A porous substance has the power of raising water to a very remarkable extent, as may be proved by the following simple experiment.

Select a lump of common salt, cut it with a saw into a regular shape, about six inches long, two inches broad, and one inch thick, then set it to dry perfectly before a fire. Fill a shallow plate with water, containing sufficient red ink to impart a deep tint, and when the lump of salt is dry, place it upright in the plate, as here shown.

Fig. 6.

The salt, though apparently solid, is in fact full of capillary pores; these will instantly attract the reddened water, and the salt will become powerfully stained to a very considerable height. The red ink is only added to render the result more striking than it would be if water alone were employed.

In the course of a few seconds the salt will fall, on account of the chemical solvent power of the water undermining its lower part, or, in other words, on account of the solid particles of the salt being now received by the interstices between the individual atoms of the water, which action is regarded as solution; but it does not necessarily follow that a substance capable of exerting capillary attraction should thus be soluble. A lump of porous sandstone, for example, similarly placed, will at

tract water, but will not fall, even when perfectly saturated, because it is an insoluble substance.

In nature, it frequently happens that capillary attraction and chemical solution act simultaneously, and produce highly important results in conveying liquid manure to the roots of plants, by which their growth is wonderfully promoted. Vegetation on the margin of a brook, or pond, is generally more luxuriant than on the soil a few yards distant, because the porous earth of the bank attracts water abundantly, and retains it very forcibly even in time of drought.

Whilst upon this subject, it may be stated, that much of the dampness in the walls of buildings depends upon the porous brick or stone-work of the foundations attracting water from the earth, and it frequently causes great damage and inconvenience.

Oolite, or Bath-stone, as it is popularly called, is much employed in the decorative architecture of interiors, on account of the extreme facility with which it may be sawn and wrought into the most delicate tracery, and in such situations, if protected from damp, it will remain unimpaired for ages, as exemplified in many abbeys and cathedrals.

Requiring little labor from the masons, and producing a most beautiful effect, architects have been occasionally tempted to employ oolite for external work; but it is not durable, because water is rapidly absorbed by capillary attraction, and this extraordinary liquid, by undergoing expansions and contractions during the changes of atmospheric temperature, and more particularly expansion upon freezing, flakes of the stones are violently detached, and the original sharp outline of the work broken down. This action silently, though cer

tainly, continued for years, the sculptured work becomes undistinguishable.

Turning from the works of Art to those of Nature, as more particularly connected with this inquiry regarding the principal chemical phenomena of the Four Seasons, we discover capillary attraction to be a most active agent in retaining and administering a proper supply of water to the vegetation upon certain soils and rocks.

In sandstone and limestone districts, which particularly abound in England, the absorption and retention of water for the support of vegetation are very remarkable; we may see luxuriant plants, nay, even forest trees, flourishing upon both rocks, the sandstone being porous, the limestone full of cracks or fissures, all readily imbibing water from the heavens, retaining or yielding it in proportion as it is demanded, for the sustenance of vegetable life.

It is no uncommon thing in such districts to see plants and trees sending forth their roots into such cracks and fissures in search of moisture, and occasionally, when these cannot yield sufficient, the root will travel completely down the external surface of the rocks to draw a supply from the more humid soil at their base.

Different is the case when compact, glassy granite is the prevailing rock of the country; it is incapable of exerting capillary attraction for water; it cannot provide itself with vegetable clothing, and therefore stands forth in bare and gaunt outline.

When the careful agriculturist observes a particular district, in which vegetation naturally thrives, it becomes. a matter of importance with him to ascertain the cause of such fertility; and upon application to the chemist, the desired information can be obtained.

He can determine the average quantity of water absorbed and retained by the soil under ordinary vicissitudes of the atmosphere; he can determine the nature of its components, the exact proportions of sand, clay, calcareous compounds, organic, and other matters, that it contains, and can frequently artificially compose a soil equally fertile with that naturally found, or he can render it still more productive by the judicious and well-timed application of various organic and inorganic matters as

manures.

Chemistry thus becomes directly applicable to agriculture, and many agriculturists have embraced its study, and by obtaining a sound knowledge of its rudiments, have been enabled to ameliorate the condition of soils upon rational principles.

"Plants, being possessed of no locomotive powers, can grow only in places where they are supplied with food; and the soil is necessary to their existence, both in affording them nourishment, and enabling them to fix themselves in such a manner as to obey those mechanical laws by which their radicles are kept below the surface, and their leaves exposed to the free atmosphere."

"As the systems of roots, branches, and leaves are very different in different vegetables, so they flourish in most different soils; the plants that have bulbous roots require a looser and a lighter soil than such as have fibrous roots; and the plants possessing only short fibrous radicles, demand a firmer soil than such as have taproots, or extensive lateral roots."

The manner in which the chemist proceeds to analyze soils, cannot be particularly described in this examination of the Chemical Phenomena of the Four Seasons, because it involves several agents whose action would not

be readily understood; it mainly depends upon presenting to the soil some element or compound that will attract away one of its components in preference to another. This may be tangibly illustrated, in the first place, as follows.

Mix a heap of iron filings with an equal heap of sand; -let these represent two distinct components of a soil, and suppose that their ready separation is required.

If a strong magnet be thrust into the mixture, it will only attract the iron filings, and effectually separate them from the grains of sand; the mixture is thus immediately analyzed.

very

diffi

Mix common salt and sand;-it would be cult, almost impossible, to separate, or to pick out, their individual grains, even if the eye were aided by a magnifier; and, as mechanical means fail, chemical means must be tried.

Experience teaches us that salt will dissolve in water, and that sand will not: therefore if water be added to this mixture, and agitated, and poured off, and more water added and agitated, and again poured off, until it has no saline taste, the sand will remain, and by placing the solution of the salt in a warm oven, the water, or the chemical solvent, will dry away, and leave the salt. This is a simple example of analysis.

Mix common salt, sand, and sawdust,-how are these to be separated? Add water to dissolve the salt;-the sand will subside, but the sawdust will float, or remain. suspended in the solution; and if this be poured upon a fine sieve, the sawdust will remain, whilst the solution passes through, and the salt can be obtained from it as before. This is another example of analysis.

The chemist, therefore, by extensive knowledge of