128 
THE CULTIVATOR. 
proportions of alumina and silica, of carbonate of lime and vegetable 
and animal matter, appears to be the best suited for absorbing the 
humidity of the atmosphere, of preserving it, and transmitting it the 
most regularly to the plant. 
Neither does it appear that the prevalence of any one earth in a 
soil is favorable to vegetation. Too great a proportion of alumina 
forms a soil too stiff and tenacious. Such a soil will, from this cause, 
be found to be unproductive. A soil consisting of carbonate of lime 
only, as we see in the case of chalk, is a bad soil. A soil consisting 
of alumina and carbonate of lime only, as we see in the case of clay- 
marl, is unproductive as a soil, until mixed with other substances. 
A soil consisting chiefly of silica, is often so barren as to be incapa¬ 
ble of sustaining vegetation at all. 
Some, founding on the experiments of Sir Humphrey Davy, have 
been led to the opinion, that the fertility of soils is directly indicated 
by their power of absorbing water from the atmosphere, and that 
their relative fertility may be estimated by this circumstance alone. 
Sir Humphrey Davy compared together the absorbent power of various 
soils with respect to the moisture of the atmosphere, and found it to 
be the greatest in the most fertile. Thus; 1000 parts of a celebrat¬ 
ed soil from Ormiston in East Lothian, when dried at 212®, gained 
in an hour, when exposed to air saturated with moisture at the tem¬ 
perature of 62®, 18 grains. 
1000 parts of a very fertile soil from the banks of the river Par- 
ret in Somersetshire, under the same circumstances, gained sixteen 
grains. 
1000 parts of a soil from Mersea in Essex, worth 45s. an acre, 
gained 13 grains. 
1000 parts of a fine sand from Essex, worth 28s. an acre, gained 11 
grains. 
1000 parts of a coarse sand, worth 15s. an acre, gained only 8 
grains. 
1000 parts of the soil of Bagshot-heath gained only 3 grains. 
It is an error, however, to hold that the relative fertility of soils 
may be determined by their power under the circumstances men¬ 
tioned, to absorb moisture from the atmosphere. The power of soils 
to retain moisture when absorbed, and thus to supply it in due quan¬ 
tity to the plant, is also to be taken into the account. Peat-earth 
is a very absorbent soil, but it is not a soil of great fertility. It parts 
with the moisture absorbed with too great facility. Besides, to infer 
that the fertility of soils depend upon their powers either to absorb 
or to retain moisture, were to reason as if these were the only con¬ 
ditions of fertility in soils, which does not appear to be the case ; and 
other experiments accordingly do not bear out the conclusion that 
the fertility of soils depends upon these properties. But this may be 
inferred, that all productive soils have a considerable power of ab¬ 
sorbing moisture and retaining it when so absorbed, and that the 
property does not depend on the prevalence of any one substance, 
but on a mixture of several substances. 
It has been found, also, we have seen, that the fertility of soils, 
however produced, is not dependant on the prevalence of any one 
mineral in the soil, but on a mixture or combination of several. But 
what the precise proportion of these is which is the most favorable 
to fertility, has not yet been determined. 
Without detailing any of the numerous experiments of chemical 
analysis that have been made, with the design of ascertaining this 
and other points relating to the properties of soils, the following con¬ 
clusions may be given as apparently deducible from the investiga¬ 
tions that have taken place : 
1. Soils in which the largest quantity of silica and alumina exists 
in the state of impalpable division, are, cceteris paribus , the most fer¬ 
tile. 
2. Soils in which the quantity of silicious sand is largo are com¬ 
paratively infertile: while soils in which the sand is fine and only 
partially silicious, are comparatively fertile. 
3. Oxide of iron exists in all soils, but does not influence their fer¬ 
tility in proportion to its larger or smaller quantity. 
4. An excess of the acid combinations of the oxide of iron, and 
certain other saline bodies, is hurtful to vegetation. 
5. Carbonate of lime exists in the best soils, and generally, though 
not always, in larger quantity in the better than in the inferior soils. 
6. Certain earths possess the power of combining chemically with 
animal and vegetable matter, and of retaining it for a longer or short¬ 
er time. Thus, alumina and lime form certain compounds of great¬ 
er or less insolubility with animal and vegetable matters, while silica 
will not enter intotiie same combinations; and hence it is that alu¬ 
minous and calcareous soils retain for a longer time the manures ap¬ 
plied to them than silicious soils. 
7. When water is in excess in the soil, and when vegetable mat¬ 
ter is present, acid is formed which is injurious to the productive 
powers of the soil. In the first stages the acid appears to be the 
acetic; in the latter stages, when the matter of the vegetable is be¬ 
ing converted into peat, the acid appears to be the gallic, and the 
tannin principle is formed. 
8. Soils, besides absorbing moisture from the air, appear to absorb 
carbon and other matters nutrimental to plants. 
These are the principal results to which the chemistry of agricul¬ 
ture has conducted us with respect to soils. This branch of sci¬ 
ence, however, may be said to be as yet imperfect, and a large field 
of useful investigation still remains for the philosophical inquirer. 
Although it may be said that much has not been done with relation 
to the really useful, which observation and practice had not before 
shown, yet we have at least escaped from the errors of former opi¬ 
nions, and so far the path of further inquiry is more open to us. 
Amongst other results to which this species of investigation has 
conducted us, we have seen—that the practice known to agricultu¬ 
rists of mixing together different kinds of earths, admit of explana¬ 
tion on principles founded on our knowledge of the composition of 
soils ; that the beneficial action of manures depends upon a proper 
constitution and texture of the mineral portion of the soil, and that 
hence to derive the full benefit of manures, the province of the culti¬ 
vator is to improve the texture and constitution of the soil: that the 
comminution of the component parts of the soil is beneficial, as ren¬ 
dering the whole more pervious to the air, and the vapor, and other 
matters, with which the atmosphere is charged : and further, we 
have been enabled to render our common nomenclature of soils more 
precise, by distinguishing them by the terms Silicious, Aluminous, 
Calcareous, Magnesian and Ferruginous, as silica, alumia, lime, 
magnesia and oxide of iron, prevail in their composition. 
We might now proceed to consider the relation existing between 
the soils of a country, and its geological condition. This is a sub¬ 
ject interesting to the scientific agriculturist. But however curious 
the investigation might prove, it is not necessary for that practical 
illustration of the subject of soils, which consists with the design of 
this work. Besides, to characterize the quality of soils, as affected 
by the geological nature of the country or district, is to view the 
subject in a somewhat more extended manner than is consistent with 
the common purposes of the farmer. Although it is found that a re¬ 
lation may be generally traced between the nature of the rocks of a 
country or district, and its fertility—as, in the British Islands, between 
the new red sandstone and the finest districts of the country; be¬ 
tween the coal formation, under certain circumstances, and a ferru¬ 
ginous and somewhat ungrateful soil; between the magnesian lime¬ 
stone and a tract of comparative infertility ; between the lias forma¬ 
tion and one of comparative productiveness, and so on—yet many 
degrees of quality may exist in the soils of the same series of rocks, 
and in the same country; and even all the contrast between great 
fertility and great barrenness may be found within the limits of a 
single field. We must, therefore, narrow our views when we ex¬ 
amine the soils which we have occasion to cultivate, and regard, not 
their properties with relation to an entire district, but their minuter 
shades of fertility and character. 
We have thus considered their properties as determined by their 
external characters, and in part by their chemical composition. We 
may now consider their characters as determined by their vegetable 
productions. 
Miscellaneous. 
EXPERIMENTS IN RAISING POTATOES. 
BY JOHN ROBERTSON, OF CARLOW, IRELAND. 
Experiment 1.—Mr. Robertson marked off, on an average portion 
of his potato ground, four drills, twenty yards each in length ; in two 
of these he planted potato seed of the red-nosed kidney species, and 
in the remaining two of the apple kind. These lie earthed up in the 
usual way : in these earthed drills the product was six pounds (about 
10 per cent) less than in four corresponding ones unearthed. In all 
those drills, (which were 30 inches apart,) the sets were placed from 
ten to twelve inches asunder. The treatment of the unearthed drills 
may be thus stated: They were dug at bottom twelve inches deep, 
and left half full of the crumbling clods; on these the potatoe were 
laid, and then covered about three inches with dung, over which an 
