424 
I'HE TROPICAL AGRICULTURIST. 
[December i, iSqi. 
We do not, therefore, need to add carbon to the 
soil. However, as wo shall notice later, some forms 
of carbon possess value as indirect fertilizors. 
HYDROGEN. 
28. Occurrence in Nature. — The element, hy- 
drogen, is nearly always found nncoinbiued witli other 
element. It combines with oxygen to form water. 
Hydrogen also occurs in most animal and vegetable 
auDstancea, such aa various kinda of wood, fruits, 
etc., when it is combined with tho elements, carbon 
and oxygen. Hydrogen is always present in all kinds 
of acids. 
29. Description of Hvdrooen. — Hydrogen, in Uie 
unconibined form, ia a gas that resembles air in that 
it has neither color, anieli, nor tasto. 
OXYGEN. 
30. Occurrence OF OxYOF.N IN Nature. — Oxygen is 
the moat abundant of all the elements. Tho com- 
S ounda which contain no oxygen are few in number. 
►xygon forma nearly one-half of the crust of tho 
earth; eight-ninths of water; about one-fifth of air, 
and one-third of all animal and vegetable matter. 
Oxygen occurs in tho air unconibined with other 
elements. Oxygen, combined with tho elements car- 
bon and hydrogen, or with carbon, hydrogen and 
nitrogen, ia found in aubstances which go to make up 
animals and vegetables. 
31. Description op Oxygen. — A.s might be inferred 
from knowing that oxygen in tlie unconibined 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 
tho other elements, la ail forms of burning, the 
oxygen of tho air is simply uniting with other ele- 
ments. Thus, in a coal tire tho oxygen unites with 
tho carbon of the coal. Tho heat is produced by 
ho union of the two. 
THE RELATIONS OF HYDROGEN AND OXYGEN 
TO FERTILIZERS. 
32. As already stated, water ia formed by tho union 
of two gasea, hydrogen and oxygen. Thcao 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 tho hydrogen and oxygen 
wiiich they need to build up their tissues. In this 
manner water acta as a direct fertilizer. Tho water 
is supplied by rains to tho aoilf from tho soil it is 
taken into the plant through the roots. In regions 
adapted to agriculture, plants receive all the hydrogen 
and oxygon needed, and usually much more, from 
the rains. Therefore, these elornenta 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 phiiits by irrigation, it 
can very properly be called a fertilizer, and an ex- 
tremely important one, too. 
35. In addition to its action as a direct fertilizer, 
water has an iiuporta .t part to play as an in liroct 
fertilizer. Thus, It dissolves tho soluble food materials 
of tho soil, tho mineral matter and most of tho 
nitrogen, and carries them into the plant. In addition 
to its action aa an indirect fertilizer, water acts as 
a carrier within tho plant in transferring from one 
part of the ^ilant to another, as needed, the various , 
products contained in the plant, just as tho blood 
in the animal body carries to every part tho nutri- 
ment adapted to each organ and part. 
NITROGEN. 
31. Occurrence op Nitrogen.— Nitrogen occurs in 
nature in the following foms;— 
(1). As a constituent of air. 
(2). In the fonnof ammonia. 
(3). In tho form of nitric acid and nitrates. 
(4). lu various other forms in plants and animals. 
35. Nitrogen in Air.— Nitrogen, unconibined with 
other elements, forms about four-fifths of the air, ! 
Since the nitrogen in the tvir is not cowhiuod, w'O j 
can conceive its properties for ourselves, and ou 
observations show us that it ia a gas, which has 
neither color, tasto, nor smell. 
30. Nitrogen in Ammonia. — Nitrogen combined 
with the element hydrogen forms ammonia. Ammo- 
nia is present iu the air in very sinall quantities. 
Amuioiiia is formed when vegetable and animal sub- 
Btaiiecs containing nitrogen dccompoBe. 
Ammonia is a colorless gas, and it is this gas dis- 
solved iu water which ia faiiiilar 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 wo call anmionium 
salts, compounds w’hich do not generally have any 
odor like ammonia. Tlius, ammonia combined with 
sulphuric acid forms ammonium sulpliate, called by 
some, sulphate of ammonia. Ammonia combined with 
hydrochloric acid forms auiinonium chloride, some- 
• times called iniiriato of ammonia, also known as sal- 
ammoniac. 
37. Nitrogen in Nitrates. — Nitrogen, combined 
with hydrogen and oxygen, forms nitric acid ora^mi 
/orfiif. If in nitric acid aiuotal, as sodium, for example, 
takes tho place of hydrogen, w'e have a sodium salt of 
nitric acid, or a nitrate, formed, called sodium nitrate. 
When animal or vegetable substances deconipose in 
rather warm, moist places, the nitrogen is changed 
into nitrates. This change of the nitrogen of organic 
matter into nitrates is caused hy bacteria, whicn are 
very sinallliving vegetable organisms, and which exist 
everywhere in enormous numbers. The process is 
known as “nitrification.” 
.38. Nitrogen in Animals and Plants, on, Or- 
ganic Nitrogen. — Nitrogen, combined with the ele- 
ments, hydrogen, carbon and oxygen, occurs in plants 
and in antniaU. Such Bubstancos, for example, are 
tho casein or curd 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. Tho 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 : — 
fl). As nitrogen gas or uiicombiiiod nitrogen. 
(2l. In tho form of ammonia. 
(3). In the form of nitrates. 
All plants cannot use nitrogen in any of these throe 
forms equally well, but each form is found specially 
suited to certain kinds of plants, as will be iioiicca. 
40. Nitrogen Gas used ry Plants. — Although wo 
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 iilants which 
are called leguminous, such os tlie bean, pea, clover, 
alfalfa, etc., can take uncombined nitrogen from the 
air. 
41. Nitrogen of Ammonia used by Plants, — The 
leaves of ^mo plants liave the power of absorbing 
ammonia directly from the air and obtain nitrogen 
in this way. Some plants obtain nitrogen from am- 
nioniura salts through the soil. 
42. Nitrogen of Nitrates used by Plants. — The 
largest part of the nitrogen wliich 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 potasBium. Ab 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 process called 
nitrification. Hence, nitrogen, in the form of nitrates, 
is the most available form for most plants; that is, 
it can ho most readily taken up and used by plants. 
RELATIONS OF NITROGEN TO I'EIiTILIZEES. 
'13. Experiments have shown that nitrogen ia es- 
sential to tho growth of plants; that the quantities 
of nitrogen aYailable as plant footi are very small ; 
