V 
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THE CHEMISTRY OF SOILS AND MANURES. 
Nitrate of potash, or saltpetre — a combination of nitric acid with, potash — is occasionally found in 
small quantities in richly-manured garden land, and occurs naturally in certain districts in India, 
where it is found so abundantly that the salt forms a white efflorescence on the surface of the soil. 
2. Soda. — Sea-weeds and plants growing near the sea-shore, on combustion, produce an ash, which 
contains much soda. The soda is as essential to sea-plants as potash is to land-plants. 
Soda, like potash, is not a simple or elementary body, but a combination of a white metallic 
substance — sodium, with oxygen, and in many respects resembles potash. Pure or caustic soda is 
obtained in the same manner as caustic potash, from carbonate of soda — a combination of carbonic acid 
with soda, known to most persons under the more familiar name of common washing soda. Carbonate 
of soda occurs in the soil in many warm climates (Egypt, India, South America, &c), in so large 
quantities that it is technically prepared in these places by washing the soil with water, and evaporat- 
ing the washings until the soda begins to separate in crystals. In our own land, carbonate of soda is 
rarely found in any large quantity naturally, and its presence in the soil often may be traced to the 
water with which the land, naturally or artificially, is irrigated. Deep well-waters in limestone 
districts usually contain carbonate of soda, which therefore would appear to exist in many limestones. 
I have myself found traces of carbonate of soda in the soil of the College farm, as well as in all the 
oolitic rocks of the neighbourhood, and in the pump-water of Cirencester. 
By far the most common form in which soda occurs in soils is as common salt. Chloride of sodium, 
common or sea-salt — a combination of chlorine-gas with sodium — may easily be detected in all soils of 
England, and prevails particularly in localities which are known to have once been the beds of ancient 
seas, or in lands which are much exposed to sea-breezes. With the spray common salt is often carried 
by the wind to very considerable distances inland, and it is perhaps the neighbourhood of the sea 
which explains why common salt does not produce the same striking effects on vegetation in this 
country which we observe to follow the application of sea-salt on the Continent. All maritime plants 
require much common salt as a necessary clement, without wliich they must perish ; and we safely 
infer therefrom, from the occurrence in inland localities of the Sea-pink (Armcria maritima), the Sea- 
plantain (Plantago maritima), the Salt-wort (Glaux maritima), the Sea-sandwort (Arcnaria marina), 
and other plants which delight to grow by the sea-side, that the soil in these places always contains 
much common salt. In good garden land, and in fields near towns, common salt is generally found in 
larger proportions than in soils remote from the sea -shore. 
Nitrate of soda, or Chili, or cubical saltpetre, is a salt consisting of nitric acid and soda, which is 
imported largely into this country, chiefly from Cliili and Peru. It is used extensively for technical 
and agricultural purposes. In Chili and Peru it occurs native, forming frequently extensive beds. In 
our own country, nitrate of soda is found now and then in richly manured land, and appears to exercise 
a most marked effect on grass land. Even a very small dose of nitrate of soda applied to pasture or 
artificial meadows causes the more luxuriant growth of the herbage, and gives a peculiar rich darker 
green appearance to the meadows thus treated. 
Sulphate of soda, or Glauber suit, which is found in many mineral springs, is occasionally met with 
in soils ; but, on the whole, it is not a constant element of all soils. 
Silicates of soda — combinations of silica with soda — in every respect resemble their- corresponding 
potash salts. Silicate of soda, in small quantities, is found in most soils. 
3. Lime. — Chalk, marble, limestone, are the names of some varieties of carbonate of lime. These 
minerals are, more or less, pure forms of carbonate of lime, and are found in nature often in enormous 
masses, spreading over hundreds of acres. Exposed to the heat of a lime-kiln, the carbonic acid is 
driven out by the intense heat, and pure or caustic lime remains in the kiln. Caustic lime, prepared 
from white marble, the purest form of carbonate of lime, is a perfectly white' substance, which is com- 
posed of the metal calcium, and oxygen gas. 
In its effects on vegetable and animal matters, caustic lime resembles caustic potash and soda ; but 
it is much slower in its action. Caustic or quick lime, on account of these elfects. is therefore \ised 
with much benefit on peaty land. The excess of organic matter, wliich acts injuriously on vegetation, 
is thereby gradually destroyed or converted into really nutritious food for plants. Quick lime, Sprinkled 
with water, absorbs the same with evolution of much heat, and falls to powder, or becomes slaked. 
Slaked lime, a white powder, though perfectly dry to all appearance, contains much water in an 
invisible form; the water is chemically combined with lime, ami this compound, in everyday life, 
called slaked, is termed by the chemist lime-hydrate. If slaked lime i- exposed to air, it att 
carbonic acid from the atmosphere, and becomes partially changed into mild, ot carbonate of, lime. 
Caustic lime is slightly soluble in water, which thereby is rendered alkaline. Lime-water is a solution 
of lime in water. Carbonate of lime, on the contrary, is scarcely soluble in perfectly pure water : but 
