812 CLAY. 
its own intrinsic composition, and upon the geor- 
gic treatment which it has received. Every clay 
soil which contains too large a proportion of 
alumina, or which is unduly fine, soft, and unctu- 
ous, is over-tenacious, compact, and adhesive, and 
requires to be improved, both in its mechanical 
texture, by an intermixation of siliceous sand or 
gravel, and in its chemical character, by the ad- 
dition of farm-yard and calcareous manures. 
Coarse, moorish clay lands, of the class so well 
known in Scotland under the name of till, con- 
tain a comparatively large proportion of the 
oxides of iron, and are of a hard and obdurate 
nature, and require a large amount of working, 
manurirg, draining, and exposure, in order to be 
reclaimed from their stubbornness, and reduced 
to fertility. 
Burnt clay is, in some districts of England, ex- 
tensively used and highly extolled as a fertilizer 
of several kinds of soils, and particularly of such 
as are too retentive, and require to be rendered 
porous and friable, See the article Asuzs. The 
beneficial action of so seemingly incongruous a 
manure as mere burnt clay or calcined argilla- 
ceous earth, is usually ascribed to the insolubility 
which the clay has acquired from calcination, 
and to its consequent similarity of mechanical 
power to that of siliceous sand; but the true 
cause, according to Liebig, is the following :— 
“Peroxide of iron and alumina are distinguished 
from all other metallic oxides by their power of 
forming solid compounds with ammonia. The 
precipitates obtained by the addition of ammonia 
to salts of alumina or iron are true salts, in which 
the ammonia is contained as a base. Minerals 
containing alumina or oxide of iron also possess, 
in an eminent degree, the remarkable property 
of attracting ammonia from the atmosphere, and 
of retaining it. Vauquelin, whilst engaged in 
the trial of a criminal case, discovered that all 
rust of iron contains a certain quantity of am- 
monia. Chevalier afterwards found that ammo- 
nia is a constituent of all minerals contaifling 
iron; that even hematite, a mineral which is not 
at all porous, contains one per cent. of it. Bouis 
showed also, that the peculiar odour observed on 
moistening minerals containing alumina, is partly 
owing to their exhalingammonia. Indeed, many 
kinds of gypsum and some varieties of alumina, 
pipe-clay for example, emit so much ammonia, 
when moistened with caustic potash, even after 
they have been exposed for two days, that red- 
dened litmus paper held over them becomes blue. 
Soils, therefore, containing oxides of iron and 
burnt clay must absorb ammonia, an action which 
is favoured by their porous condition; they fur- 
ther prevent, by their chemical properties, the 
escape of the ammonia once absorbed. Such 
soils, in fact, act precisely as a mineral acid 
would do, if extensively spread over their sur- 
face. The ammonia absorbed by the clay or fer- 
ruginous oxides is separated by every shower of 
rain, and conveyed in solution to the soil.” 
CLAYTONIA. 
But one large proportion of the calcined or in- 
cinerated matter which the English farmers use 
as manure is in a great degree calcareous; and 
another large proportion contains a somewhat 
bulky admixture of vegetable ashes,—the resi- 
duum of the combustion of grasses, sedges, rushes, 
shrubs, and all sorts of rank and weedy vegeta- 
tion dug up from the borders of fields, the sides 
of hedges, and the scourings of ditches; and the 
former of these kinds of burnt matter operates on 
soil in a manner similar to calcareous marl, while 
the latter exerts a direct and mighty power of 
precisely the same nature as the ashes of wood 
or turf. In all manuring with what is popularly 
termed burnt clay, close and judicious regard. 
should be had both to the precise nature of the 
material itself, and to the particular defect or 
needs of the land to which it is applied. The 
treating of all sorts of burnt clayey-looking earth 
or sward as of one nature, and the indiscriminat- 
ing application of it to all lands of clayey charac- 
ter, without reference to exigency or mode of 
action, are practices totally unworthy of the en- 
lightenment of the nineteenth century, and ex- 
ceedingly likely to issue in a greater or less de- 
gree of disappointment. 
Native, unburnt clay, especially such as is 
highly aluminous, is the best possible material 
for improving light, arid, sandy soils, and white, 
gravelly, hungry, moorish lands. But it requires 
to be so prepared and applied as to enter into 
ready and complete incorporation with the soil; 
for if it lie in lumps and masses, it will speedily 
be washed into solution with rains, and carried 
by infiltration to the bottom, there to form a re- 
_tentive subsoil, and render the land cold, sour, 
and worse in quality than before. A good method 
of securing its incorporation, is to lay it on the 
land, while the latter is in grass, and is about to 
be broken up for tillage or fallow,—to permit it 
to lie exposed on the grass, till it becomes dried. 
and pulverized by the action of winds and frosts 
and general weather,—to divide and scatter it by 
repeated slight harrowings,—and, after it is thor- 
oughly distributed and well pulverized, to turn 
it into the soil by an ordinary ploughing. About 
50 tons per acre may, on the average, be a proper. 
quantity for deep, fine, alluvial, sandy soil, and 
probably 150 tons for white, gravelly, moorish 
land.—Lyell’s Geology.— Beatson’s New System of 
Cultivation.—Liebig’s Chemistry of Agriculture — 
Sir John Sinclatr’s General Report of Scotland.— 
Reports to the Board of Agriculture—Journal of 
the Royal Agricultural Society of England. — 
Rham’s Dictionary of the Farm—Bradley’s Hus-- 
bandry. 
CLAYTONIA. A genus of hardy, ornamental, 
herbaceous plants, of the purslane tribe. The 
Virginian species, C. virginica, was brought to 
England by a Mr. Clayton, about the middle of 
last century. Its root is tuberous; its stems are 
slender, and from 3 to 6 inches high; its leaves 
lare succulent, deep-green, narrow, and about 2 
