422 
are capable of being united to produce all the differ- 
ent chemical compounds that go to make up the 
countless forms of matter. The number of different 
combinations possible between these seventy elements 
is practically infinite. 
ELEMENTABY COMPOSITION OP PLANTS. 
5. When we state what elements any substance 
contains, we give its elementary composition. For 
example, sugar contains the elements, carbon, hydro- 
gen and oxygen ; this is a statement of the elementary 
composition of sugar. So, when we state what 
elements a plant contains, we give its 
elementary composition or analysis. The term ulti- 
mate composition means the same as elementary com- 
position. We will now consider the elementary com- 
position of plants. 
6. The exact number of different kinds of plants 
growing on the earth has never been definitely ascer- 
tained : but the number probably exceeds 200,000. 
Of this large number, only a few have been subjected 
to careful chemical analysis, and yet, so uniform 
in all its great variety are nature's methods of work- 
ing and building, that we can quite safely say that, 
so far as the elementary composition of plants is con- 
cerned, little remains to be learned. Chemical analysis 
shows that, of the seventy elements known to exist, 
only fourteen are essential to produce all the differ- 
ent forms of vegetable life. 
While all plants contain certain chemical compounds, 
auch as cellulose, albuminoids, etc., it may be that each 
plant contains, in some one or all of its parts, one or 
more chemical compounds peculiar to itself, so that 
there may be as many distinct chemical compounds in 
the vegetable kingdom as there are different species 
of plants. This, of course, cannot be known absolutely 
until all plants in existence have been carefully 
analysed ; but, whether the number of different 
chemical compounds in the vegetable kingdom be a 
few thousand or a few hundred thousand, we know 
that they are almost entirely made up of fourteen 
elements, and these, therefore, form the chemical 
alphabet of the vegetable kingdom, all the different 
vegetable compounds, like words from letters, being 
formed by the union of two or more of these elements. 
The fourteen elements which are regarded as being 
necessary to the perfect growth and development of 
every plant are the following : Carbon, laydrogen, 
nitrogen, oxygen, phosphorus, sulphur, chlorine, silicon, 
calcium, iron, magnesium, manganese, potassium and 
sodium. The element fluorine is of frequent occur- 
rence in very small quantities, and the following 
elements are of rare or doubtful occurrence : Alumi- 
nium, barium, bromine, cobalt, copper, iodine, lead, 
lithium, nickel, rubidium, tin, titanium and zinc, but 
their occurrence is a matter of curiosity rather than of 
practical importance, for, unlike the fourteen named 
above, they seem in no way to be necessary to plant 
life. 
AIR-DEBIVED AND SODL-PERIVED ELEMENTS. 
7. The elements that are necessary to the growth 
of plants may be divided into two quite distinct classes, 
which have important and marked differences. These 
two classes are: (1). Air- derived or organic elements. 
(2). Soil derived or inorganic elements. 
AIR-DEKIVED EL 
Carbon. 
Hydrogen. 
Oxygen. 
Nitrogen. 
SOIL-DERIVED ELEMENTS. 
Phosphorus. 
Sulphur. 
Chlorine. 
Silicon. 
Calscium. 
Ii'on. 
Potassium. 
Sodium. 
Magnesium, 
Manganese. 
8. It is usual among writers on agricultural chemis- 
try to call these classes organic and inorganic ele- 
ments, but this use of these words is extremely in- 
accurate : for any element may be either organic or 
inorganic, according as it is or is not a part or pro- 
duct of an organized body. Oxygen, as it exists in the 
air, is inorganic matter ; but when, through vital pro- 
cesses, it becomes part of an animal or plant, it is 
organic. 
9. These two classes of elements differ in three im- 
portant particulars, as follows : — 
F rst. — The elements of the first class are derived 
exclusively from the air, either, directly or indirectly ; 
while those of the second class come exclusively from 
the soil. 
Second. — Air-derived elements disappear, for the 
most part, in the form of gases, when a plant is 
burned ; while the soil-derived elements, usually the 
smaller part, are left in the form of a residue or ash, 
which further heating will not have any effect upon. 
Some carbon and oxygen and nitrogen are always 
found in the ash, while slight quantities of chlorine, 
sulphur and phosphorus are apt to be driven off by 
heating. The two classes of elements are, therefore, 
not so sharply defined in this regard as they are in 
respect to the sources from which they come. 
Third. — These two classes differ very noticeably in 
regard to the quantities in which they are present in 
plants. Thus, the air-derived elements constitute, at 
least, ninety-five per cent, of the whole vegetable 
kingdom, while the soil-derived elements occur in 
small quantities, varying from a fraction of one per 
cent, up to ten per cent., or even more in some cases. 
Because the soil-derived elements occur in so much 
smaller quantity, it does not follow that their presence 
is of less importance ; in their absence, vegetation 
would disappear. 
We will now consider each of these elements in 
order, and mention briefly some of the more im- 
portant characteristics of each ; but, before doing 
this, it is desired to explain the meaning of two or 
tliree chemical terms which we shall have occasion to 
use. 
AClD-FOHjnNG ELEMENTS AND METALS. 
10. Of the fourteen elements which are fomid in 
plants, some are spoken of as non-metallic elements 
or acid-forming elements, because, in certain com- 
binations, these elements form well-known acids. The 
other elements are known as metallic elements or 
metals. 
ACID-FOHMING ELEMENTS. SfETAI.S. 
Carbon. Calcium. 
Hydrogen. Potassium. 
Oxygen. Sodium. 
Nitrogen. Iron. 
Phosphorus. Magnesium. 
Sulphur. Manganese. 
Chlorine. 
Silicon. 
ACIDS AND SALTS. 
11. An acid is a compound containing an acid-form- 
ing element combined with hydrogen and oxygen, or, 
in some cases, with hydrogen alone. The following 
examples will serve to illustrate : — 
Nitrogen, hydrogen and oxygen form nitric acid ; 
phosphorus, hydrogen and oxygen form phosphoric 
acid; sulphur, hydrogen and oxygen form sulphuric 
acid ; chlorine and hydrogen form hydrochloric acid. 
The common name of sulphm'ic acid is oil of vitriol ; 
the common name of hydrochloric acid is muiiatic acid. 
1'2. A salt is a compound formed by putting a meta, 
in the place of the hydrogen of an acid ; that is, a 
acid differs from a salt simply in having a metal where 
the acid has hydrogen. Every acid has a salt corres- 
ponding to it. for example, as stated above, nitric 
acid consists of nitrogen, hydrogen and oxygen. Now, 
if we put the metal potassium in tlie place of hydrogen, 
we have a compound containing nitrogen, potassium 
(in place of hydrogen) and oxygen. This com- 
pound is the potassium salt of nitric acid and is called 
potassium nitrate, or, sometimes, nitrate of potash. 
Again, phosphoric acid consists of phosphorus, hydro- 
gen and oxygen ; in place of hydrogen, put one of the 
metals, as calcium, and we have a compound contain- 
ing phosphorus, calcium (in place of hydrogen) and 
oxygen, which is the calcium salt of phosphoric acid 
and is called calcium phosphate, or, sometimes, phos- 
phate of lime. Similarly, if a metal, as magnesium, is 
put in the place of the hydrogen of sulphuric acid, we 
nave the magnesium salt of sulphuric acid, or mague- 
