194 : 
which contain potash. It is given subsequently to soils by the growth 
and decaying of vegetable matter. One of the uses, and I have no doubt 
a very important use of potash in a soil, is to assist in dissolving the sand, 
which by this operation, and the assistance of rain water, is melted— 
liquified—dissolved—and in that state is sucked up by the spongy fibre 
of the plant. Clay always contains more or less potash, and as it retains 
moisture, considerably, acts perpetually as a solvent to sand. Lime also 
has considerable solvent action on sand, when in a moist state. Thus 
you perceive that sand with proper auxiliaries, becomes an important food 
for plants, and an excellent friend of man. 
Clay _Next to sand alumina, or clay, is most generally present in soils ; 
though, upon the average, in much smaller quantities than either sand 
or lime. It is the oxyde of the metal aluminum—that is, it consists of 
aluminum and oxygen, in the same way that sand consists of silican and 
oxv^en _or as iron rust consists of the metal iron and oxygen. It is 
found in varying quantities, from one per cent, m a sandy soil, to fifty per 
cent, in a heavy, tough clay soil. Alumina is not found in all plants, 
and only in minute proportion in those in which it does exist. In wheat 
it can liardlv be traced at all; inbarley and rye, 32 ounces only contain 
four o-rains, which is less than the five-thousandth part. It is, therefore, 
apparently of less importance as a direct food for plants, than as an in¬ 
tegral part of a soil necessary to its general fertility. The great use of 
clay appears to be in giving fixity and substance to the sandy particles 
of the soil. In this respect clay is exceedingly beneficial. Many barren 
sandy soils, which would not produce crops at all—indeed, merely shift- 
in o- sands have been converted into fine arable land by spreading clay 
over the sand. Besides the mere mechanical benefit of clay in uniting 
and binding a soil, it is of material service in absorbing and retaining 
moisture. Clay absorbs water more quickly and more abundantly, and 
retains it longer than sand; it does not heat so rapidly as sand, in the 
sun, and it cools again more rapidly, thus helping in hot weather, to 
maintain an equal temperature in the soil. Clay does not become as cold 
as sand in winter, and as frost causes it to contract, it closely embraces 
the roots of plants and prevents their being frozen. Clay lias also pre¬ 
eminently the property of absorbing ammoniacal and other gasses, which 
are generated by decaying manure in the soil. If in a stable from whence 
the strong fumes of the escaping ammonia are issuing, you place a quan- 
