THE CULTIVATOR. 
155 
The action of lime upon soil differs entirely according to 
the state in which it is used, namely, in the form of true lime, 
hot lime, or in the state of mild lime, as it is termed, in assum¬ 
ing which condition it has undergone some most important 
chemical changes which we shall mention presently. 
The chemical properties of lime, and its chemical action 
upon organic matter, must, in the first instance, occupy our 
attention, in order that the subsequent remarks upon its use 
as a manure may be clear and intelligible. Lime is ranked 
by chemists among the alkaline earths, by which term is meant 
those earthy substances which exhibit characters similar in 
many respects to the true caustic alkalies, potass, soda, fife. 
it is always prepared by heating its native carbonate or lime¬ 
stone, to a temperature sufficiently high to drive off all the 
carbonic acid and water which it contains; so that were lime¬ 
stone composed of nothing else but carbonate of lime and 
water, pure lime alone would be left after burning; this, 
however, is never the case, as other substances, especially 
alumina, silica, iron, and often magnesia, occur mixed with 
the lime, but in good specimens these should be in very small 
quantities, as of course, I need hardly say that their presence 
diminishes the value of the specimen in direct proportion to 
their quantity. On this account, the proportion of lime con¬ 
tained in any new specimen of limestone should be accurately 
determined before applying it to agricultural purposes, more 
especially if there should be any reason for suspecting the 
presence of magnesia which we have so repeatedly said is in¬ 
jurious to vegetation, particularly in its caustic state. On 
this account we shall here give a few directions for the ex¬ 
amination of limestone, which we trust will not be consider¬ 
ed out of place. Let us suppose that the experimenter is not 
desirous of ascertaining the exact constitution of the limestone 
which he is about to examine, but merely wishes to discover 
whether it contains any considerable quantity of magnesia, 
alumina, or iron. 
1. Let him take a small quantity of the sample to be ana¬ 
lyzed, say 100 grains, and dissolve it in one ounce of strong 
muriatic acid (spirit of salt) mixed previously with about 2 
ounces of pure water; when the effervesence (owing to the 
escape of carbonic acid) has entirely ceased, if any thing is 
left undissolved it must be separated from the solution, by fil¬ 
tration through white blotting paper, and the insoluble mat¬ 
ter when dried and weighed may be noted down as silica. 
2. The operator must next add to the filtered fluid succes¬ 
sive portions of strong ammonia (hartshorn) until the liquid 
smells of this substance; any thing which is thrown down 
during this operation must be likewise separated by filtration; 
this will consist of alumina and iron, the proportion of the 
latter being judged by the darkness of the colour [pure alu¬ 
mina being white.) 
3. The next step is to add to the fluid a solution of oxalate 
of ammonia (this should be prepared by a druggist) as long as 
any precipitate appears; this is the lime in combination with 
the oxalic acid. 
4. Lastly, having again filtered the solution, add a small 
quantity of carbonate of soda (common soda) dissolved in wa¬ 
ter; if the former parts of the process have been performed 
carefully, no precipitate whatever will now appear, unless 
magnesia is present, so that the quantity of this substance 
may be judged by the proportion of this precipitate. 
Difficult as this process may appear to those who have ne¬ 
ver performed any chemical analysis, still a very little prac¬ 
tice will make it quite familiar, and it is the only method by 
which the presence of magnesia can be detected with unva¬ 
rying certainty; at least without making use of chemical 
tests, which cannot be easily purchased, and are very trou¬ 
blesome to prepare. Should any one wish to render himself 
expert at the above operation, I should recommend his tak¬ 
ing some specimens of limestone, and repeating the process 
several times, until he arrives at the same results by each 
experiment. If the quantity of lime is wished, the precipi¬ 
tate of No. 3 must be carefully collected, dried, and weighed; 
and then, every 100 grains will denote 34 grains of pure 
lime, or 61 grains of carbonate of lime in the original speci¬ 
men. 
Whenever lime, in its pure or hot state, is exposed to the 
air, it has a very great tendency to return to the original form 
of carbonate; in undergoing which change, it first absorbs a 
large quantity of water; and then assumes the form of slaked 
lime, or, according to chemical nomenclature, has become a 
hydrate; this hydrate, in its turn, rapidly absorbs carbonic 
acid from the air, and thus, in no long period, the burnt lime 
returns to its original condition, with the only difference, that 
whereas it was formerly in large stony masses, it is now in the 
state of a fine powder. When the lime is completely slaked, 
and partially carbonated, it forms the substance termed mild 
lime, by farmers. 
Of these three conditions of lime, namely, the hot, the mild, 
and the true carbonate, the first is possessed of by far the most 
energetic powers. The true carbonate of lime, in fact, differs 
completely in its action from the others. We must, therefore, 
of necessity, treat of each separately. 
Hot Lime. —When any organic matter is mixed with hot 
lime, it undergoes putrefaction with much greater rapidity 
than when left to itself. The exact cause of this is not well 
known; but the immediate changes which the various sub¬ 
stances undergo, especially in the case of vegetable matter, 
have been pretty accurately examined. Thus, for example, 
it has been proved^rst, that woody fibre, gum, sugar, and 
many other vegetable matters, are converted into humic acid, 
with more or less rapidity, when kept in contact with hot 
lime, or any other chemical substance which possesses strong 
alkaline properties. Secondly, that this humic acid, when 
formed, unites with the lime, and generates a compound 
which is not very soluble in water, but is easily diffused 
through it. And, lastly, it has been proved, that a very lit¬ 
tle lime is required to produce this compound, with a large 
quantity of humic acid. For example, 28 grains of pure lime 
are capable of combining with no less than 318i grains of 
this acid; so that the lime in this compound amounts to little 
more than eight per cent. 
To apply these facts, therefore, we may remark, that there 
is very little doubt, that changes similar to those above men¬ 
tioned take place, when hot lime is applied to soil; or, still 
more so in the case of lime composts. At the same time, it 
is exceedingly probable, that during the production of humat.e 
of lime* * (the compound of lime and humic acid above me n- 
* I have continued to denominate this acid, humic acid, 
although I find that, latterly, especially in chemical works, 
tioned,) other compounds are formed, many of which are very 
possibly soluble in water; at least if we may judge by the 
appearance presented by vegetable matter, after it has been 
long exposed to the action of this or any other alkaline mat¬ 
ter. From these remarks it would appear, that the most im¬ 
portant object to be gained by the application of hot lime, is 
the decomposition of woodyfibre, and the consequent formation 
of humate of lime, and various soluble matters. 
Mild lime does not act by any means so powerfully as the 
preceding compound; m fact, it appears to have no eiitect 
whatever upon woody fibre. On the other hand, however, it 
is capable of uniting with the humic acid existing in the soil, 
precisely in the same manner as hot lime; on which account, 
Sir Humphrey Davy remarks, that mild lime is useful in pre¬ 
venting the too rapid decomposition of substances already 
dissolved; the truth of which is evident, when we call to mind 
the well established fact, namely, that organic substances, 
which of themselves are extremely liable to decomposition, 
may be rendered much more permanent, nay, often perfectly 
so, by entering into chemical combination with any inorganic 
substance. Pure carbonate of lime will be treated of under 
the head of chalk. 
So much for the pure chemistry of this most important ma¬ 
nure. We must, however, now proceed to what the majority 
of our readers will consider as by far the most interesting part 
of the subject, namely, the practical deductions to be drawn 
from the above remarks; or, in other words, the manner in 
which practice is to be guided by the principles above laid 
down. 
j First. —It is perfectly clear, that hot lime will be useful in 
all cases where there is an excess of undecomposed vegetable 
fibre, as in peat-soils, moors, heaths, &c. in fact, in ail places 
where the natural growth has not been interfered with for a 
great number of years; from which it follows, that hot lime 
will be a peculiarly useful application to old grass, which has 
lost heart from age, particularly if it is, at the same time, 
broken up for tillage. 
Secondly. —Sir Humphrey Davy has proved, that hot lime, 
whether solid or dissolved, is injurious to growing plants.— 
For example, he states, that he has frequently killed grass by 
watering it with lime water. From this fact, therefore, it 
follows, that hot lime must be an extremely useful application, 
when it is desired to free land of its spontaneous growth; as 
for instance, in places overgrown with weeds. 
Thirdly. —Hot lime is extremely useful in purifying (if we 
may be allowed the expression) the original herbage of moors, 
and other uncultivated grounds. The mode in which this is 
effected being somewhat interesting, we shall here say a few 
words upon the subject. It is generally allowed, that the 
finer grasses, &c. require richer food than those which are 
less valuable; and also, that the same remark holds good, 
the lower we descend in the scale of vegetables: namely, 
that the lower the plant is, the more easily it is nourished by 
the contents of the atmosphere; and hence the less dependent 
it is upon the soil for its subsistence; the consequence of 
which is, that when, in the lapse of time, the soil of any spot 
becomes more and more exhausted, the most valuable and im¬ 
portant grasses gradually die away, from the want of sufficient 
nourishment, and give place to those diminutive species, 
which so frequently constitute the herbage of the almost bar¬ 
ren moors; these again, if moisture be present, give place, in 
their turn, to various mosses, &c. so that at last, unless the 
improving hand of man steps in to avert the doom, the spot 
will return to a state unfit for the support of any living plant, 
with the exception of those which derive most, if not all, their 
nourishment from the surrounding air. Should it be other¬ 
wise, how different the result! For instance, should hot lime 
be applied, from the looseness of their texture, this destroyer 
first attacks the mosses and all other useless plants, and thus 
converts them into useful manure, which, by being washed 
into the soil by genial showers, revives the seeds of those 
plants which grew there ages previously, and, in a compara¬ 
tively short time, the lately unprofitable waste glows with the 
return of its pristine verdure. How beautifully many of my 
readers must have seen this exemplified, in the crops of white 
clover which so frequently appear, almost like magic, after 
the liming of some barren moor! 
Fourthly.—Mild lime is a most useful application in all 
cases, where any of the above circumstances occur in culti¬ 
vated land. For instance, if the lime is comparatively fresh, 
it is much safer to employ it in the mild form, when we de¬ 
sire to destroy weeds or other injurious plants, growing upon 
richly manured lands, which, from carelessness or other such 
cause, have been allowed to become foul; for, were the lime, 
in this instance, applied in its caustic state, although it would 
unquestionably kill the weeds, still, their destruction would 
be accompanied with a great unnecessary loss of manure. 
Fifthly. —It sometimes occurs, more particularly in garden 
ground, that the crops become rank, from the existence of a 
superabundance of soluble manure, the evil effects of which 
can almost always be counteracted by a dressing of mild lime, 
which, by combining with the humic acid, renders a large 
quantity of the organic matter much less prone to decompo¬ 
sition, and likewise, at the same time, less soluble; humate of 
lime, as before remarked, being by no means very soluble in 
water. It may very probably be asked here, how can it be 
advantageous to apply lime in any case to soil, since it tends 
to render soluble matters insoluble, when it has all along been 
stated that the very reverse is the proper mode of preparing 
the food for plants ? An answer to this question must, there¬ 
fore, of course, be requisite. It must be observed, in the first 
place, that we have already stated that lime is useful chiefly 
in those cases where the organic matter is insoluble, because 
it causes the formation of humate of lime and different soluble 
matters; all we have to account for therefore is, how humate 
of lime comes to be a useful manure ? It may be remembered 
that I stated in No. 2, of this series,* that humic acid was of 
itself “ quite insoluble in water:” from the result, however, 
of some experiments published since that number was writ¬ 
ten, it appears that this statement is not strictly correct, for 
humic acid is soluble in water (more especially when newly 
formed) except under particular circumstances, so that it is 
extremely probable that the humic acid derived from the slow 
decomposition of humate of lime, will, at the moment of its 
the term ulmic acid has been substituted for it. 1 trust, how¬ 
ever, that this will cause no confusion, as the difference is in 
the name only. 
* No. XLII. p. 241. 
liberation, be capable of dissolving in water, and thus o f 
course become a useful manure. We shall now conclude our 
remarks upon lime with a few important cautions to be at¬ 
tended to in its application. 
Mr. Arthur Young remarks, that the best directions for 
applying lime are those given by Mr. Craike of Arbigland, 
who advises, that the whole quantity of lime that the farmer 
intends to apply to any field of moderate size, should be cart¬ 
ed out, and laid together in a heap, at some spot where wa¬ 
ter can be obtained with the greatest facility. The whole is 
next to be thoroughly slaked; and immediately after it has 
cooled, which will take place in a day or two, the lime is to 
be recarted and spread over the surface of the land as equally 
as possible. Mr. Craike further remarks, that the more com 
moil method of laying down the lime in small heaps all over 
the field, and allowing it to slake by rain, is very erroneous; 
for in this instance it is very liable to get too much rain, which, 
in place of merely slaking it, and thus reducing it to a fine 
powder, converts it into “ running mortar,” in which con¬ 
dition “ it will neither spread easily, nor mix with the soil.” 
On the same principle Mr. Wight observes, that both the 
lime and the soil should be perfectly dry at the time of ap¬ 
plication. The truth of these remarks could have been pre¬ 
dicted by scientific examination alone, and it is at all times 
pleasing to discover that the results of successful practice di¬ 
rectly correspond with the indications of true theory. For 
example, there are many scientific objections to be made to 
the plan of laying the lime in small heaps all over the field 
in order to be slaked by the rain, in addition to the evident 
one, mentioned by Mr. Craike, namely, the formation of 
“running mortar.” These are, 1st, that it exposes a far 
greater surface for the absorption of carbonic acid, which, as 
is evident from the remarks already made upon this subject, 
diminishes materially the effect of the lime. 2d, It must ne¬ 
cessarily be exposed for a much greater length of time, and 
consequently will most probably be entirely converted into 
carbonate of lime; or it must be spread upon the land during 
wet weather, which will of course render it far more difficult 
to incorporate properly with the soil. And lastly, its being 
slaked by rain-water is directly injurious, as it has been prov¬ 
ed that there is a greater quantity of carbonic acid present in 
the air, during dull than in bright weather, which gas will of 
course be absorbed by the rain, and thus carried to the lime, 
so as to increase still more the chances of its becoming carbo¬ 
nated. On the other hand, however, it is evident that all 
these objections maybe obviated by adopting the simple, and 
if we look to the result, the much more economical method 
proposed by Mr. Craike. 
As to the period at which the lime should be applied, this 
must depend so much upon peculiar circumstances affecting 
each farmer differently, as convenience, leisure, &c. that it 
is impossible to fix the time so as to suit all persons. When, 
however, a choice can be made, summer is by far the best 
season according to Mr. Young, the reason of which is obvi¬ 
ously because it is the driest period of the year, and likewise, 
when hot lime is used to destroy weeds, they are generally 
in their greatest vigor at that time, and consequently are ca¬ 
pable of being destroyed more effectually. 
The quantity of lime to be used is likewise a subject of con¬ 
siderable importance, but nevertheless is one which is apt to 
be far too much neglected; upon this subject Mr. A. Y"oung 
is most explicit. “ In common cases,” says he, “ the quan¬ 
tity should be guided by a chemical analysis of the soil;” and, 
beyond doubt, this is the only sure way of applying it with 
success. What, for instance, can be more absurd, than for 
a farmer to go on applying lime to his land, time after time, 
when perhaps his soil is already loaded with calcareous mat¬ 
ter ? It is a well established fact, that an excess of any of 
the earthy ingredients of soil exerts a most important influ¬ 
ence over the plants which grow there; this is remarkably 
the ease with the natural productions of all soils. To such 
an extent, in fact, does this hold true, that a good botanist 
will tell with great accuracy the chemical nature of the soil, 
by the plants which he finds growing upon il. If this, there¬ 
fore, takes place naturally, where seeds of all kinds must be 
be constantly deposited on every species of soil; if, I repeat, 
nature thus arranges the plants according to the constitution 
of the soil, shall we deny that they have any effect upon cul¬ 
tivated plants ? Shall we presume to say that we can grow 
all kinds of plants equally upon every variety of soil? most 
assuredly not. How, then, can that farmer expect to be suc¬ 
cessful, who, by constantly adding lime to soil already calca 
reous, at length increases this substance to such a degree that it 
is unfit for the support of any plants, except those which na¬ 
turally prefer a soil of this description? That the above 
statement is not a mere theoretical objection, is most distinctly 
proved by many facts. Who, for example, does not know 
that wheat is an unprofitable crop upon light soils ? Or, 
again, who would attempt to cultivate turnips upon strong 
clay ? Chemical analysis, likewise, of the plants themselves, 
prove most distinctly the influence which the earthy constitu¬ 
ents of soil exert over the saline composition of the ashes of 
these plants. ThusM. Saussure found, that 100 parts of the 
ashes of common fir contained 43 parts of carbonate of lime 
when grown on a limestone hill, whereas the same quantity 
contained only 29 parts when grown on granite; and again, 
the ashes of the leaves of the Rhododendron ferrug'meum 
grown upon limestone contained 43 & per cent of chalk, where¬ 
as it yielded 16| per cent only of that substance when culti¬ 
vated upon a granite soil. There can be no doubt, moreover, 
that the proportion of the different constituents of the ashes 
of plants have the greatest influence upon the vigor and pro¬ 
ductiveness of the plant itself, and I have no hesitation in 
saying that the culture of plants (more especially the garden 
culture of exotics) will never be brought to any thing like 
perfection until they have each and all been submitted to che 
mical examination; the proportion of all their saline constitu¬ 
ents accurately determined; and the nature of the soil for 
each chosen upon these grounds. I leave it to those inte¬ 
rested in such matters to decide, whether it would not be 
worth their while to take the requisite steps for the accom¬ 
plishment of such an undertaking. 
On the other hand, however, a very large quantity of cal¬ 
careous matter may naturally exist in soil, without rendering 
it unfit for the purposes of cultivation; for instance, it is 
stated by Mr. Cuthbert Johnson, in the “British Farmers’ 
Magazine” for April 1837, that “ the richest soils, on the 
banks of the Parnel, in Somersetshire, contain more than 
seventy per cent of chalk 1” But we are all well aw r are that 
there are many peculiarities in the cropping of calcareous 
