_Composition._ The first consideration is the actual content of calcium and magnesium. A guaranteed a.n.a.lysis is the only safe basis of purchase.

The unstable nature of fresh burned and hydrated forms makes an exact statement of percentages impossible for goods not wholly fresh, but at least the purity of the original limestone can be judged.