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tility, as ten times that proportion, under other

circumstances.

ion had not been contradicted by later and better authority: and the only support that I can look for, will be in the facts and arguments that I shall be able to adduce.

In all naturally poor soils, producing freely, in their virgin state, pine and whortleberry, and sorrel after cultivation, I suppose to have been formed some vegetable acid, which, after taking up whatever small quantity of lime might have been present, still remains in excess in the soil, and nourishes in the highest degree the plants named above, but is a poison to all useful crops; and effectually prevents such soils becoming rich, from either na-ed with propriety to soils, in which growing vegetural or artificial applications of putrescent ma

nures.

In a neutral soil, I suppose calcareous earth to have been sufficiently abundant to produce a high degree of fertility-but that it has been decomposed, and the lime taken up, by the gradual formation of vegetable acid, until the lime and the acid neutralize and balance each other, leaving no considerable excess of either. Such are all our fertile soils that are not calcareous.

These suppositions remain to be proved, in their parts.

all

I am not prepared to question what Grisenthwaite states as a chemical fact, "that no soil was ever yet found to contain any notable quantity of acid." No soil examined by me for this purpose, gave any evidence of the presence of uncombined acid. Still, however, the term acid may be applitables continually receive acid from the decomposition of others, (for which no "fixity is requisite,) or in which acid is present, not free, but combined with some base, by which it is readily yielded to promote, or retard, the growth of plants in contact with it. It will be sufficient for my purpose to show that certain soils contain some substance, or possess some quality, which promotes almost exclusively the growth of acid plants-that this power is strengthened by adding known vegetable acids to the soil-and is totally removed by the application of calcareous manures, which would necessarily destroy any acid, if it were present. Leaving it to chemists to determine the nature and properties of this substance, I merely contend for its existence and effects: and the cause of these effects, whatever it may be, for the want of a better name, I shall call acidity.

The proofs now to be offered in support of the existence of acid and neutral soils, however weak each may be when considered alone, yet when taken in connexion, will together form a body of evidence not easily to be resisted.

No opinion has been yet advanced that is less supported by good authority, or to which more general opposition may be expected, than that which supposes the existence of acid soils. The term sour soil is frequently used by farmers, but in so loose a manner as to deserve no consideration: it has been thus applied to any cold and ungrateful land, without intending that the term should be literally understood, and perhaps without attaching to its use any precise meaning whatever. Dundonald only, of all those who have applied chemistry to agriculture, has asserted the exist- 1st Proof. Pine and common sorrel have leaves ence of vegetable acid in soils:* but he has offer- well known to be acid to the taste; and their ed no analysis, nor any other evidence to establish growth is favored by the soils which I suppose to the fact and his opinion has received no confirm- be acid, to an extent which would be thought reation, nor even the slightest notice, from later and markable in other plants on the richest soils. Exmore able investigators of the chemical characters cept wild locust on the best river land, no growth of soils. Kirwan and Davy profess to enumerate can compare in rapidity with pines on soils natuall the common ingredients of soils, and it is not rally poor, and even greatly reduced by long cultiintimated by either, that vegetable acid is one of vation. Pines usually stand so thick on old exthem. Even this tacit denial by Davy, more hausted fields, that the increase of size in each strongly opposes the existence of vegetable acid, plant is greatly retarded-but if the whole growth than it is supported by the opinion of Dundonald, of an acre is estimated, it would probably exceed or any of those writers on agriculture who have in quantity the different growth of the richest admitted its existence. Grisenthwaite, a late wri- soils, of the same age and on an equal space. ter on agricultural chemistry, and who has the ad- Every cultivator of corn on poor light soil knows vantage of knowing the discoveries, and compar-how rapidly sorrel will cover his otherwise naked ing the opinions of all his predecessors, expressly denies the possibility of any acid existing in soils. His New Theory of Agriculture contains the following passage: "Chalk has been recommended "as a substance calculated to correct the sourness "of land. It would surely have been a wise "practice to have previously ascertained this ex"istence of acid, and to have determined its nature, "in order that it might be effectually removed. "The fact really is, that no soil was ever yet found "to contain any notable quantity of acid. The "acetic and the carbonic are the only two that are "likely to be generated by any spontaneous de"composition of animal or vegetable bodies, and "neither of them have any fixity when exposed "to the air." Thus, then, my doctrine is deprived of even the feeble support it might have had from Dundonald's mere opinion, it that opin

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field, unless kept in check by continual tillageand that to root it out, so as to prevent the like future labor, cannot be effected by any mode of cultivation whatever. This weed too is considered far more hurtful to growing crops, than any other of equal size. Yet neither of these acid plants can thrive on the best lands. Sorrel cannot even live on a calcareous soil-and if a pine is sometimes found there, it has nothing of its usual elegant form, but seems as stunted and ill shaped as if it had always suffered for want of nourishment. Innumerable facts, of which these are examples, prove that these acid plants must derive from their

* Sheep sorrel, or Rumex acetosa. The wood sorrel This prefers rich and calcareous soils, and I have seen (oxalis acetocella) is of a very different character. it growing on places calcareous to excess. It would seem, therefore, that wood sorrel forms its acid from the atmosphere, and does not draw it from the soil, as is evidently the case with common sorrel.

24

favorite soil some kind of food peculiarly suited to their growth, and quite useless, if not hurtful, to cultivated crops.

weeks of growing weather will bring out that plant close around every heap-and for some time, it will continue to show more benefit from that rank manuring than any other grass. For several years my winter-made manure was spread and ploughed in on land not cultivated until the next autumn, or the spring after. This practice was founded on the mistaken opinion, that it would prevent much of the usual exposure to evaporation and waste of the manure.

One of the reasons which alone would have compelled me to abandon this absurd practice, was, that a crop of sorrel always followed, (even on good soils that before barely permitted a scanty growth to live,) which so injured the next grain crop as greatly to lessen the benefit from the manure. Sorrel unnaturally produced by such applications, does not infest the land longer than until we may suppose the acid to have been removed by cultivation, and other causes.

2. Dead acid plants are the most effectual in promoting the growth of living ones. When pine leaves are applied to a soil, whatever acid they contain is of course given to that soil, for such time as circumstances permit it to retain its form, or peculiar properties. Such an application is often made on a large scale, by cutting down the second growth of pines, on land once under tillage, and suffering them to lie a year before clearing and cultivating the land. The invariable consequence of this course, is a growth of sorrel for one or two crops, so abundant and so injurious to the crops, as to more than balance any benefit derived by the soil, from the vegetable matter having been allowed to rot. From the general experience of this effect, most persons put pine land under tillage as soon as cut down, after carefully burning the whole It may be objected that my authorities prove of the heavy cover of leaves, both green and dry. only the formation of a single vegetable acid in Until within a few years, it was generally sup- soil, the acetic-that my facts show only the proposed that the leaves of pine were worthless, if duction of a single acid plant, sorrel-and that the not hurtful, in all applications to cultivated land-acid which sorrel contains is not the acetic, but the which opinion doubtless was founded on such facts as have been just stated. But if they are used as litter for cattle, and heaped to ferment, the injurious quality of pine leaves is destroyed, and they become a valuable manure. This practice is but of recent origin-but is highly approved, and rapidly extending.

On one of the washed and barren declivities (or galls) which are so numerous on all our farms, I had the small gullies packed full of green pine bushes, and then covered with the earth drawn from the equally barren intervening ridges, so as nearly to smooth the whole surface. The whole piece had borne nothing previously except a few scattered tufts of poverty grass, and dwarfish sorrel, all of which did not prevent the spot seeming quite bare at midsummer, if viewed at the distance of one hundred yards. This operation was performed in February or March. The land was not cultivated, nor again observed until the second summer afterwards. At that time, the piece remained as bare as formerly, except along the filled gullies, which throughout the whole of their crooked courses, were covered by a thick and tall growth of sorrel, remarkably luxuriant for any situation, and which being bounded exactly by the width of the narrow gullies, had the appearance of some vegetable sown thickly in drills, and kept clean by tillage. So great an effect of this kind has not been produced within my knowledge-though facts of like nature and leading to the same conclusion, are of frequent occurrence. If small pines standing thinly over a broom-grass old field, are cut down and left to lie, under every top will be found a patch of sorrel, before the leaves have all rotted.

oxalic.* From the application of acids to recently ploughed land, no acid plant except sorrel is made to grow, because that only can spring up speedily enough to arrest the fleeting nutriment. Poverty grass grows only on the same kinds of soil, and generally covers them after they have been a year free from a crop, but does not show sooner-and pines require two years before their seeds will produce plants. But when pines begin to spread over the land, they soon put an end to the growth of all other plants, and are abundantly supplied with their acid food, from the dropping of their own leaves. Thus they may be first suppiied with the vegetable acid ready formed in the leaves, and afterwards with the acetic acid, formed by their subsequent slow decomposition. It does not weaken my argument, that the product of a plant is a vegetable acid different from the one sup-. posed to have nourished its growth. All vegetable acids (except the prussic) however different in their properties, are conposed of the same three elementary bodies, differing only in their proportionst-and consequently are all convertible into each other. A little more, or a little less of one or the other of these ingredients, may change the acetic to the oxalic acid, and that to any other. We cannot doubt but that such simple changes may be produced by the chemical powers of vegetation, when others are effected, far more difficult for us to comprehend. The most tender and feeble organs, and the mildest juices, aided by the power of animal or vegetable life, are able to produce decompositions and combinations, which the chemist cannot explain, and which he would in vain attempt to imitate.

4. This ingredient of soils which nourishes acid 3. The growth of sorrel is not only peculiarly plants, also poisons cultivated crops. Plants have favored by the application of vegetables contain- not the power of rejecting noxious fluids, but take ing acids already formed, but also by such matters up by their roots every thing presented in a soluble as will form acid in the course of their decomposi- form. Thus the acid also enters the sap-vessels tion. Farm-yard manure, and all other putres- of cultivated plants, stunts their growth, and makes cent animal and vegetable substances, form acetic acid as their decomposition proceeds.* If heaps of rotting manure are left without being spread, in a field the least subject to produce sorrel, a few

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* Agr. Chem. Lecture 3.

† Carbon, Oxygen and Hydrogen. Agr. Chem. Lecture 3, p. 78.

Agr. Chem. Lecture 6, page 186.

gas, and therefore could have contained no carbonate of lime. The precipitate obtained from the same weighed sixteen grains-which being again acted on by sulphuric acid, evolved as much gas as showed that three grains had become carbonate of lime, in the previous part of the process.

impossible for them to attain that size and perfection, which their proper food would ensure, if it was presented to them without its poisonous accompaniment. When the poorest virgin woodland is cut down, it is covered and filled to excess with leaves and other rotted and rotting vegetable matters. Can a heavier vegetable manuring be Two hundred grains of alluvial soil from Saradesired? And as it completely rots during cultiva- toga Springs (page 21, No. 18,) containing no cartion, must not it offer to the growing plants as bonate of lime, yielded a precipitate of twelve abundant a supply of food as they can require?-grains, of which three was carbonate of lime-and Yet the best product obtained may be from ten to a deposite from the alkaline solution weighing six fifteen bushels of corn, or five or six of wheat, grains, four of which was carbonate of lime. soon to come down to half those quantities. If the Seven hundred grains of limestone soil from noxious quality which causes such injury is an Bedford (part of the specimen marked 14, page acid, it is as certain as any chemical truth what- 21,) contained about two-thirds of a grain of carever, that it will be neutralized, and its powers de-bonate of lime-and its precipitate of twenty-eight stroyed, by applying enough of calcareous earth grains, only yielded two grains: but the alkaline to the soil: and precisely such effects are found solution deposited eleven grains of the carbonates whenever that remedy is tried. On land thus re- of lime and magnesia, of which at least five was lieved of this unceasing annoyance, the young of the former, as there remained seven and a half corn no longer appears of a pale and sickly green, of solid matter, after the action of sulphuric acid.* approaching to yellow, but takes immediately a deep healthy color, by which it may readily be distinguished from any on soil left in its former state, before there is any perceptible difference in the size of the plants. The crop will produce fifty to one hundred per cent. more, the first year, before its supply of food can possibly have been increased and the soil is soon found not only cleared of sorrel, but incapable of producing it. I have anticipated these effects of calcareous manures, before furnishing the proof-but they will hereafter be established beyond contradiction.

The truth of the existence of either acid, or neutral soils, depends on the existence of the other -and to prove either, will necessarily establish both. If acid exists in soils, then wherever it meets with calcareous earth, the two substances must combine and neutralize each other, so far as their proportions are properly adjusted. On the other hand, if I can show that compounds of lime and vegetable acid are present in most soils, it follows inevitably that nature has provided means by which soils can generally obtain this acid: and if the amount formed can balance the lime, the operation of the same causes can exceed that quantity, and leave an excess of free acid. From these premises will be deduced the following proofs.

5. It has been stated (page 18) that the process recommended by chemists for finding the calcareous earth in soils was unfit for that purpose, because a precipitate was always obtained even when no calcareous earth, or carbonate of lime was present. Frequent trials have shown me that this precipitate is considerably more abundant from good soils than bad. The substance thus obtained from rich soils by solution and precipitation, in every case that I have tried, contains some calcareous earth, although the soil from which it was derived had none. The alkaline liquor from which the precipitate has been separated, we are told by Davy will, after boiling, let fall the carbonate of magnesia, if any had been in the soil: but when any notable deposite is thus obtained, it will often be found to consist more of carbonate of lime, than of magnesia. The following are examples of such products:

From this process, there can be no doubt but that the soil contained a proportion of some salt of lime (or lime combined with some kind of acid) which being decomposed by and combined with the muriatic acid, was then precipitated, not in its first form, but in that of enrbonate of lime--it being supplied with carbonic acid from the carbonate of potash, used to produce the precipitation. The proportions obtained in these cases were small; but it does not follow that the whole quantity of lime contained in the soil was found. However, to the extent of this small proportion of lime is proved clearly the presence of enough of some acid (and that not the carbonic) to combine with it. Neither could it have been the sulphuric, or the phosphoric acid: for though both the sulphate and phosphate of lime are in some soils, yet neither of these salts can be decomposed by muriatic acid.

6. The strongest objection to the doctrine of neutral soils is, that if true, the salt formed by the combination of the lime and acid must often be present in such large proportions, that it is scarcely credible that its presence and nature should not have been discovered by any of the chemists who have analyzed soils. This difficulty I cannot remove: but it may be met (or neutralized-to borrow a figure from my subject,) by showing that an equal difficulty awaits those who may support the other side of the argument.

The measurement of the carbonic acid gas evolved, was relied on to show the whole amount of carbonates present-and sulphuric acid was used to distinguish between lime and magnesia, in the deposite from the alkaline solution. If any alumine or magnesia had made part of the solid matter exposed to diluted sulphuric acid, the combinations formed would have been soluble salts, which would of course have remained dissolved and invisible in the fluid. Lime only of the four earths forms with sulphuric acid a substance but slightly soluble, and which therefore can be mostly separated in a solid form. The whole of this substance (sulphate of lime) cannot be obtained in this manner, as a part is always dissolved: but whatever is obtained, bonate of lime had been present: as that quantity of proves that at least two-thirds of that quantity of carlime which will combine with enough carbonic acid to make 100 parts (by weight) of carbonate of Time, One thousand grains of tide marsh soil (de- will combine with so much more of sulphuric acid, as scribed page 20) acted on by muriatic acid in the to form about 150 parts of the sulphate of lime, orgy ppneumatic apparatus, gave out no carbonic acid sum.

No. 1.-1000 grains yielded 7

of coarse calcareous earth, (fragments of shells.)

And less than

of finely divided.

8

The theory of geologists of the formation of Three careful examinations gave the following resoils from the decomposition, or disintegration of sults. rocks, is received as true by scientific agriculturists. The soils thus supposed to be formed, receive admixtures from each other, by means of different operations of nature, and after being more or less enriched by the decay of their own vegetable products, make the endless variety of existing soils.* But where a soil lying on, and thus supposed to have been formed from any particular kind of rock, No. 2.-1000 grains yielded 5 of coarse,

is so situated that it could not have been moved, or received considerable accessions from torrents, or other causes, then, according to this theory, the rock and the soil should be composed of the

2 finely divided.

7

2

17

same materials--and such soils as the specimens No. 3.-1500 grains yielded 15
marked 11 and 16 (page 21) would be, like the
rock they touched, nearly pure calcareous earth,
instead of being (as they were in truth) destitute,
or nearly so, of that ingredient. Such are the
doctrines received and taught by Davy, or the
unavoidable deductions from them. But without

of coarse, finely divided.

The specimens No. 1 and No. 2 were obtained by taking handfuls of soil from several places, (four well together, and then taking the samples for trial in one case, and twelve in the other) mixing them from the two parcels. On such land, when not recently ploughed, there will always be an over the rains have settled the fine soil, and left exposed proportion of the pieces of shells on the surface, as the coarse matters. On this account, in making these two selections, the upper half inch was first thrown aside, and the handful dug from below. No. 3 was taken from a spot showing a full averI considered the three trials made as fairly as posage thickness of shells, and included the surface.

contending for the full extent of this theory of the formation of soils, (because I consider it almost entirely false,) every one must admit that soils thus situated, must have received in the lapse of ages, some accessions to their bulk, from the effects of frost, rain, sun, and air, on the limestone in contact with them. All limestone soils, properly so called, exhibit certain marked and peculiar characters of color, texture, and products, which can only be derived from receiving into their composition more or less of the rock which lies beneath, or rises above their surface. This mixture will not be denied by any one who has observed limestone soils, and reasons fairly, whe-sible, to give a general average. Small as is the ther his investigation begins with the causes, or their effects. If then all this gain of calcareous earth remains in the soil, why is none, or almost none, discovered by accurate chemical analysis? Or, if it be supposed not present, nor yet changed in its chemical character, in what possible manner could a ponderous and insoluble earth have made its escape from the soil? To remove this obstacle without admitting the operation of acid in making such soils neutral, will be attended with at least as much difficulty, as any arising from that admission being made.

7. But we are not left entirely to conjecture that soils were once more calcareous than they now are, if chemical tests can be relied on to furnish proof. Acid soils that have received large quantities of calcareous earth as manure, after some time, will yield very little when analyzed. To a soil of this kind, full of vegetable matter, I applied, in 1818 and 1831, fossil shells at such a known and heavy rate as would have given to the soil (by calculation) at least three per cent. of calcareous earth, for the depth of five inches. Only a small portion of the shelly matter was very finely divided when applied. Since the application of the greater part of this dressing, (only one-fourth having been laid on in 1818,) no more than six years had passed before the following examinations were made-and the cultivation of five crops in that time, three of which were horse-hoed, must have well mixed the calcareous earth with the soil.

Agr. Chem. p. 131. Also Treatise on Agriculture (by General Armstrong) in vol. I. of American Farmer, quoted in Appendix D.

proportion of finely divided calcareous earth ex-
hibited, it must have been increased by rubbing
operation of separating them by a fine sieve. In-
some particles from the coarse fragments, in the
deed it may be doubted whether any proportion
remained very finely divided-or in other words,
whether it was not combined with acid, as fast as
it was so reduced. But without the benefit of this
supposition, the finely divided calcareous earth in
the three specimens, averaged only one and one-
fourth grains to the thousand, which is one twen-
ty-fourth of the quantity laid on: and the total
grains in one thousand, or about one-fourth of the
quantity obtained, of coarse and fine, is eight
its form, or otherwise disappeared, in the few years
All the balance had changed
original proportion.
that had passed since the application.

The very small proportions of finely divided calcareous earth compared to the coarse, in some shelly soils, furnish still stronger evidence of this kind. Of the York River soil, (described page 19, No. 5,)

1260 grains, yielded of coarse calca

1044

reous parts,
And of finely divided,

of the rich Nansemond soil,
(No. 6,)

168 grains, 8

544 coarse. 18 fine.

As many of the shells and their fragments in these soils are in a mouldering state, it is incredible that the whole quantity of finely divided particles derived from them should have amounted to no more than these small proportions. Independent of the action of natural causes, the plough

alone, in a few years, must have pulverized at-of which a remarkable example is presented in least as much of the shells, as was found. the soil of the cultivated part of the Sweet Spring Valley, (No. 8, page 21.)*

8. In other cases, where the operations of nature have been applying calcareous earth, for ages, none now remains in the soil; and the proof thence derived is more striking, than any obtained from artificial applications, of only a few years standing. Valleys subject to be frequently overflown and saturated by the water of limestone streams, must necessarily retain a new supply of calcareous earth from every such soaking and drying.

Limestone water contains the super-carbonate of lime, which is soluble: but this loses its excess of carbonic acid when left dry by evaporation, and becomes the carbonate of lime, which not being soluble, is in no danger of being removed by subsequent floods. Thus accessions are slowly but continually made, through many centuries. Yet such soils are found containing no calcareous earth

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9. All wood ashes contain salts of lime, (and most kinds in large proportions,) which could have been derived from no other source than the soil on which the trees grew. The lime thus obtained is principally combined with carbonic acid, and partly with the phosphoric, forming phosphate of lime. The table of Saussure's analyses of the ashes of numerous plants,† is sufficient to show that these products are general, if not universal. The following examples of some of my own examinations, prove that ashes yield calcareous earth in proportions suitable to their kind, although the wood grew on soils destitute of that ingredientas was ascertained with regard to each of these soils.

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The potash was first carefully taken out of all I have chosen to leave all the preceding part of these samples. The remaining solid matter was this chapter (with the exception of a few merely silicious sand, and charcoal: the proportion of the verbal corrections and alterations) precisely as it latter varying according to the degree of heat used appeared in the first edition of this essay, (January in burning the wood, which was not permitted to 1832.) But since that time I have first heard of be very strong, for fear of converting the calca- a discovery, and of consequent investigations by reous earth into quick-lime. men of science, which seem to furnish direct All the carbonate of lime yielded by ashes, was proof of what I have been contending for, viz: necessarily furnished in some form by the soil on the existence of a vegetable acid substance in soils which the plants grew-and when the soil itself and manures, generally diffused, and often in large contained no carbonate, some other compound of proportions, and yet which had not been known or lime must have been present, to enable us to ac- suspected by chemists previously. The first inticount for these certain and invariable results. The mation of this discovery which reached me was presence of a combination of lime with some ve- in the Alphabet of Scientific Gardening, by Progetable acid, and none other, would serve to pro-fessor Rennie, published in London in 1833, from duce such effects. According to established chem- which the part relative to this subject will be ical laws, if any such combination had been taken quoted below. Since then I have been enabled to up into the sap-vessels of the tree, it would be de- consult the late French work of Berzelius, in which composed by the heat necessary to convert the his views of humic acid are given more at length, wood to ashes; the acid would be reduced to its and from which an extract will be translated and elementary principles, and the lime would imme-given in the appendix. [See F.] The facts resdiately unite with the carbonic acid, (which is pecting humic acid,as concisely stated in the followproduced abundantly by the process of combustion,) and thus present a product of carbonate of lime newly formed from the materials of the other substances decomposed.‡

*The excess of carbonic acid which unites with lime and renders the compound soluble in water, is lost by On the foregoing facts and deductions, I am by evaporation to dryness. exposure of the calcareous water to the air, as well as [Accum's Chemistrycontent to rest the truth of the existence of acid Lime.] The masses of soft calcareous rock which and neutral soils. are deposited in the rapids of limestone streams, are examples of the loss of carbonic acid from exposure to the air; and the stalactites in caves, the deposite of The reasoning on the presence of the carbonate of the slow-dropping water holding in solution the super lime found in ashes from acid soils, does not apply to carbonate of lime, are examples of the same effect A similar deposite of inthe phosphate of lime which is always also present. The produced by evaporation. latter salt is not decomposed by any known degree of soluble carbonate of lime, from both these causes, is heat, [Art. Chemistry, in Edin. Ency.] and therefore necessarily made on all land subject to be overflowed might have remained unchanged, in passing from the by limestone waters. soil to the tree, and thence to the ashes. † Quoted in Agr. Chem. Lecture 3.

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