Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/21

Rh  the catalogue of tipplers, rather than to promote the purposes of health.  CLAY is a compact, heavy, stiff, viscid, and ductile earth, when moist, which is easily dissolved, and, when mixed with water, does not readily subside.

For promoting the vegetation of many plants, clay is a necessary ingredient in the soil, with the exception of those species called argilla aërata, or lac lunæ, and argilla apyra, or porcelain, and other white, fermenting clays, for which no use has hitherto been discovered in agriculture. By its cohesion, clay retains humidity, on which, perhaps, its fertilizing property chiefly depends.

In its pure state, clay is unfit for the purposes of vegetation, on account of the great adhesion of argillaceous particles, which cannot be penetrated by the tender fibres of roots; but, when mixed with calcareous earth, and siliceous sand, or marl, it is much improved, and of great use in tillage.

It is commonly believed, that lumps of clay, in a moist state, may be rendered more friable, by exposing them to frost; which, by expanding the water they contain, and converting it into ice, is supposed to cause a farther separation of the clayey particles. This notion, however, appears to be erroneous; for, unless the frost be very sudden, it will probably be attended with a contrary effect. Mr. observes, that clay, in its dry state, absorbs more than twice its weight of water, before it parts with that fluid, and retains it, in the open air, more tenaciously than other earths; but, in a freezing cold, clay contracts more, than other soils, and, as it were, squeezes out its water in a greater than usual proportion.

As clay, by the great cohesion of its particles, is not well adapted to the growth of roots, Dr. remarks, that it may, in some degree, be corrected, by frequently exposing the air confined in its interstices; for instance, by turning it over with the plough, or spade. Another method is, by planting, in a clayey soil, first, those vegetables which are known to thrive in it, such as beans; and if their roots be afterwards left to putrify in the clay, they render the mass less cohesive, and enrich, rather than impoverish, the land. When clay abounds with vitriolic acid, so as to be convertible into alum, it becomes very unfavourable to vegetation, and checks the growth of trees, as well as of herbaceous plants, by corroding the fine extremities of their roots. This injurious quality may be most effectually remedied, in gardens, by wood-ashes, or soap-suds; and, in fields, by mixing with such clay, lime, powdered chalk, or the sweepings of roads consisting of lime-stone.

, are those which abound with clay, whether black, blue, white, &c.; of which, the black and yellow are the best for corn.

All clay soils, as they retain too much water, are apt to chill the plants in moist seasons; on the contrary, in dry weather, they become hard, and obstruct vegetation. They naturally produce weeds, goose-grass, thistles, poppies, &c.; but some will yield clover and rye-grass; and, if well manured, bear the best grain. Such soils are more advantageously manured than any other lands: the most proper that Rh