that would be produced by the direct application of a similar quantity of lime. It is, however, apparent that some descriptions of marl, though advantageously employed on most soils, do not contain any, or only a very small portion of the carbonate of lime; its efficacy therefore cannot be solely attributable to that cause*, and it must possess some other property from which its influence upon the land is partly derived. This may consist either in the change which its application produces in the texture of the ground through the mere increase of its bulk, which, by its dense and unctuous quality, also adds to the consistence and value of all light soils; or, by the more perfect combination of the particles of which it is formed, by which its powers are brought into full action, and lime, sand, and clay are each made to bear against each other, and thus aid its mechanical operation on the land. All marl, except those species which are combined with large portions of iron, sulphur, or deleterious mineral substances, also of itself affords nourishment to corn and vegetables; it must, therefore, be considered as a soil, and when laid upon the land, this addition must necessarily yield a more abundant support to succeeding crops.

If this view of the subject be correct, it may be assumed, that all kinds of marl which abound in calcareous matter may be considered applicable to every soil to which lime is beneficial; subject, however, to the effect which may be also produced by the other portions of their substance when applied to land of a peculiar nature. Thus as we have already more fully stated in the preceding part of our observations-on light, sandy, and gravelly soils, an advantage is gained by the large quantity of clay which the marl appropriate to such land usually contains, by rendering them more stiff and impervious to the rain, and therefore stronger: on wet and heavy lands, on the contrary, as it renders the soil more retentive, unless very great care be bestowed on their drainage, it may occasion permanent injury; but shell and stone-marl occasions it to become loose and friable. Attention should therefore be paid, not only to the nature of the marl, but to that also of the soil to which it is to be applied; and when a choice of marl can be procured, its earthy portion should differ as widely as possible from that of the ground upon which it is intended to be laid.

In fine, marl may be considered as an improver of the soil under so many different circumstances, that it can hardly be recommended in too strong terms; for if it be used with judgment, it adds staple to the soil, improves its quality, and renders the application of putrescent manure more effectual. The use which some farmers make of it, however, deserves the highest censure, many of them taking repeated crops of oats in the interval of one summer-fallow for wheat, by way of cleansing the land; after which, barley and oats again, as long as the land will produce anything, until it is at last laid down with weeds and couch-grass.' Such is the view taken of their conduct by the surveyor of Lancashire, where it is very extensively employed, and in which opinion he is by no means singular. The rotation which he recommends-with reference, of course, to land that is not too strong-is, to take one crop of oats the spring subsequent to marling; plough the stubble immediately, in order to expose the marl again to the influence of the frost; fallow, with manure, for turnips—a crop which, under this management, is never known to fail; then barley, clover,

*Out of twelve specimens of marl [submitted to the inspection of Sir Humphry Davy, eleven were found to contain calcareous earth in various proportions; but the result of many other trials of marls, procured from different parts of the country, and found by farmers to produce an ameliorating effect upon the land, yet proves them to be, in many instances, wholly deficient in that substance. See the section on Marl, in Holland's Survey of Cheshire.

wheat, turnips fed off with sheep, and barley again, with well-dressed hayseeds, and white clover and trefoil for a perennial ley, or at least for some years*. Under which management, poor land may, when properly tilled and duly supplied with putrescent manure, be rendered highly exuberant without being in the least degree harassed.

ANALYSIS OF MARL.

The value of marl, as a manure, must of course be referable to the nature of the different kinds employed. It is, indeed, evident that, being intended to correct or improve the soil, its constituent parts should be known, and their qualities explained, before any use can be rationally made of it; and, therefore, the more accurately its properties are ascertained, the more confidently may the propriety of its application be determined. Farmers, indeed, cannot be expected to be sufficiently acquainted with chemistry to be able to analyze it, though the most calcareous sorts may be known by means of acids, as applied to lime; or, the common earthy kind, when put into water, will fall to pieces, allowing a considerable portion of sand to fall to the bottom of the vessel: by which simple tests, they might often derive considerable advantage. Its qualities are, however, more generally taken, by mere practical men, more upon trust derived from the experience of their neighbours than from any actual knowledge of its properties; but although, when thus guided, they cannot go far wrong, yet they may be misled by circumstances of slight apparent difference, and, in cases of new pits being opened, no certain estimate of its effect can be formed until a complete analysis has been made. This should, indeed, be done in all such instances; for it costs but a trifle, is easily performed, and without having recourse for the purpose to a regular scientific chemist, the object may be attained by application to any intelligent apothecary, by furnishing him with the following account of the modes of procedure :—

The ingredient of marls, on which their fitness for agricultural purposes depends, is the carbonate of lime. It is owing to the presence of this earth that marls effervesce on the addition of acids, which is one of their distinguishing characters: to ascertain which

Let the marl be put into a glass, partly filled with water, which will expel a portion of acid contained mechanically in the marl, and thus obviate one source of fallacy. When the marl is thoroughly penetrated by the water, add a little muriatic acid, or spirit of salt. If a discharge of air should ensue, the marly nature of the earth will be sufficiently established.'

Then, to find their composition

'Pour a few ounces of diluted muriatic acid into a Florence flask, place them in a scale, and let them be balanced. Then reduce a few ounces of dried marl into powder, and let this powder be carefully and gradually thrown into the flask, until, after repeated additions, no further effervescence is perceived. Let the remainder of the pow dered marl be weighed, by which the quantity projected will be known. Let the balance be then restored. The difference of weight between the quantity projected, and that requisite to restore the balance, will show the weight of the air lost during the effervescence, and will stand thus,

If the loss amount to 13 per cent. of the quantity of marl projected, or from 13 to 32 per cent., the marl assayed is calcareous marl, or rich calcareous earth.

Clayey marls, or those in which the argillaceous ingredient prevails, lose only 8 or 10 per cent. of their weight by this treatment; and sandy marls about the same proportion. The presence of much argillaceous earth may be judged by digging the mari, after being washed with spirit of salt, when it will harden, and form a brick+.

* Dickson's Lancashire, Stevenson's edit., p. 491.

Henry's Elem. of Exper. Chem., vol. ii. chap. xv. sect. iii. See also Kirwan on Manures, p. 12.

CHAPTER XIV.

MINERAL MANURES, continued.-GYPSUM.

GYPSUM,

Otherwise sulphate of lime, or plaster of Paris, as it is sometimes termed, from having been dug in great quantities from the quarries at Mont Martre, is a fossil, of which 100 parts of that kind chiefly used as manure have been described by Chaptal and Buchholtz-both eminent writers on chemistry-as consisting of

It requires from 450 to 500 times its own weight of water to dissolve it; though reducible to powder in the fire, it is almost as difficult of fusion as limestone, and it loses about 20 per cent. by calcination. When pure, it does not effervesce with acids; it is insipid in taste, and free from smell; but there are other sorts which vary in purity, and hence the analyses of many chemists differ in their accounts of its properties. There is, however, a simple mode of trying its quality, which is common in America, and consists in putting a quantity of it pulverized into a dry pot over the fire; and when heated, it gives out a sulphurous smell. If the ebullition, or bubbling, which then takes place, is considerable, the plaster is good; but if not, it is considered indifferent; and if it remains motionless, like sand, it is thought to be hardly worth anything*. Another test of its goodness is obtained by putting the powder alone into an iron pot over the fire, and when it bubbles, like boiling water, it will admit of a straw being thrust to the bottom without resistance. It is found in this and other countries, in many mountains of secondary height; sometimes in huge semi-transparent masses of great hardness, and also in a state of powdert. In England the chief mines of the stony kind at present worked are in Derbyshire, and that which is in a loose state is principally dug in Nottinghamshire; but it is also known on the coasts of Hants and Dorset, and there is a large vein of it at Ballintrae, in Ayrshire, from whence it may be carried coastwise at a moderate expense. In colour it is generally white or grey, but tinged with darker shades as it partakes of other matter; and when found in a solid form, it is composed of fibres which are sometimes thick, at others fine and subtile, adhering to each other, and very brittle.

The use of gypsum, as a manure, though only of late years brought into general notice, is not a modern discovery, for traces of it are to be found in the writings of the ancients. It was not, however, until towards the middle of the last century that the public attention was attracted to it by

* Parkinson's Practical Observations on Gypsum, p. 36.

When found in this state, it has, in some parts of the continent, and in times of famine, been regarded as a species of flour sent by heaven for the support of man; whence it has obtained the name of celestial flour, and has been made into bread when mixed with that of grain. It cannot, however, be supposed that it really contains any power of affording nourishment; but it does not possess those deleterious qualities which many people attribute to it; and it is said to be used by some bakers to add weight to their loaves.

When made up into a paste, it is also used by printers for retaining an impression of their types, by which simple process the copies of literary works are stereotyped.

Y

the account of experiments made by some distinguished agriculturists in Germany, and published by the Economical Society of Berne, through whose recommendation it was immediately introduced into Switzerland. Thence its fame gradually spread over many parts of the Continent of Europe, and at length reached Pennsylvania, where it has been so extensively used, that, after having been largely imported from France, it has been sometimes conveyed by land-carriage upwards of 150 miles from the Delaware, until it was at length discovered in the state of New York, and in other provinces of the Union. Surprising effects have been attributed to its powers of fertilization upon particular crops, both throughout Germany and in most places where it has been tried in America. It has been there stated, in one account published at Philadelphia, and widely disseminated in England by a company established in London for the sale of what they termed patent gypsum, that early Virginian wheat having been sown on exhausted land, at the rate of three bushels per acre, it yielded forty of the finest grain, which weighed 64 lbs. per bushel, and ripened before the earliest rye; that by spreading two bushels and a half of plaster on an acre, three times as much clover has been grown as when it was not sown; and in another, that six bushels have been found preferable to fifty carts-load of the best dung *. Yet many of those experiments have failed, and in a series very accurately conducted at General Washington's farm of Mount Vernon, in which the mode of its application was varied in different ways and proportions, from one to twenty bushels per acre,-every-trial proved uniformly unsuccessful. Mr. Parkinson, too, who resided a considerable time in the United States, and has written upon their farming, denies its effects, except on some particular crops; and as to the dung, in competition with which it was used, he says that the farm-yard manure in that country is of little value; for it is ill managed, the straw weak, and the generality of the horned cattle so poor that their dung is light and worthless: to which he adds, that their common farm-carts contain no more than a large wheelbarrow t.

In England its progress has been much slower, and the account given of its effects are singularly contradictory. In Scotland, and in many other parts of the United Kingdom, it has been found nearly inefficient; yet on Mr. Coke's farm at Holkham, in Norfolk, great benefit has been derived from laying it, in powder, at the rate of four bushels an acre upon sainfoin layers §, the crops of which it is said in other accounts to have in some instances doubled. In some experiments also, made in Kent, and recorded in the Communications to the Board of Agriculture, it appears to have been employed with such advantage on calcareous sandy loam, and even on stiff soils which had been previously chalked, that it is said to have increased clover and lucerne at least three fold, and to have proved equally beneficial to leguminous crops. Thus it has been stated by Mr. Smith, of Tunstal, near Sittingbourne, that having a field of red clover which had been manured with gypsum, and had produced a very fine crop,

* Dr. Fothergill, M.D., F.R.S., of Philadelphia, on Gypsum. Communications to the Board of Agriculture, vol. vi. lect. 49. See also an account by S. Powell, Esq., Pres. of the Philad. Agric. Soc., in the Annals of Agriculture, vol. x.; and various experiments on gypsum in different parts of the United States and Canada, recorded in the following volumes of the same 'work-vii. pp. 7, 186, 334, 447, 553; xv. p. 89; xx. p. 76; xxv. p. 334; xxviii. p. 641; xxx. p. 39.

Parkinson's Practical Observations on Gypsum, as a Manure, p. 16—20.

General Report of Scotland, vol. ii. p. 537, and Naismith on Manures, App. to the

Gen. Rep., vol. ii. p. 75.

§ Blaikie on Mildew, 2nd edit., p. 35.

he carefully repeated the trial on two square perches-one, carefully spread in the middle of April, with powdered gypsum, at the rate of five bushels the acre, and the other without any: the result of which experiment on the crops, when mown for hay, and afterwards cut for seed, was as follows:

The cost of the gypsum was then 5s. per bushel, though now much less, and he values the difference between the two crops at no less than 16l. 2s. 9d. in favour of the experiment: to which he adds, that he had besides 10 acres of lucerne, 5 of sainfoin, and 3 of Dutch clover, each dressed with a similar quantity of gypsum, as a top-dressing, which, to all appearance, received equal benefit.

He says cattle show such a remarkable predilection for clover which has been gypsumed, that, after having once tasted it, they have been observed to walk deliberately to it the whole length of a field without tasting a part that was grown without it, though a tolerably good crop; and in his opinion it not only increases the vigour and the verdure of the plant, but also perceptibly increases the richness of its juices *.

The following experiments upon its application-comparatively with ashes-to perches of clover, afterwards cut in full head, also show it to have been attended with superior effect:

Nos. 1 & 2. Sprinkled separately with one and two quarts of gypsum.

three and four

Do.

The produce of the last was, in Nos. 1 and 2, equal, and rather superior, to those of Nos. 3 and 4; that of No. 5 was the worst; but each patch, when compared with the adjoining land, that had no manure, was not only considerably higher, but thicker, of a deeper and more luxuriant colour, and of a broader leaf t.

In various other repeated trials made with great care and attention upon sainfoin, sown on poor light chalky land, the several results also showed a considerable balance in favour of the application of gypsum; the hay-crop yielding so abundantly as to exceed that upon which it had not been laid by an average of forty-four shillings an acre: it likewise afforded a proportionate increase of sheep-pasture, and, if sown with peas, when looking up, it generally produced immense crops. It has also been laid down, at the rate of five bushels, with similar success, upon clover, on a certain portion of the land, in the middle of a large field, where the soil was of the same quality; the entire field was then sown in the following November with wheat, the appearance of which, in both colour and strength, on that part which was gypsumed, became very apparent in the month of May, and was

Communications to the Board of Agriculture, vol. iii. p. 337.

† Annals of Agric., vol. xvi. pp. 303 and 184. A quart to the perch is equal to five bushels to the acre.