'424 
rm TROPICAL AQRICULTURISI. 
[December i, 1891. 
We do not, therefore, need to add carbon to the 
soil. However, as we shall notice later, some forms 
of carbon possess value as indirect fertilizers. 
HYDROGEN. 
28. OccuRRfiNCE IN NATURE. — The element, hy- 
drogen, is nearly always found uncombined with other 
element. It combines with oxygen to form water. 
Hydrogen also occurs in most animal and vegetable 
substances, such as various kinds of wood, fruits, 
etc., when it is combined vrith the elements, carbon 
<knd oxygen. Hydrogen is always present in all kinds 
of acids. 
29. Description of Hydrogen. — Hydrogen, in the 
uncombined form, is a gas that resembles air in that 
it has neither color, smell, nor taste. 
oxygen. 
30. Occurrence op Oxygen in Nature. — Oxygen is 
the most abundant of all the elements. The com- 
pounds which contain no oxygen are few in number. 
Oxygen forms nearly one-half of the crust of the 
earth ; eight-ninths of water ; about one-fifth of air, 
and one-third of all animal and vegetable matter. 
Oxygen occurs in the air uncombined with other 
elements. Oxygen, combined with the elements car- 
bon and hydrogen, or with carbon, hydrogen and 
nitrogen, is fomrd in substances which go to make up 
animals and vegetables. 
31. Description of Oxygen. — As might be inferred 
from knowing that oxygen in the uncombined state 
forms part of the air, oxygen has no color, taste or 
smell. 
Oxygen is a very active substance from a chemical 
point of view. It tends to unite with nearly all of 
the other elements. In all forms of burning, the 
oxygen of the air is simply uniting with other ele- 
ments. Thus, in a coal tire the oxygen unites with 
the carbon of the coal. The heat is produced by 
he union of the two. 
tee relations of hydrogen and oxygen 
TO fertilizers. 
32. As already stated, water is formed by the union 
of two gases, hydrogen and oxygen. These elements 
are supplied to plants in the form of water. Grow- 
ing plants contain a larger amount of water than of 
any other constituent. The oxygen and hydrogen 
of the water are separated in the plant, and in 
this way plants secure the hydrogen and oxygen 
which they need to build up their tissues. In this 
manner water acts as a direct fertilizer. The water 
is supplied by rains to the soil ; from the soil it is 
taken into the plant through the roots. In regions 
adapted to agriculture, plants receive all the hydrogen 
and oxygen needed, and usually much more, from 
the rains. Therefore, these elements are not con- 
sidered important parts of fertilizers, except, perhaps, 
that it is desirable to have in a commercial ferti- 
lizer as little water as possible. 
When water is supplied to plants by irrigation, it 
can very jn'operly be called a fertilizer, and an ex- 
tremely important one, too. 
35. In addition to its action as a direct fertilizer, 
water has an importa t part to play as an in^lirect 
fertilizer. Thus, it dissolves the soluble food materials 
of the soil, the mineral inatter and most of the 
nitrogen, and carries them into the plant. In addition 
to its action as an indirect fertilizer, water acts as 
a carrier within the plant in transferring from one 
part of the iJant to Jinother, as needed, the various 
products contained in the plant, just as the blood 
in the animal body carries to every part the nutri- 
ment adapted to each organ and part. 
NITROGEN. 
34. Occurrence of Nitrogen. — Nitrogen occurs iu 
nature in the following forms: — 
As a constituent of air. 
(2). In the foi'm of ammonia. 
(3j. In the form of nitric acid and nitrates. 
(4). In various other forms in plants and animals. 
35. Nitiiooen )N Air. — Nitrogen, uncombined with 
other elements, forms about i'our-lifths of the air. 
yince the niU'Ogow in tho air is not combined, wc ] 
. ^ — J, 
can conceive its properties for ourselves, and ou 
observations show us that it is a gas, which ha^ 
neither color, taste, nor smell. 
36. Nitrogen in Ammonia.— Nitrogen combined 
with the element hydrogen forms ammonia. Ammo- 
nia is present in the air in very small quantities. 
Ammonia is formed when vegetable and animal sub- 
stances containing nitrogen decompose. 
Ammonia is a colorless gas, and it is this gas dis- 
solved in water which is familar to us as ammonia 
water, or "spirits of hartshorn," and which causes 
the peculiar odor of "hartshorn." 
Ammonia unites with different acids and forms 
salts, much as acids do; these salts we call ammonium 
salts, compounds which do not generally have any 
odor like ammonia. Thus, ammonia combined with 
sulphuric acid forms ammonium sulphate, called by 
some, sulphate of ammonia. Ammonia combined with 
hydrochloric acid forms ammonium chloride, some- 
times called muriate of ammonia, also known as sal- 
ammoniac. 
37. Nitrogen in Nitrates. — Nitrogen, combined 
with hydrogen and oxygen, forms nitric acid otaqua 
fortis. If in nitric acid a metal, as sodium, for example, 
takes the place of hydrogen, we have a sodium salt of 
nitric acid, or a nitrate, formed, called sodium nitrate. 
When animal or vegetable substances decompose in 
rather warm, moist places, the nitrogen is changed 
into nitrates. This change of the nitrogen of organic 
matter into nitrates is caused by bacteria, which are 
very small living vegetable organisms, and which exist 
everywhere in enormous numbers. The process is 
knovm as "nitrification." 
38. Nitrogen in Animals and Plants, oh, Or- 
ganic Nitrogen. — Nitrogen, combined with the ele- 
ments, hydrogen, carbon and oxygen, occurs in plants 
and in animals. Such substances, for example, are 
the casein or cm-d of milk, the gluten or gummy 
portion of wheat, the fibrin of blood, the white of egg, 
etc. When such compounds decompose, the nitrogen 
is first changed into ammonia, and then, under proper 
conditions, into nitric acid or nitrates. The nitrogen 
existing in animals and plants is generally spoken 
of as organic nitrogen. 
IN WHAT FORMS IS NITROGEN USEFUL TO PLANTS ? 
39. Plants can use nitrogen in three different 
forms, viz : — 
(1) . As nitrogen gas or uncombined nitrogen. 
(2) . In the form of ammonia. 
(3) . In the form of nitrates. 
All plants cannot use nitrogen in any of these three 
forms equally well, but each foi-m is found specially 
suited to certain kinds of plants, as will be noticed. 
40. Nitrogen Gas used by Plants. — Although we 
have nitrogen gas, or uncombined nitrogen, existing 
in the air in enormous quantities, still, the number 
and kinds of plants which can use the nitrogen of 
the air is not large. In general, those plants which 
are called leguminous, such as the bean, pea, clover, 
alfalfa, etc., can take uncombined nitrogen from the 
air. 
41. Nitrogen of Ammonia used by Plants. — The 
leaves of some plants have the power of absorbing 
ammonia directly from the air and obtain nitrogen 
in this way. Some plants obtain nitrogen from am- 
monium salts through the soil. 
42. Nitrogen of Nitrates used by Plants. — The 
largest part of the nitrogen which most plants obtain 
is taken up by their roots from the soil in the form 
of nitrates ; that is, nitric acid combined with some 
metal, as sodium or potassium. As already stated, 
most of the nitrates used by plants are formed by 
changing into nitrates ammonia compounds and or- 
ganic substances in the soil by the X'l-'ooess called 
nitrification. Hence, nitrogen, in the form of nitrates, 
is the most available form for most plants ; that is, 
it can be most readily taken up and used by plants. 
relations op nitrogbn to fertilizers. 
43. Experiments have shown that nitrogen is es- 
sential to tiie growth of plants; that the quantities 
of nitrogen available as plant fpod are very small ; 
