powerful manuring substances (ammonia, nitric, phosphoric acid and potash), the weaker of course must be the product derived from them.

The employment of quick-lime must also claim a few words here, since this is very useful at the right time, but may do much injury at an improper time. The general rule to be followed here is, that we may add lime to the compost only at first, but never late or after it has fermented more or less. In fermentation and putrefaction, the most valuable constituents of animal and vegetable substances give origin to salts of ammonia, which would be so decomposed by adding lime, that the ammonia would be set free, rendered volatile, and would pass off into the air. Unfermented organic matters, on the contrary, may be moderately sprinkled with lime without apprehension, to create a more rapid rotting and decomposition; only in that case, particularly with animal substances, which contain much nitrogen and therefore yield much ammonia, care must be taken that they are covered several inches deep with a layer of porous, substances, such as peat, rubbish, humous earth, saw-dust with soot, &c., which will swallow up the volatile products of putrefaction. With substances difficult of decomposition, such as hoofs, horn, leather, hair, wool, &c., the reduction of which is essentially promoted by quick-lime and wood-ashes, it might be advantageous to establish separate compostheaps, since the complete decomposition of these will mostly require a longer time than that of other materials.

If a perceptibly pungent smell is emitted from the heaps, or even only when they are forked over, they may be covered over afresh with a layer of moist humous earth, or refuse of peat; or watered with dilute sulphuric acid or other acid liquid, provided these can be obtained; or sprinkled with a solution of sulphate of iron (green vitriol), these combining with and retaining the volatile ammonia. Addition of gypsum and gypsiferous materials, such as peat-ashes, acts in a similar manner, but only when mixed with a sufficient abundance of water, so that they form at least a thin cream. We have an accurate and simple means of detecting the escape of ammonia, in a feather dipped in hydrochloric (muriatic) acid. When this is held over the spot to be tested, a thick white cloud is formed round the feather if ammonia is escaping.

Another test is reddened litmus paper, which becomes blue in air containing ammonia.

4. In reference to mechanical manipulations in the preparation of compost-heaps, the farmer will have a better guide in his practical sense and experience than I could give him, I therefore confine myself here to a few indications. In the first place I remind him, that the same requisites which are demanded in making a good dung-heap, are applicable to the compost-heaps, therefore that, in laying the foundation, care must be taken that none of the liquids of the heap can drain away into the earth which forms the bed, and that no water shall be able to penetrate from without, except what falls directly upon it in rain. It is equally self-evident that earth, ash, mud, &c. should be sifted previously, so as not to add stones, slags, &c. to the mass, as unnecessary ballast; that the materials generally should be carefully broken small and mixed together or laid on in regular layers, so as to obtain a uniform mixture and a uniform fermentation and heating. The suitable height for a compost-heap may be stated at about 4 feet. The circumference should be at least sufficient to prevent the heap freezing in winter; a covering of brush-wood or leaves, to keep off the cold in winter, appears quite advisable. Perhaps it would be good to make large heaps at first, and afterwards, when the assistance of atmospheric air becomes desirable, to divide them into smaller, at the first or second turning-over. What is called "the period of ripening" will then be denoted by the mass having become so rotten that it may be easily crumbled. It will depend essentially on the composition of the mass and its treatment whether this epoch is attained in half a year or in two years. I do not doubt that it would be possible to shorten the now ordinary time considerably, without loss or injury, if endeavours were made to fulfil as completely as possible the described conditions of graduated succession of fermentation, putrefaction and decay. I cannot give any simple process for ascertaining the manuring value of the fully ripe compost; the great qualitative and quantitative difference of the materials used in the preparation, render a chemical analysis necessary to give an account of the quantity of the manuring substances actually contained. However, the farmer may always make an approximative

estimate as to the manuring power of his compost, from the ingredients used in preparing and wetting it, if he has only taken pretty correct note of their kind and quantity.

Any instructive communications or practical observations and experience in the department of compost-making will be very welcome to me.

XVI. SOILS, SURFACE SOIL OR MOULD.

Ir a plant is to grow up strongly and freely, it must have not only good and abundant food, but a suitable and healthy abode; it must be well-fed and well-bedded. In the foregoing sections we have discussed what science can at present offer to practice on the subject of feeding or manuring plants; in the following I shall endeavour to collect together the practically important points in what science has hitherto been able to make out regarding the peculiar dwelling-place of plants, regarding soil, its variations, and its relation to the growth of vegetation.

I must here premise a general observation, in order to indicate at the outset what may be expected and demanded from the study and investigation of soils, according to their present state of development. It is frequent, nay most usual to expect and require from them, far more than they are able to accomplish, and chemists themselves have not rarely promised to accomplish more through them than could possibly be performed, and thus have contributed to this over-valuation. Not long ago it was expected of me, that by the help of chemical analysis, I should be able to give legal evidence whether or not the fields of an estate were in well-manured condition. I took the pains, at the time, simply to calculate the dilution the manures would suffer in the soil, and among other things it came to light, that the most important food of plants, the nitrogen, laid on a soil in a strong manuring with dung, amounted, on a field with a soil averaging only 5 or 6 inches deep, to at most

15,000

dth of the weight of the soil, and in a strong manuring with guano to at most dth. To this it must be added,

1 40,000

that the natural insoluble nitrogen contained in the soil of poor fields, even when these are exhausted, is often 5 to 10 times, and in rich fields 50 to 100 times greater than the amount of nitrogen given to the soil in an abundant manuring with guano. It is self-evident that chemical investigation could have no judicial exactness under such circumstances. To determine the productive power of a soil, or to value it by a chemical analysis of its ingredients, is not at present possible, and will remain impossible, since the fertility of a soil by no means depends on its chemical composition alone. But this will certainly be able to furnish useful hints to the valuer, and useful advice to the practising farmer, when the methods of investigation cease to inquire, one-sidedly, only the amounts and nature of the constituents, and become directed to their condition and solubility, and at the same time to their physical characteristics. Most of the innumerable analyses of soils at present known are onesided or unpractical and untrustworthy, hence they have not benefited practice at all, or comparatively very little.

And what is termed now the study of soils, is not an independent science, far rather is it a more or less arbitrary conglomeration of chemical, physical, geological, mineralogical, meteorological and agricultural maxims and isolated facts. From its nature, moreover, the study of soils does not form a special science, but a definite, necessary component of agricultural chemistry; and therefore it must be intercalated in this, and in the extension and progress of this must be extended and advanced with it more uniformly and exactly than has hitherto happened. Practice appears here more certain and definite than science, and the latter has work to do merely to come slowly after. The only trustworthy path which she has struck out, is here also that of letting the laboratory and the field mutually control each other.

From what I have just been able hastily to indicate, the reader must be prepared in this part of agricultural chemistry, to receive more theoretical explanations and conjectures, than certain proofs and useful practical applications. Yet I venture to hope that these will not be considered unworthy of his attention, although they may not prove of

earth from one spot and deposit them as mud in another. A further indication of the magnitude of the floods to which the surface of our earth has been exposed, is afforded by the fact that we meet with soils of this kind, called alluvial soils or alluvial land, not merely in low-lying districts, but often at a considerable elevation above them*. Thus recent researches have demonstrated in Saxony, that the great flood which diffused the boulders called "foundlings" (probably granite and other rocks conveyed hither from Sweden and Norway) over the whole North German plain, must have reached a height of about 1000 feet in Saxony, and that all the soil of this country, from the plain to this elevation, is to be regarded as alluvial soil.

Causes of Weathering and Decay.

The forces effecting the breaking down of rock into earth, still continue to act constantly in this, and impart to it the capability of becoming and remaining a supporter and sustainer of vegetable growth. The principal of these are the following:

Through the alternations of heat and cold, cracks and fissures are formed in the most solid rocks; with the assistance of air and water the cracks are deepened and widened, and separate fragments are detached from their connexion with the great whole. Through the same alternations of temperature a daily circulation of air is produced in the porous soil, conveying new supplies of air to this at every new cooling down. Moreover all chemical processes go on more rapidly and energetically at a high than at a low temperature; therefore the warmer a country, or spot, or a soil is, the more actively will weathering and decomposition proceed in it.

Air, in union with the watery vapour always present in it, affords oxygen or water to all bodies which have a tendency to combine with these substances. The particles of iron (protoxide of iron), which scarcely any rock is without, make use of it, and become converted into iron rust, which does not possess a fixing or binding power like protoxide of

The author omits to notice the more natural way of accounting for this, viz. upheaval of the land subsequently to the formation of the de posits.-A.H.