Common potters’ clay, or pipe-clay, diffused through water, and added to milk of lime, thickens immediately upon mixing; and if the mixture is kept for some months, and then treated with acid, the clay becomes gelatinous, which would not occur without the admixture with the lime.  The lime, in combining with the elements of the clay, liquifies it; and, what is more remarkable, liberates the greater part of its alkalies.  These interesting facts were first observed by Fuchs, at Munich:  they have not only led to a more intimate knowledge of the nature and properties of the hydraulic cements, but, what is far more important, they explain the effects of caustic lime upon the soil, and guide the agriculturist in the application of an invaluable means of opening it, and setting free its alkalies—­substances so important, nay, so indispensable to his crops.

In the month of October the fields of Yorkshire and Oxfordshire look as it they were covered with snow.  Whole square miles are seen whitened over with quicklime, which during the moist winter months, exercises its beneficial influence upon the stiff, clayey soil, of those counties.

According to the humus theory, quick-lime ought to exert the most noxious influence upon the soil, because all organic matters contained in it are destroyed by it, and rendered incapable of yielding their humus to a new vegetation.  The facts are indeed directly contrary to this now abandoned theory:  the fertility of the soil is increased by the lime.  The cerealia require the alkalies and alkaline silicates, which the action of the lime renders fit for assimilation by the plants.  If, in addition to these, there is any decaying organic matter present in the soil supplying carbonic acid, it may facilitate their development; but it is not essential to their growth.  If we furnish the soil with ammonia, and the phosphates, which are indispensable to the cerealia, with the alkaline silicates, we have all the conditions necessary to ensure an abundant harvest.  The atmosphere is an inexhaustible store of carbonic acid.

A no less favourable influence than that of lime is exercised upon the soil of peaty land by the mere act of burning it:  this greatly enhances its fertility.  We have not long been acquainted with the remarkable change which the properties of clay undergo by burning.  The observation was first made in the process of analysing the clay silicates.  Many of these, in their natural state, are not acted on by acids, but they become perfectly soluble if heated to redness before the application of the acid.  This property belongs to potters’ clay, pipe-clay, loam, and many different modifications of clay in soils.  In their natural state they may be boiled in concentrated sulphuric acid, without sensible change; but if feebly burned, as is done with the pipe-clay in many alum manufactories, they dissolve in the acid with the greatest facility, the contained silica being separated like jelly in a soluble state.  Potters’