DEceMBER 1,1891.] Tf?f. TROF5CAL AGRiCULtURIST. 
423 
sium sulphate familiar to us as Epsom salt. If in hydro- 
chloric (muriatic) acid, we put some metal, as sodium, in 
place of the hydrogen, we have a compound consisting 
of sodium and chlorine, which is the sodium salt of 
hydrochloric acid and is called sodium chloride, 
sometimes muriate of soda, familiar tons as common 
salt. 
The word " salt," as used in chemistry, applies to a 
great number of compounds, and many of the sub- 
stances we have to deal with in speaking of fertilizers 
are chemical salts, that is, substances formed by put- 
ting some metal in place of the hydrogen of some 
acid. 
CAHBON. 
13. Importance of Cabbon. — The element, carbon, 
may be called the central element of all animal and 
vegetable substances ; for there is not a living thing, 
from the smallest cell to the giant tree, which does 
not contain carbon as a necessary constituent. That 
all vegetable and animal substances contain carbon 
can easily be shown by simply heating them sufficiently, 
and thus causing them io blacken or char. When, 
for example, wood is heated, the different elements of 
which it is composed, are driven off in one form or 
another, but the carbon is the last to go, and remains 
behind as a black substance or charcoal, unless heated 
higher, when it disappears or burns up. 
14. Occurrence of Carbon in Nature. — Carbon 
usually occurs in nature united into compounds with 
other elements. Thus, most products of plant life 
contain carbon combined with the elements hydrogen 
and oxygen ; such are starch, sugar and cellulose or 
woody fibre. Carbon, combined with oxygen, occurs 
in the air in the form of carbon dioxide, commonly 
called carbonic acid gas. Carbon, when combined 
with oxygen and some element such as calcium, occurs 
in the form of carbonates ; for example, marble, lime- 
stone and chalk are chemically known as calcium 
carbonate or carbonate of lime. 
Carbon by itself or in the free condition, that is, not 
united with any other elements, is familiar to us in 
several different forms ; the most common of these 
forms are (1) diamonds ; (2) graphite, which is used in 
the manufacture of lead pencils ; (3) ordinary wood 
charcoal ; (4) lamp-black ; (5) . animal charcoal ; (6) 
mineral coal. Excepting diamonds these forms of 
carbon are more or less impure, containing some 
other things mixed with the carbon. 
15. It is pertinent to make here the inquiry, "What 
is the relation of carbon to fertilizers ? " Before we 
can answer this question satisfactorily, we must know 
what is meant by a fertilizer and what must be re- 
garded as necessary constituents of a fertilizer. We 
will, therefore, turn aside from our consideration of 
the element carbon and take the opportunity, at this 
stage, to give some definitions of general and special 
terms which we shall have occasion to use more or 
less frequently. 
definitions. 
_ 16. Fertilizer. — As ordinarily spoken of, a ferti- 
lizer may be defined as any substance which, by its 
addition to the soil, is intended to produce a better 
growth of plants. 
The materials which come under the head of ferti- 
lizers are numerous in kind, and different laoth inform 
and in the manner in which they act. 
17- The following tabulated classification, while not 
strictly accurate in every respect, will serve to give a 
good general idea of the number and relations of the 
terms used in speaking of fertilizers :— 
'Stable manure. 
Refuse vegetable 
matter. 
1. Natural -{ Green Crops for 
plowing under. 
Cotton Seed. 
t,Muck, marls, etc. 
{a. complete or 
genera], 
b. incomptete 
or special. 
[ i'ropared. 
Indirect f Lime. 
(I. Direct-^ 
ai I 
M 
d 1 
i Gypsum, 
s ■ 
, SiUt, etc. 
These terms are, in general, loosely and indiscrimi- 
nately used, as their meaning is often misunderstood ; 
and so an attempt will be made here to define them 
in accordance with the best usage of the terms. 
18. A direct fertilizer is one that contains elements 
of plant food which are available at once, that is, 
which can be taken up and used immediatly by plants. 
19. The term available is applied to plant food 
which is soluble, that is, in such a condition that 
the roots of the plant can take it up readily in 
solution. 
20. Plant food is unavailable, when it is in an 
insoluble from, so that the roots of the plant fail 
to take up any part of it. A large proportion of 
plant food present in the soil is unavailable, but, 
by the action of air, water, carbonic acid, etc., it 
is gradually changed to soluble or available 
forms, which the plant can take up and use. 
As will be noticed later, phosphoric acid in the 
form of insoluble calcium phosphate, or phosphate 
of lime, is unavailable as plant food, but when con- 
verted into a super-phosphate, or soluble calcium 
phosphate, it becomes available. Unavailable plant 
food is potential food or food in reserve. 
21. An indirect fertilizer is one which does not 
furnish to the soil any needed plant food and which 
may not be a plant food at all, but which is 
characterized by the way in which it acts on the matter 
already in the soil, changing more or less of it from 
unavailable plant food to an available form. For 
example, lime, gypsum, salt, etc., are indirect fertili- 
zers, so far as they have any fertilizing action. 
Later, some attention will be given to the action of 
some of the most familiar indirect fertilizers. 
22. Natural fertilizers include the solid and liquid 
excrement of animals, all kinds of vegetable refuse, 
green crops for plowing under, cotton seed, mucks, 
marls, etc, 
23. Artificial fertilizers are also known by such 
names as commercial fertilizers, chemical fertilizers, 
prepared fertilizers, etc., and are artificial preparations 
or mixtures of fertilizing materials sold under trade 
names. The fertilizing materials used in making 
these mixtures include the substances found in 
natural deposits and by-products of numerous in- 
dustries, which are obtainable by farmers only 
through the channels of trade. Some substances 
which might be classed as natural fertilizers, such 
as cotton-seed meal and tobacco stems, are also 
included among the materials of artificial fertilizers. 
24. Complete fertilizers, known also as genera^ 
fertilizers, are those which contain nitrogen, phos" 
phoric acid and potash. 
25. Incomplete fertilizers, also called special fertili- 
zers, are those which contain only one or two of 
the three constituents, nitrogen, phosphoric acid and 
potash. 
26. There is a common practice among farmers 
and dealers, of calling all commercial fertilizers "phos- 
phates," regardless of whether they contain any 
phosphates at all or not. The practice is clearly 
objectionable, because a phosphate is not the only 
fertilizing constituent present in commercial fertili- 
zers — in some cases it may be entirely absent. The 
term "super-phosphates" applies truthfully to many 
commercial fertilizers, but even these cannot be 
correctly spoken of as simply "phosphates." 
Haying considered such definitions as we may have 
occasion to use more or less frequently, we can now 
rotm-u to 
THE relations OF CARBON TO FERTILIZERS. 
27. We know that carbon must be an important 
element in plant food, since it forms nearly one- 
half of the solid proportions of plants. Notwithstand- 
ing the fact that carbon forms so large a portion of 
plants, it has no importance as an active food consti- 
tuent of direct fertilizers. This statement may appear 
strange and the question may be asked, "Why is 
not carbon to be regarded as an essential constituent 
of direct fertilizers ? " The answer is that the carbon 
of plants comes from the carbon dioxide (carbonic 
acid gas) of the air, and tlie air furnishes an in- 
exhaustible aud available supply of this substance. 
