hill does not throw off, in its first fermentation, any of the most i-aluable and the most
efficient parts of the dung, but chiefly vapour of water ; and that, though when the
texture of tlio fibrous part of farm-yard manure begins to decompose, there will be au
evolution of some of the gases which constitute the food of plants, no haim accrues to
the dung as a manure from the escape of these gases. Sir Humphry D a iy supposed that
these gases constituted tlie food of plants, and that, if they were pennitted to be dissipated
by decomposition, the quantity of nourisliment in the heap of manure wonld of
course be so much diminished ; that if the bulk of the dung-hcap be diminished one
half, or one third, by excessive fermentation, the quantity of nourishment to the crops
would he diminished in a greater ratio ; but practical men contended, that, though some
of the gases wliich constitute the food of plants are disengaged from fermenting stable
manure, yet that it does not follow that plants wül receive them as food directly they
arc disengaged. On the contraiy, it is considered that they would either reject ibod in
that state or, if they could not avoid taking it in, that they wonld be injured by it.
“ Accordingly, we invariably find that plants suffer from their contact with fermenting
dung, and it is this well-known fact, more than any other circumstance, which deters
garilcners from applying dung in an unprepared state.” What has experience determined
as the least iiijm-ious state in which dung can be applied to any crop ? The
cultivator answers, in the state of short muck, that is, as “ a soft cohesive mass,” capable
of being cut by a spade ; and this is now proved hy science to he the state in wliich it
is best suited to afford plants their proper food.
Sect. II. O f Inorganic Manures.
1299. Inorganic manures consist of those mineral substances which are added to the
soil iu order to supply the earthy and saline matters which arc required by soils to render
them suitable for the growth of certain plants.
Stibsect. 1. The Theory o f the Operation o f Inorganic Manures.
1300. Various earthy and saline swôsiances have been proved to constitute an important
part of the food of plants, and it has also been proved that different plants not only
require different kinds of these substances, but also that they are found in some soils and
not in others. Thus if plants requiring phosphate of lime are groivn in a soil which
does not contain that salt, they become weak and unhealthy ; but if phosphate of lime
could be added to the soii artificially, it would instantly become so changed in its nature
that the plants which before would scarcely live in it will gi-ow luxuriantly.
1301. Earthy matters, it is fomid, are not taken up by plants in a pure state, but
generally in the form of salts, and also that several kinds of earth are i’omid in every
plant.
1302. Salts are formed by the combination of an acid with an alkaline base, and there
are various kinds according to the substances of which they are composed.
1303. The principal earths which combine with acids to form the salts necessary fo r
vegetables are lime, magnesia, and alumina, the two former being called alkaline earths ;
and tbe principal alkalies are potash, soda, and ammonia.
1304. The more important acids are carbonic acid, phosphoric acid, nitric acid, sulphuric
acid, and muriatic acid, the first four of which are formed by combinations
between the element from which they derive thcir name and oxygen ; whilst the latter
is a compound of chlorine and hydrogen.
1305. The fa c t that earthy and saline matters were different in different plants yras
known to the earlier vegetable physiologists, though they do not appear to have drawn
any practical deductions from the facts they ascertained. Jacquin states, that the ashes
of glass-wort (Salsôla Sòda), when it grows in inland situations, afford the vegetable
alkali ; bnt when it grows on the sea-shore, where compounds which afford the fossil
alkali are more abundant, the ashes yield that substance. Du Hamel found that plants
which xisually grow on the sea-shore made small progress when planted in soils containing
little common salt. The sun-flower, when growing in lands containing no nitre,
does not afford that siibstance ; though, when watered by a solution of nitre, it yields
nitre abundantly. The tables of De Saussure show that the ashes of plants are similar
in constitution to the soils in which they have vegetated. De Saussure made plants
grow in solutions of different salts ; and he ascertained that, in all cases, certain portions
of the salts were absorbed by the plants, and found unaltered in their organs. Even
animals do not appear to possess the power of forming the aUcaline and earthy substances.
Dr. Fordyce found th a t when canary birds, at the time they were laying eggs,
were deprived of access to carbonate of lime, their eggs had soft shells ; and the same
result, from a similar cause, has been obseiwed in the eggs of common domestic fowls.
1306. I t is now clearly ascertained that the earthy and saline substances found in plants
iu*e as essential as any other pai’t of thcir food, and that if any soil be deficient in the
subsiances of tliis nature wliicli are required by tho plants which are to be grown in it
w T L tn s L " t o r " ‘“ft “ "'“ ft“ ‘“ft ft"“' " frftfift""
Subsect. 2. O f the different Species o f Inorganic Manures.
. T T geuerahy considered to include the alkalies with their compounds. alkaline earths and
1308 Lime is the most important of the alkaline earths. The most common form in
V fiicii It IS iound IS in a state ot combination with cai-bonic acid or fixed air I f a uiece
of limestone or chalk be thrown into an acid liquid, there wiU be an eticn-escence. This
IS owing to the escape of the carbonic acid gas. The lime becomes dissolved in the
liqiior. When limestone is strongly heated, the carbonic acid gas is expelled and then
nothing remains but the pure alkaline earth : in this case there is a loss of weight • and
li the fire has been very high, it approaches to one half the weight of the stone • hut in
common cases, limestones, if weU dried before biu-ning, do not lose much more th a n ’ 35
to 40 per cent., or from seven to eight pai-ts out of twenty.
1S09. When burnt lime is exposed to the atmosphere, in a certain time it becomes combined
with carbonic acid gas. Qiucklunc, when first made, is caustic and burning to
the tongiic, renders vegetable blues green, and is soluble in water : but when combined
with carbonic acid, it loses ah these properties, its solnbhity, and its taste : it regains its
power of effen'csciiig, and becomes the same chemical substance as chalk or limestone
Very few limestones or chalks consist entirely of Ihne and carbonic acid. The statuarë
mmbles, and certain o fth e rhomboidal spars, are almost the only piu-e species : and the
different properties of limestones, both as manures and cements, depend upon the nature
of the substances contained in the limestone ; for the tra e calcareous clement the carbonate
of hme, is uniformly the same in nature, properties, and effects, and consists of
45 pai-ts of carbonic acid and 56 parts of lime in 100 parts. lYbcn a Ihnestone does
not copiously effervesce in acids, and is sufficiently hard to scratch glass, it contains
siliceous, and probably aluminous earth : when it is deep brown or red, or stroneiv
coloured with any of the shades of broivn or yellow, it contains oxide of iron ; when it is
not sufficiently hai-d to scratch glass, but effeiwesccs slowly, and makes the acid in
which It eff ervesces imlky, it contains magnesia ; and wlicn it is black, and emits a fetid
smcü If rubbed, it contains coaly or bituminous matter. When newly-burnt lime is
exposed to ffie air, it soon falls mto powder : in this case it is called slaked lime : and
the same effect is unmcdiately produced by thi-owing water upon it, when it heats
violently, and the water disappears. Slaked lime is merely a combination of lime
with about one thn-d of its weight of water; i.e. seventy-five parts of lime absorb
twenty-five parts of water, and form a definite compound called by chemists hydrate
of hme ; and when hydrate of lime becomes carbonate of lime by long exposm-e to the air
tlie water is expelled, and the carbonic acid gas takes its place. Lime moistened with
sea-water is more efficacious than common lime.
1310. Zinie is weU known to act chemicaUy on peat bogs, and to produce astouisliing
bcnclita rru c and g-cnume peat bogs contain a considerable quantity of an acid whicli Iws
some affinity to gaUio acid. I t appears to be tliis acid which confers on peat eaitli its
highly antiseptic qualities, and prevents the complete decay of woody fibre in such
situations. When lime, marl, or shell sand is laid as a manure in such soils, the acid is
neutrahscd, and a salt of lime is formed.
1311. General principles fo r applying lime. The solution of the question whether
quicklime ought to be applied to a soil, depends upon the quantity of inert vegetable
matter that it contains. The solution of the question, whether marl, mild Ihne or
powdered limestone ought to be applied, depends upon the quantity of calcareous mattei-
already in the soil. All soils whieh do not effervesce with acids are improved by mild
hme, and ultimately by quicklime ; and sands more than clays, m e n a soü deficient
in calcai-eous matter, contains much soluble vegetable manure, the application of quicklime
should always be avoided, as it either tends to decompose the soluble matters by
uniting to then- carbon and oxygen so as to become mild Ihne, or it combines with the
soluble matters, and forms compounds having less attraction for water than the pure
vegetable substance. The case is the same with respect to most animal manures • but
the operation of the lime is different in different cases, and depends upon the nature of
the ammal matter. Lime forms a kind of insoluble soap with oily matters, and then
gradually decomposes them by separating from them oxygen and cai-bon. I t combines
likeivise with the animal acids, and assists thcir decomposition by abstracting carbonaceous
matter from them combined with oxygen. According to Cliaptd ( Chimie appliquée, &'c.,
voi. 1. p. 153.), hme forms insoluble composts with ahnost all animal and vegetable' substances
that are soft, and thus destroys thcir fermentative properties. Such compounds
however, exposed to the continued action of the air, alter in course of time ; the lime
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