SPECIES OE INO RG AN IC MANURES. 425
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attracts carbonic acid from the air ; and the animal or vegetable matters decompose by
degrees, and furnish new products as vegetable nourishment. In this view, lime presents
two great advantages for the nutrition of plants ; the lirst, that of attracting nutritious
gases from the air ; the second, that of jtrolonging the action and nutritive qualities of
organic substances, beyond tlio term during which they wonld be retained if these substances
were not made to enter into combination with lime. Thus the nutritive qualities
of blood, as it exists in the compound of lime and blood known as sugai-bakcr’s scum,
are moderated, prolonged, and given out by degrees ; blood alone, applied dfrectly to
the roots of plants, will destroy them with few or no exceptions.
1312. Different kinds o f limestones have différent effects. The limestones containing
alumina and silica are less fitted for the pm-poses of manure than pure limestones ; but
the lime foimed from them has no noxious quality. Such stones are less efficacious,
merely because they contain less lime, and because they are apt to harden or vitriiy
in burning, and then do not fall to pieces well hy slaking when spread over the land.
There is very seldom any considerable portion of coaly matter in bituminous limestones
; never as much as five pai-ts in 100 ; but such limestones make very good lime.
The carbonaceous matter can do no injury to the land, and may, under certain circumstances,
become the food of the plant. Some limestones and kinds of chalk or marl
contain a small proportion of phosphoric acid, and are in consequence valuable manures.
1313. Magnesian limestone, though it has been found in a pure state to injure
crops, has yet been used with good effects in some cases. Magnesia has a much weaker
attraction lor carbonic acid than liinie, and will remain in the state of caustic or calcined
magnesia for many months, though exposed to the air ; and, as long as any caustic Ihne
remains, the magnesia cannot be combined with carbonic acid, for lime instantly attracts
carbonic acid from magnesia. When a magnesian limestone is burnt, the magnesia is
deprived of carbonic acid much sooner than the lime ; and, if there is not much vegetable
or animal matter in the soil tq supply by its decomposition carbonic acid, the magnesia
will remain for a long while in the caustic state, in which state it acts as a poison to
certain vegetables ; and that more magnesian lime may be used upon rich soils, seems to
be owing to the circumstance, tliat tlie decomposition of the manm-c in them supplies
carbonic acid. Magnesia in its mild state, i. e. fully combined with carbonic acid, seems
to be always an useful constituent of soils. I t is obvious, from what has been said, that
lime ii-om the magnesian limestone may be applied in large quantities to peats ; and that
where lands have been injured by tlic application of too large a quantity of magnesian
lime, peat will be a proper and efficient remedy.
1314. Limestones which contain magnesia effervesce with acids less freely than those
which contain none; they are also gcneraliy known by the presence of numerous
minute black dots all oi'er the surface of the stone. From the analysis of Tennant, they
appeal- to contain from 20-3 to 22-5 magnesia; 29-5 to 31-7 lime ; 47-2 carbonic acid ;
0-8 clay and oxide of iron. Magnesian limestones are usually of a brown or pale yellow
colom-. They are found in Somersetshire, Leicestershfre, Derbyshire, Sln-opsliire,
Durham, and Yorkshire ; and in many parts of Ii-cland, particularly near Belfast. In
general, when limestones arc not magnesian, their purity wiU be indicated by their loss
of weight in burning ; the more they lose, the larger is the quantity of calcareous matter
they contain. The magnesian limestones contain more cai-honic acid than the common
limestones ; and all of them lose more than half thcir weight by calcination.
1315. Gypsum. Besides being used in the foi-ms of lime and carbonate of lime, calcareous
matter is applied as manure in other combinations. One of these bodies is
gypsum, or sulphate of lime. This substance consists of sulphuric acid (the same body
that exists combined with water in oil of vitriol) and lime ; and when dry, it is composed
of forty-two parts of lime and fifty-eight pai-ts of sulphuric acid. Common gjqjsum, or
selenite, such as that found at Shotovcr Hill, near Oxford, contains, besides sulphuric
acid and lime, a considerable quantity of water ; and its composition may be thus expressed
: sulphm-ic acid forty-nine parts ; lime thirty-six pai-ts ; water fifteen pai-ts in
a hundred.
1316. The nature o f gypsum is easily demonstrated : if oil of vitriol be added to
quicklime, there is a idolent heat produced ; when the mixture is ignited, water is given
off, and gypsum alone is the result, if the acid has been used in sufficient quantity ; and
gypsum mixed with quicklime, if the quantity has been deficient. Gypsum, free from
water, is sometimes found in nature, when it is called anhydrous selenite ; it is distinguished
from common gypsum by giving off no water when heated. Wlien gypsum,
free from water, or deprived of water by heat, is made into a paste with water, it rapidly
sets by combining with that fluid. Plaster of Pai-is is powdered dry gypsum, and its
property as a cement, and its use in making casts, depend upon its solidiiying a certain
quantity of water, and making with it a colicrcnt mass. Gypsum is soluble in about 500
times its weight of cold water, and is a little more soluble in hot water. I t is commonly
found in spring water, which in part owes its hardness to tho presence of this
salt. _ Gypsum is easily distinguished by its properties of affording precipitates to
solutions ot oxalates and of barytic salts. I t has been much used in America, where it
was first introduced by FrankUn on his rctui-ii from Paris, where ho had been much
struck with its effects. He sowed the words. This has been sown with gypsum, on a field
ot luccrn, near Washington ; the effects astonished every passenger, and the use of the
manure quickly became general, and signaUy efficacious. I t has been advantao-eously
used 111 Kent, but in most counties of England it has failed, though tried in varioirs ways
and upon different crops. *
1317. The ashes o f saintfoin, clover, and rye-grass, afford considerable quantities o f
ppsum ; aud that substance probably foims a necessary part of thcir woody fibre.
This may be the reason why it operates upon gi-ass land in such smaU quantities ; for
the whole of a clover crop, or saintfoin crop, on an acre, according to estimation, would
afford by incineration only three or four bushels of gypsum. The reason why gypsum
IS not always efficacious, is probably because most cultivated soils contain it in sufficient
quantities for the use of the grasses. In the common com-se of cultivation, gypsum
IS ftiniished in the manure ; for it is contained in stable dung, and in the dung of all
cattle fed on gi-ass : and it is not taken up in com crops, or crops of peas and beans, and
in vei-y small quantities in turnip crops ; but where lands are exclusively devoted to
pasturage and hay, it will he continually consumed.
1318. Phosphate o f lime is a combination of phosphoric acid and lime, one proportion
of each. I t is a compound insoluble in pm-c water, but soluble in water containing any
acid matter. I t foims the greater part of calcined bones. I t exists in most excremen-
titious substances, and is found both in the straw and grain of wheat, barley, oats, and
rye, and likewise in beans, peas, and tai-es, and in the ashes of most Idnds of wood. I t
exists in some places in these islands native, but only in vei-y small quantities. Phosphate
of lime is generally conveyed to the land in the form of bones, but it also enters into
the composition of all other organic manures.
1319. There are various other compounds o f lime which arc found in particular
soils. Amongst these is the nitrate of lime, a white salt, easily soluble in water and
readily formed by acting on lime or its cai-bonate by nitric acid. I t is also formed
. whenever organic matters containing nitrogen arc suffered to putrefy in contact witli
lirac ; when animal manure and lime are left together, nitrate of lime is formed • the
same salt is frequently found in the mortal- of old walls, particularly those of stables’ and
similai- outhouses. When mixed with a solution of carbonate of potasli, both salts are
decomposed. Muriate of lime is foi-med from lime and muriatic acid, and is remarkable
for its ^ e a t attraction for water. I t exists in sea water, and consequently is
often found in common salt. A small quantity of tliis salt appears to be formed by
the action of lime on common salt. Mixed -with a solution of carbonate of ammonia,
both salts ai-e decomposed, chalk and muriate of ammonia being formed ; this is
remarkable, because those two salts, when mixed together dry and heated, form muriate
of lime and cai-bonate of ammonia.
1320. The saline compounds o f magnesia will require very little discussion with regard
to their uses as manures. In combination with sulphuric acid, magnesia forms a soluble
salt, well known under the name of Epsom salts. This substance has been found of
use as a manui-c ; but it is not found in nature in sufficient abundance, nor is it capable
of being made by ai-t sufficiently cheap, to be of useful application in the common course
of culture.
1321. Wood-ashes. Wlicn wood, or, indeed, any vegetable matters are burnt, various
chemical changes are produced, provided they are exposed to the action of the air while
combustion is taking place. When this is the case, as Liebig ohsei-vcs, “ the carbon of
these substances is converted into carbonic acid, their hydrogen into water, their nitrogen
is set at liberty in the form of ammonia, aud thcir sulphur assumes the form of sulphuric
acid, so that at last nothing remains except the mineral ingredients of these substances
iu the form of ashes.” (Liebig’s Chemistry, ^c., 4th ed., p. 175.) These ashes, therefore,
contain all the salts required for the food of plants.
1322. Soda is found in the ashes of sea-weed, and may be procm-ed hy certain chemical
agencies from common salt. Common salt consists of the metal named sodium,
combined with chlorine ; and pure soda consists of the same metal united to oxygen.
When water is present, which can afford oxygen to the sodium, soda may be obtained
in several modes from salt. The same reasoning will apply to the operation of soda and
its compounds, as of the other alkalies and salts ; and when common salt acts as a
manure, it is probably by supplying inorganic matter to the plant in the same manner
as gypsum, phosphate of lime, and the alkalies. In small quantities it is sometimes a,n
useful manure, and it is probable that its efficacy depends upon many combined causes.
I t is not unlikely, that the same causes as those which act in modifying the operation of
gyjisum influence the effects of salt. Most lands in these islands, pai-ticularly those near
the sea, probably contain a sufficient quantity of salt for all the piu-poscs of vegetation ;