58 
THE CULTIVATOR. 
5. Alkalis. 
6 . - Nitrogen, occasionally developed in the form of ammonia. 
7. Acids, remaining in the insoluble, or washed away in the soluble 
The chemical examination of vegetable bodies ought of course lead 
to similar results. The examination has been conducted in three dif¬ 
ferent ways. 
L With the view of discovering the nature of the compounds, called 
vegetable principles, which exist ready formed in plants. 
2. For the purpose of discovering the chemical elements contained in 
these principles. „ , 
3. By the destructive action of heat, under which some of the ele¬ 
ments are wholly separated, and others enter into new combinations. 
In the first of these methods there have been detected s 
I. Certain peculiar acids, of which we may cite, 
(1) Acetic acid, which, mixed with water, forms common vinegar. 
(2) Citric acid, which is found in the lemon and orange. 
(3) Malic acid, which exists in the apple. 
(4) Tartaric acid, in the juice of the grape. 
(5) Oxalic acid, in the wild sorrel. 
II. Certain substances of alkaline character, found principally in me¬ 
dicinal plants, to which they give their peculiar virtues, 
III. Gum, resin, oils, sugar, starch, and two substances approaching 
to animal matter in their characters, namely, albumen and gluten; the 
former of these has a resemblance to the white of eggs, the latter to ani¬ 
mal jelly or glue. 
Many other principles are separated by the same method in differ¬ 
ent plants, but need not be enumerated by us. 
The basis of this method consists in acting upon vegetables by wa¬ 
ter, ether, or rectified spirits (alcohol,) and the principles above enu 
merated are either simply, or in the state of combination in which they 
exist in plants, soluble in at least one of the liquids we have named. 
In all cases some insoluble matter is left, and this is known by the 
frame of the woody fibre. 
When these principles are treated by the second method, oxygen, 
hydrogen, and carbon, are the uniform results, but in different propor¬ 
tions in the different cases; nitrogen is also detected in some of them, 
as, for instance, in the alkaline principles and in gluten. This method 
dJes not appear to be adequate to determine whether earth and alkalies 
are, or are not, parts of these vegetable principles. From the very re¬ 
markable fact, that some of those substances, which are very dissimilar 
to each other, yield exactly the same proportions of oxygen, hydrogen, 
and carbon, we may fairly conclude by chemical analogy, that one or 
the other, or perhaps both, contain some substances which have escap¬ 
ed the analysis. As an instance we may cite starch and sugar, whose 
characters are so dissimilar that no danger can exist of mistaking the 
one for the other; and yet their analysis by the second method gives 
identical results. 
The third method may be understood by comparing it with the pro¬ 
cess used in making charcoal. If this be so far altered that the heat 
employed shall not rise from the combustion of a part of the substance 
to be examined, but from one merely used as fuel, and if the matters 
which escape in smoke are condensed and collected, we shall have that 
employed occasionally on a large scale by operative chemists. In this 
way charcoal will be, as usual, obtained in the solid form. The con¬ 
densible products will be water, tar, turpentine, or resin; and the acid 
which gives that character to vinegar, but which in the present case is 
union with the tar and water, is called pyrolignous acid. 
If the charcoal be burnt in a current of air, all its carbon is convert 
ed, by union with the oxygen of the atmosphere, into carbonic acid, 
leaving a residue familiarly known as ashes. The ashes are made up 
partly of soluble, and partly of insoluble matter. The soluble matter 
is separated by the familiar process of making ley, and the ley, if eva¬ 
porated, leaves the solid substances so well known as potash. 
Potash is principally composed of a carbonate of potassa, but con¬ 
tains, besides silica, rendered soluble by the alkali, sulphate and muri¬ 
ate of potassa, and a peculiar acid known by the name of ulmic, which 
is a compound of carbon, hydrogen and oxygen. The insoluble part 
is made up of carbonate of lime, sulphate and sometimes phosphate of 
lime, silica. The carbonate of lime has probably in no case existed 
in the living plant, but arises from the destruction by heat of the pecu¬ 
liar acid of the plant: as, for instance, the citric, the oxalic, or the tar¬ 
taric; all of which are by fire converted into carbonic acid. 
The quantity of ashes is extremely various, as is their proportion of 
the several soluble and insoluble substances, we have mentioned. 
Thus the ashes of the stalk of Indian corn yields 12J per cent of alkali, 
while the softwoods do not furnish more than two parts in a thousand. 
The proportion of the sulphate and phosphate of lime is even more 
various. Thus, in some cases the presence of the sulphate is hardly 
perceptible, while of the ashes of clover it forms a large proportion of 
the whole weight. Phosphate of lime is found in the proportion of 
fifteen per cent, in the grain of wheat. 
Water is not only one of the principal component parts of all plants, 
but is also the sole vehicle of their nutriment. At each extremity of 
the small fibres into which the roots of plants are divided, is an open¬ 
ing through which that fluid enters ■, and it appears that, except in the 
case of a plant having lost its vigor by continued drought, it is only 
through this channel that water can enter. By a powerful action in¬ 
herent in living vegetables, water, which, with all the matter it is capa¬ 
ble of holding in solution, becomes the sap,* is raised to the highest 
parts of the plants, and forced to their most distant extremities. It 
has been ascertained that plants do not possess the power of rejecting 
even those substances which are most noxious to them; it is, therefore, 
probable that the character of the fluid admitted is the same in all the 
plants which grow upon the same soil. Whether it undergoes any 
change in the root does not appear certain, but it has recently been 
maintained that every description of plant throws off by the surface of 
its roots such matter as, if retained, would be injurious; but this opini¬ 
on does not appear to be well established. 
The sap, when carried up to the leaves, undergoes an important 
change, principally owing to the action of solar light. When exposed 
to light, the leaves of plants give out oxygen in considerable quanti¬ 
ties. This proceeds from a decomposition of the water and carbonic 
acid, the remaining elements of which two substances and a portion of 
their oxygen enter into new combinations. These combinations have 
different characters in different vegetables, but are most familiarly 
known in the shape of gum and resin. These still contain the earthy 
and saline matter carried up by the sap, and after they are formed re¬ 
turn downwards towards the roots. In their descent they deposite the 
several parts which minister to the growth of the plant—the leaves, 
the bark, and the woody fibre. They also appear to be forced with 
powerful energy into the flower and the growing fruit, and in these a 
still more important action is carried forward, by which the reproduc¬ 
tion of the species is ensured. 
The matters which the water that enters by the roots may hold in 
solution, are either derived from the atmosphere or from the soil. In 
its passage through the air it will carry with it a considerable propor¬ 
tion of carbonic acid, and all the sulphuretted hydrogen it meets with. 
It will also take up a small quantity of oxygen, and of carburetted hy¬ 
drogen, and a still less quantity of nitrogen. From the soil it will take 
all the more soluble salts, small quantities of sulphate, phosphate, and 
carbonate of lime, provided they be present, and silica. So also if the 
soil contain animal matter, or vegetables of which nitrogen forms a 
part, the ammonia generated by their decomposition will likewise be 
dissolved by the water. In like manner the carbonic acid, which has 
arisen from the decomposition of vegetable or animal matter, and has 
not yet escaped, and the soluble compounds of carbon, oxygen, and hy¬ 
drogen, which are generated by the same process, will have been taken 
up, and carried by the water into the root of the plant. It will thus ap¬ 
pear that, contrary to the opinion of M. Puvis, the atmosphere fur¬ 
nishes but little of the fixed elements of plants, with the exception of 
sulphur and carbon : and that even if the growth of plants were to de¬ 
pend wholly upon the carbon obtained in the form of carbonic acid from 
the atmosphere, their growth must be slow and feeble. It will also ap¬ 
pear, that if lime do not exist in the soil, but few plants can find nou¬ 
rishment ; and that for the ripening of the seeds of grain, phosphorus 
must be furnished also. The latter substance may be absorbed in small 
quantities from the phosphuretted hydrogen, which is occasionally pre¬ 
sent in the atmosphere; but a more certain supply ought to be sought 
in putrescent manure, and particularly in that of animal origin. 
The uses of lime in agriculture, as will appear from the foregoing re¬ 
marks and the reasoning of the essay, are as follows : 
1. When a soil contains inert animal or vegetable matter, their de¬ 
composition may be promoted, and it may be rendered fit for the food 
of plants, by the addition of caustic lime. 
2. If the soil contain acid, that may be neutralized either by caustic 
or carbonated lime, and besides, the organic matter whose decomposi¬ 
tion may have been prevented by the acid, will be permitted to putrify. 
3. Soils containing too much silica, or in other words those which are 
sandy, are made more retentive of moisture by the addition of lime or 
its carbonate. 
4. Clays, may be rendered less retentive of moisture, and more fria¬ 
ble by the same means. 
5. The gases which escape when vegetable or animal matter putrify, 
are retained in the soil by means of lime or its carbonate ; and thus a 
given quantity of manure, or the original vegetable matter of the soil, 
will retain its efficacy longer. By a recent discovery, it has also been 
ascertained that the decomposition of plants yields a peculiar acid, called 
the humic, which forms with lime a salt sparingly soluble in water. 
The generation of this salt also serves to render the nutriment con¬ 
tained in the soil more lasting. 
6. Lime and its compounds are absolutely necessary, as constituent 
parts, to the growth of many plants. The sulphate is essential to the 
*See Roget’s Bridgewater Treatise. 
