THE LIBRARY
OF
THE UNIVERSITY OF CALIFORNIA
LOS ANGELES
THE
PRINCIPLES
O F
AND
VEGETATION.
By FRANCIS HOME, M. D.
Feljow of the Royal College of Phyficians in Edinburgh. The THIRD E D I T I O N, with Additions.
LONDON:
Printed for A. MILLAR in the Strand,
And A. KINCAID and J. BELL, at Edinburgh.
MDCCLXIL
T A
T H E f/75/b
DESIGN."
TH E Edinburgh fociety, eftablifhed in the year 1755, for the improvement of arts and manufactures, named, amongft other articles, the following :
For the beft differ tation on vegetation and the principles of agriculture, a gold medal.
IN order to promote fo ufeful an infti- tution, the following papers were compofed, and delivered in to the fociety, according to the rules laid down. The judges named for that article, determined, on a competi- tion, in their favour. Some few additions have been made to them fince they were given in to the fociety.
IN fo neceflary an art, where the terms
are inaccurate, confufed, and differ fo much
in different counties, to fix thefe terms,
A 2 and
- '"000835
[iv]
and afcertain their meaning; where there is nothing fyftematic, to lay down a regular planj where the different parts are gene- rally looked on as complete, to mark the deficiencies, and mow that there is much wanted 5 where the means of improvement are unknown or neglected, to point out the only road that can lead with certainty to it 5 where there are few experiments to build on, to relate fome, and on thefe to lay a foundation for more; where the reafonings are, in general, fo very unphi- lofophical, to fettle fome fund for difcourfe and argument; where the proper helps have not been called in, to make ufe of thefe, and introduce a new fcience to the affiftance of this art ; in fhort, where there is but little afcertained, to fix fome general principles on which the artift may depend : this is the defign of the following papers. That no more has been done, will be moft readily excufed by thofe who are beft acquainted with the difficulty of the un- dertaking.
A
A PLAN of the whole. PART I.
SECT. I.
Caufes of the Jkia progrefs of agriculture j connection of chymiflry 'with it 5 and divi- fan of the fubjecJ.
SECT. II.
Of different foils.
SECT. III.
Of the rich black foiL
SECT. IV.
Of the clay foil.
SECT. V.
Of the fandy foil.
SECT. VI.
Of the chalky foil.
SECT. VII.
Of till.
SECT.
f vi J
SECT. VIII.
Of the mojfy foil.
SECT. I.
ffle natural methods of providing vegetable food.
SECT. II.
Of manures, or the artificial methods of pro- viding vegetable food.
SECT. III.
Of marl.
SECT. IV.
Of unburnt calcaricus bodies , and quick-lime.
SECT. V.
Of vegetables in an entire and in a corrupted Jlate, and of dunghills.
SECT. VI.
Of manures which arife from burning ve- getables.
SECT.
SECT. VII.
Of animal manures.
PART III.
SECT. I.
effects of different fubjtances with regard to vegetation.
SECT. II.
Of the food of vegetables.
PART IV.
SECT. I. Of opening and pufoerifing the foil.
SECT. II.
Efe&s of the atmofphere*
SECT. III.
Change offpecies.
SECT IV.
Of ploughing.
SECT.
[ viil ]
SECT. V.
Of compojls.
SECT. VI.
Of vegetation.
PART v,
SECT. I.
Of weeds.
.SECT. II.
Of a wet foil. SECT. III.
. Of rains.
SECT. IV.
Of faulty feeds.
SECT. v.
Difeafes of plants. SECT. VI.
Plan for the further improvement of agri- culture.
THE
THE
PRINCIPLES
O F
Agriculture and Vegetation, PART I.
SECTION I.
Caufes of the Jlow progrefs of agriculture ; connexion of chymiftry with it-, and divi* fan of the fubjett.
AGRICULTURE, though the moft necefTary, has been, per- haps, the moft neglected of all the arts. Every other art has undergone confiderable improvements in this and the laft century; but we cannot affirm the fame of agriculture. It feems to be little better underftood in 'Europe at prefent, B than
2 the Principles- of Part X.
than amongft the anrients; and I believe Virgil and Columella may ftill be reckoned the bell authors on that fubject. Does this proceed from the earth lofmg, like a mo- ther, her fertility, becaufe of her age ? as Ibrae of the antients alledged : or does it arife from an impoffibility of reducing the culture of the ground to a regular art, as the effects of that culture depend more on chance than fettled principles ? Daily experience mows, that none of thefe can be the cafe:, for the earth, though ex- haufted, attains again, under proper ma- nagement, a great degree of fertility ; and the regularity with which affairs are con- ducted, fhows,, that it is in fome meafure- akeady reduced to an art
THE flow progrefs of hufbandry may be accounted for from more obvious rea- fons. This art is, in general^ carried on by thofe whole minds have never been im- proved by fcience, taught to make obfer- vatious, or draw conclufions, in order to
attain
Seel. I. Agriculture and Vegetation. J
attain the truth ; or by thofe who, although Nature has been very bountiful, cannot carry their fchemes into execution, from the narrownefs of their fortunes. The former can never know more than what they have learned from their fathers; the latter dare rifk nothing, as their daily bread depends on the certainty of fuccefs. What can be expected from that clafs ?
LET us fuppofe the fortune eafy, and the judgment improved, the difficulty of the art itfelf is fufficient to retard its pro- grefs. How delicate the circumftances that muft attend each experiment! What a number of different obfervations on heat and cold, dry and wet, difference of foils, grains, feafons, &c. muft be exactly made, before one can be certain of the general fuccefs of an experiment ! What a dif- agreement from a fmall difference in one of thefe circumftances ! How feldom can thefe experiments be repeated, which take a whole year before they can be brought to B 2 a
4 Tfo Principles of Part I.
a conclufion ! how unequal for fuch a talk are the few years of judgment and activity we enjoy ! How liable are obfervations to die with the obferver when not made public ! and how averfe is human pride to do it, unlefs it could erect a fyitem ! Agriculture, feemingly fo eafy, appears, from the fcarcity of good authors, to be the mofl difficult of all arts.
BUT thefe are not the only obftacles that hufbandry has met with. It has yet had a greater to ftruggle with. It does not, like moft arts, lead to an account of itfelf; or depend on principles which its practice can teach. Something beyond this art is necefiary to the knowledge of the art itfelf. The principles of all external arts mud be deduced from mechanics or chymiftry, or both together. Agriculture is in the lafl clafs j and though it depends very much on the powers of machinery, yet I'll venture to affirm, that it has a greater dependence on chymiftry. Without a knowledge in
the
Sect. I. Agriculture and Vegetation. 'r
the latter fcience, its principles can never be fettled. As this fcience is but of late invention, and has not yet been cultivated with that regard to utility, and the im- provement of trades and manufactures, as it ought and might, agriculture is hardly feniible of its dependence on it. The de- fign of the following flieets is to make this appear ; and to try how far chymiftry will go in fettling the principles of agricul- ture.
I don't intend in the following remarks to fettle fads, or teach the practical part of farming. That I leave to farmers. My defign is only to fketch out the great out- lines of this art, and fhow, that it is ca- pable of being reduced, like others, to a regular fyftem. If in this way we can fix fome fettled principles from the facts which are already afcertained, thofe who apply to practice will find their benefit in it. The juft theory of an art leads directly to its im- provement, as it leads to thofe experiments B 3 which
6 T^be Principles of Part I.
which yet remain to be tried. Without this guide we may Humble on truths by accident ; but when led by it, we have the fecret fatisfaction of thinking, that we are indebted to ourfelves for the happy ilTue of the experiment.
LET us try to find ibme fixed point from which we may have a full view of this extenfive art, and from which we may proceed, in a methodical manner, to the divifion of our fubjec~t. All organized bodies receive their increafe from the recep- tion and application of certain particles, which are defigned by the Author of na* ture for their nourishment. Without thefe nutritive particles there could be no in- creafe. As plants belong to the clafs of organized bodies, they thrive in proportion to the quantity of nourishment they receive at their roots. Hence arifes a fimple, but very comprehenfive, view of hulbandry. The whole of the art feems to centre in this point, viz. nourHhing of plants.
BUT
Sect. I. Agriculture and Vegetation. j
BUT how can the farmer understand the art of nourishing plants, unlefs he knows the nature and qualities of each kind of foil, whether it be proper or improper for that office ; unlefs he can provide fuit- able food for the nourishment of plants, and difcovers what that food is -, unlefs he affifts the plants in reaching and acquiring that food, by rendering the foil loofe and open ; unlefs he knows, and endeavours to remove, Ib far as lies in his power, all im- pediments to this nourishment ? Thefe are the great outlines of agriculture. In fol- lowing thefe, then, we (hall divide our fub- jedl: into five parts. i. The nature and qualities of different foils. 2. The nature and qualities of the different compofls. 3. Their manner of adling. 4. The diffe- rent methods of opening the foil. 5. The impediments to vegetation, and their cure*
THE operations of bodies are to be ac- counted for only from their known qualities afcertained by experiment. Reafoning on i 84 any
8 - The Principles of Part 1.
any other plan, can never certainly lead to truth. I mall not, therefore, proceed a fingle ftep without fact and experiments; and when I am not fupplied with them from others, mail endeavour to make them rnyfelf. It is laborious, but it is necelTary.
SECT. II.
Of different foils.
AS the earth is the matrix to which all feeds are committed, and from which all vegetables take the whole, or at leaft the greateft part of their nou'rim- ment, it is proper to begin with an exami- nation of it. As it nourifhes plants with- out the affiftance of art, it mufl contain the food of plants. If we can difcover what is the natural food of vegetables, we fhall the eafier difcover wherein confifts their artificial food, or that given by art, and how it operates.
EARTHS
Sect. II. Agriculture and Vegetation. 9
EARTHS are found to differ very much from one another in their qualities ; far- mers have therefore divided them into fe- veral different kinds, and perhaps have run into too minute divifions. It is dif- ficult indeed to fettle the exact limits be- twixt the different foils -, but fuch difficulty we find in all the divifions of natural bo- dies. The Author of nature has connect- ed different bodies by intermediate ones; he has chpfen to act by different grada-- tions, and not by ftarts, that nature may appear one connected whole. The great divifion, or the fpecific difference of earths, may be reduced to thefe fix, viz. rich black foil, commonly called loam or ha/ley foil} clay ; fandy j moffy -, chalky ; and till.
WHEN farmers treat of thefe foils, they generally diftinguifh them from one an- other by the colour, or fome other fuper- ficial quality, which immediately (hikes the fenfes. But colour can never lead to the compofition or principles of bodies, on
which
io The Principles of PartL
which alone their effects depend. Such fuperficial qualities as that, depend them- felves on the conftituent parts of bodies. We mall then endeavour, by experiment, to detecl: the conftituent parts of thefe dif- ferent foils, and (how wherein they differ from one another.
SECT. III.
Of the rick black foil.
1 Begin with this foil, as it is found to contain the greateft quantity of vege- table food, and as all other foils arc richer or poorer in proportion as they contain more or lefs of this.
THIS foil, when frefh dug up, and fufficiently moift, has a very agreeable fmell, which is not felt when it is too dry .or too wet. We are very fenfible of an agreeable fmell in the fields after a gentle Shower of rain, efpecially if a drought has
preceded.
Sed. III. Agriculture and Vegetation. 1 1
preceded. This we attribute to the efflu- via of the plants : but it belongs to the earth, as it is to be felt every where, and ilronger the nearer the nofe approaches the ground. This is probably owing to the volatile falts and oils, which rife toge- ther, in greater plenty, as the natural fer- mentation of the earth is increafed by a « *
due proportion of moifture.
i/. tf •
To crumble when dug up, is a quality peculiar to this foil. In this it differs very much from the clay and fandy foil. The former does not feparatej the latter falls into a powder like fand ; but this feparates into fmall bits. It feems to enjoy that de- gree of cohefion which is fitteft for fup— porting vegetables, and ;at the fame time allowing their fibres to fpread in fearch tif their food. The particles of this foil feem to be in a continual tendency to re- cede from one another j for it is obferved, that when dug up, and expofed to the air, the hole from which it was taken, will not
again
1 % ^Ls Principles of Part I.
again contain the quantity taken out. This muft be owing to a fermentation of the putrefactive kind, carried on, in a fmall degree, in thefe rich foils, whenever the
o '
air is admitted to them : for without air there can be no inteftine motion. This continual tendency to putrefaction, in Ibme of the particles of this foil, will appear more plain from its colour, and quantity of oil, the only fubject of corruption. Hence it follows, that there muft be a de- gree of heat in this foil, in proportion to the progrefs of the putrefactive fermenta- tion, and independent of the fun, or na- tural heat of the internal parts of the earth.
THIS foil admits the water eaiily, and fwells like a fptinge after it has taken the rnoiflure in. This quality is peculiar to good foil. It contracts again when dried. Hence naturalifts conclude, that this foil confifts of fpungy and fwelling particles. I rather chufe to attribute this fwelling to the
fer-
Sect. III. Agriculture and Vegetation. 13
fermentation, or interline motion, which continually goes on in this foil, being , inr creafed by the addition of the water : for all bodies muft have a certain degree ol \vatry particles, in order to make the fer- mentation go on properly.
IT is obferved of all foils, the moiTy and boggy ground excepted, that the blacked are the richeft. This' colour gives it§ a ftrong prefumption, that thefe foils con* tain much fat and oleaginous matter; for all foffil and vegetable oils, when they have a great admixture of eartl;, are of this co- lour. It is owing likewiie to thefe oils, that all vegetable or animal fubftances gain a black colour when in the road to putre- faction, The unctuofity too of this foil, a quality of it which is remarked by farrjnr ers, is a proof of its oleaginous nature. This black colour will make it reflect fewer of the fun's rays, and fo make it tible of a greater heat, than .foils are of a lighter colour,
Bt
14 *flx Principles of Part I.
BUT we have a certain method of know- ing, whether a body contains any oleagi- nous particles or not, by the means of nitre melted in the fire. Nitre, though not in- flammable of itfelf, becomes, in this fitua- tion, inflammable, or, as the chymifts chufe to call it, deflagrates with bodies which contain any oily particles.
Exp. i. Some rich mould taken up three or four inches deep from the border of a garden where no dung had ever been laid, deflagrated very much with nitre in fufion. Hence it appears, that this foil contains much oil.
To difcover if this earth contained any abforbent or alkaline particles, I tried the following experiment.
Exp. 2. Some ftrong vinegar, diluted with twice its quantity of water, being poured on this fat earth* raifed a gentle fer- mentation, from whence many air-bubbles
arofe ;
Sect. III. Agriculture and Vegetation 1 5
arofe ; the acid tafte was at leaft deftroyed, and the vinegar reduced to a neutral body. From this experiment we learn, that rich mould contains a great many particles which attract acids, and with them make a neutral fait. I have learned from many different trials, that all foils fit for the nou- rimrnent of plants, contain more or lefs of thefe antacid particles.
To difcover what we mould get from this earth by diftillation.
Exp. 3. I diftilled half a pound of it with a gentle heat j I got in two hours an ounce of a yellow empyreumatic liquor, which was of an alkaline nature. The ftrongeft fire continued for nine hours longer, gave half an ounce more of a yel- lowilh empyreumatic liquor, which had feveral oleaginous filaments fwimming in it. It fmelt like ipirit of hartfliorn, turned fyrup of violets green, and effervefced firongly with vinegar,
FROM
j 6 ^Tbe Principles of . Part I.
FROM this experiment it appears, that the falts of this foil are of the volatile al- kaline kind ; and that thefe falts naturally exift in it, as they rife with a fmall degree of heat. From this likewife we have an- other proof of oil being contained in this foil, as it tinged the firft water with a yel- lowifh colour, gave it a burnt fmell, and was plainly to be difcovered in the fecond floating about in a filamentous way.
SECT. IV.
Of -the day foil.
THE clay foil is very different from the former ; and as it is a compofi- tion of clay with a mixture of the former foil, we mail inquire into the properties of clay.
THE diftinguiihing and char act eriftical property of this body is, that having al- ready got a certain quantity of moifture, it
refills,
S£ct. IV. Agriculture and Vegetation. 17
refifts, in fbme meafure, the entrance of more water into its pores, is very flowly pe- netrated by that fluid, and therefore is not in any great degree foftened, loofened, or otherwife affected by it. Clay, when preff- ed by external force, or firmly compacted by its natural fubfidence, as we find it at the bottom of many of our foils, and of moft of our moiTes, will even fuftain water, and become impenetrable to it. Hence foils, in proportion to the quantity of clay they contain, will hinder the water from paffing through them j will keep the vege- tables continually fbaked in moifture ; will not be fb much heated by the rays of the fun as if they were dry; and, therefore, are juftly deemed of a cold nature.
WHEN expofed to the degree of heat of a fummer fun, clay dries, and turns very hard, fo that it requires a confiderable force to feparate its parts. This quality of clay is the more obfervable, if it has been full of moifWe, and dried fuddenly. Hence C clay
18 *fl>6 Principles of Part I.
clay grounds are fo apt to cake with heat, especially if they have been ploughed wet, and will, in that flate, hinder the roots of vegetables from paffing through them.
THE SE qualities of clay feem to depend on the fame caufe, viz. the ftrong adhefive power of its particles. Its great ductility fhows, that its particles adhere very firmly. But whence this adhefion ? Is it from a certain figure of its particles, by which they are intangled, and can it be fo eafily feparated ? or is it from oleaginous particles mixed with the earthy, as we know that oil is adhefive, and rejects water ? I incline to the latter opinion, as I have found that clay contains an oil, not fo loofe indeed as in the former foil, but intimately con- nected with its earth, and fcarcely fepara- ble from it.
Exf. 4. I mixed forne clay with vinegar; but there was no fermentation, and the acid tafte was not blunted. It feems then to
have
Sect. IV. Agriculture and Vegetation. 1 9
have neither alkaline nor abfbrbent parti- cles in its competition. In this it differs very much from the former foil.
CHYMISTS generally affert, that clay contains an acid of the vitriolic nature, and an oil. From this acid they account for its diftilling the acids of nitre and fea-falt, and for its vitrefcible nature, as falts are the great affiftants of vitrification.
LEMERT le fls, in the Mem. acad. de Selene, four /' annee 1708, has thefe words. Comme il y a dans ? argllle de par- ties huilleufes, acidesy et terreufes. And again, Car en la poujfent par une feu plus confide- rable, il sen cchappe des acides et de parties huilkufes. Let us fee how far this is true,
THAT I might difcover its contents by diftillation,
Exp. 5. I put into the retort half a pound
of dry clay, taken up feven feet below the
C 2 furface
Principles of Parti,
furface from a clay-pit then employed in a brick manufactory ; and as much fand was mixed with the clay, it feemed to be of a pure nature. After it had been diftilled for two hours with a gentle fire, I got half an oz. of pure water. After it had fuffered the ftrongeft heat that I could give it in a port- able furnace for nine hours, I found in- the receiver two drams of a pellucid liquor, which fmelt like the fpirit of hartfhorn, ef- fervefced ftrongly with vinegar, and turn- ed fyrup of violets green. The remainder was very red.
THUS, inflead of getting an acid, as the chymifts aflert, I have got an alkaline vo- latile fpirit. No oil appears from this ex- periment j and, therefore, we may con- clude, that if there is any oil in it, that oil is intimately united and combined with its earthy parts, analogous to what happens in metals.
THAT
Sect. IV. Agriculture and Vegetation. 2 1
THAT there is fuch an oil, feveral rea- fons induce me to think -, its nourifhing ve- getables, which require oil, when opened by mere fand ; its unctuofity -, its igniting, like metals, when put in the fire.
Exf. 6. I tried fuch clay as I ufed in the former experiment with melted nitre. When fmall pieces were put in, no fire was pro- duced betwixt it and the nitre : but I evi- dently perceived fparks of fire when it was put in powdered. Hence I conclude^ tha$ clay contains an oil intimately and clofely combined with its terreftrial parts.
THE oleaginous nature of clay is clearly demonstrated by an experiment of Mr. Eltcrs, in the jth Vol. of the Berlin Me- moirs. He boiled fome clay in an alka- line lye; this lye when decanted was fa- turated with ol. vitriol. After the liquor had flood fome time, he found at the bot- tom a vifcid matter which deflagrated with melted nitre, and reduced the calx of lead C 3 to
22 The Principles of Part I.
to its metallic form By this experiment the oil was got in a feparated ftate from the earthy parts, which after this feparation had loft their tenacity. This gentleman's experiments {how us how ftrongly the oil and earth adhere ; for the oil was fcarcely feparable by fpirit of wine.
Exp. 7. When a piece of the clay was kept in the kitchen-fire for fome time, it turned red like a live coal, and when taken put, had a high red colour, which feemed owing to the particles of iron that it con- tained. Very few particles indeed were at- tracted by the magnet. But it muft be re- membered, that this quality depends upon the inflammable part of that metal, which is always given it by art, and that I had not added oil in the calcination. Very few ores have this quality naturally. All thefe experiments were made on the fame clay.
:. V. Agriculture and Vegetation.
SECT. V.
Of the fandy foil
THi s foil gets its name from the quan- tity of fand which it contains. The qualities of this foil depend on the qualities of fand. This body differs much from the two former j from the latter, as it eafily admits the entrance of water; from the former, as it does not detain the water like it, which feems to attract moifture with con- fiderable force, and to refift its efcape again ; while fand allows it to pafs eafily through its body, and does not fwell, but, on the contrary, turns lefs in bulk, when wet. Sand cannot detain the water fo long as the rich foils, becaufe it does not contain thofe faponaceous and mucilaginous juices which thefe do, and with which the water is combined and detained. Hence fandy foils often want a fufficient quantity of moi- fture for the nourishment of plants. Hence C 4 they
i£ *fhe Principles of Part L
they are very hot, becaufe fand is fufcep^ tible of a greater heat from the influence of the fun, and will retain it longer than water does.
SAND cannot fwell by the addition of water -, becaufe that quality in rich foils is owing to an intefline fermentation, which goes on in them. But in fand there are no particles, and in fandy foils too few, which are capable of fermentation. Hence a de-^ feet of nutritious particles in fandy foils, Inftead of fwelling, it diminishes in bulk when wet 5 becaufe the water rufhing in, difpofes the particles more regularly, fb that the interftices are better filled up than before, and its bulk leflened.
THE faults, then, of the fandy foil are, that it lets water pafs through it too eafily, and that it contains too few nutritious particles. Whatever compofl is ufed to this foil, muft correct one or both of thefe faults. Clay will help it to retain the wa- ter 5
Sect. V. Agriculture and Vegetation. ft 5
ter ; but then it is not richly ftored with ve- getable food. Woollen rags anfwer both purpofes very well, as they contain a great quantity of mucilaginous juice, which ferves equally well in nourifhing plants, and in detaining moifture,
THE compoft that appears to me to be one of the fitted is mofs : for it is as im- pervious to water as clay, nay perhaps more fo j and as it is a vegetable, contains more oil than any other that I know. This reafoning is confirmed by fact. A gentle- man laid fome of this manure on a fmall part of a field, confifling of a very light fandy foil. The oats which grew that year, and the clover which grew the following, were much better on that part than on the reft of the field.
7f* .
THE following experiment was tried on equal portions of about three feet fquare, in a very light fandy foil, during the laft
fummer,
26 T&? Principles of Part. I,
fummer, which being very dry makes the experiment more conclufive.
Exp. 8. N° i. was covered and incorpo- rated with two inches deep of clay. N° 2. with three inches. N° 3. with four inches. N° 4. had two inches of clay with the common quantity of lime laid on ground. N° 5. had three inches of clay with the fame quantity of lime. N° 6. had four inches of clay with the fame quantity of lime. N° 7. had two inches of clay with the ufual quantity of dung. N° 8. had three inches of clay with the fame quantity of dung. N° 9. had four inches of clay with the fame quantity of dung. N° I o. had fix inches of clay. N°. 1 1 . had the fame with lime. N3 12. had the fame with dung. N° 13. was the light poor fandy foil without any addition. N° 14. had the ufual quantity of lime added to the foil. N° 15. had the ufual quantity of dung added to the foil.
July 2.
Sect. V. Agriculture and Vegetation. 27
July 2. N° i, 2, 3, 4, 5, 6. are all bad. N° 7. very good. N° 8, 9. exceeding good. N° 10, 1 1. very bad, N° 12. ex- ceeding good. N° 13. is the worft of all, and fcarcely bears any thing, N° 14. bad. N° 15. pretty good.
Augul 13. N° i, 2, 3, 4, 5, 6. bad. N° 7, 8, 9. exceeding good and heavy grain. N° 10, n. are all withered. N° 12. exceeding good. N° 13, 14. carries no- thing, N° 15. pretty good.
FROM this experiment the following ufeful conclufions arjfe,
Corol. i. A poor fandy foil, when of itfelf it was able to produce no grain in a dry feafon, was fructified to a confiderable de- gree by dung alone ^ but clay alone, and lime alone, did it but very little fervice,
Cor. 2. Light fandy foil is not much benefited by a mixture of clay and lime;
but
Principles of Part I.
but clay and dung enrich it to a prodigious degree, and make it capable of bearing a dry feafon, which of itfelf it can fo little (land. While all vegetation was ftopt in the foil alone, an addition of clay and dung produced one of the beft crops that I ever faw.
Cor. 3. Though thefe conclufions agree in general with regard to all forts of grain, yet as different kinds were fown, I ob- ferved that oats agreed better with clay, and clay and lime, than either barley or peafe ; but that the two laft agreed better with the clay and dung than the oats.
SAND, however hard it is, feems to be moftly compofed of a mucilaginous, oily fubftance; as appears by the following trial.
Exp. 9. February 9. I put ten gr. of pure fea-fand, pounded in a mortar, into a phial with one drachm of oil of vitriol ; the fame
quantity
Sedl. V. Agriculture and Vegetation. 29
quantity of fand with the fame quantity of fpirit of nitre, in another glafs ; the fame with fpirit of fea-falt, in a third. March 28. the acids appeared turbid. I mixed with each fome water, that I might get the fand eafier away by itfelf, and that the particles mixed with the acids might be more eaiily feparated. The fand in the firft glafs weigh- ed 7 gr. 5 and that in the fecond and third, 64: gr- That I might precipitate from the liquors whatever was diffolved by the acids, I mixed with each as much pearl ames as was necelTary to faturate the acids. After the efFervefcence was over, there was a brownifh oozy powder at the bottom of the ol. vitriol, and an oily fubflance at the bot- tom of the other two, which was quite dif- tincl: from the water. What was precipi- tated from the fpirit of nitre, was yellow ; from the fpirit of fait, was white. The for- mer, when feparated from the water, defla- grated with melted nitre, which mowed it to be of an oily nature ; but the latter did
not.
30 ¥he Principles of Part I*
not. I muft obferve here, that the fine powder of flint has a fenfible deflagration with melted nitre.
As lime is a powerful diflblvent, eipe- cially of oily bodies, I imagined that lime might have fome fuch effect on fand, dif- folve it into a mucilage in the earth, and in this way fand might be converted into a fit nourimment for vegetables. This per- haps might be, I thought, the reafon why lime and fand took fo firm a bond toge- ther, when lime alone does not adhere. This appeared to me yet ftronger, when I confidered, that any mucilaginou's or oily fubftance, fuch as whites of eggs, train-oil, &c. when mixed with quick-lime, make it take bond. I therefore tried the following experiment.
Exp. 10. I took a certain number of fmall pieces of flint, which is allowed to be of the fame nature with land, weigh- ing i dr. 52ir gr. and added a quantity of
lime
Sect. V. Agriculture and Vegetation. 3 1
lime and water to them. They lay amongft the lime from the 9th of February to the 23d of March. When taken out, and dried, they weighed the fame as when put in.
Exf. 1 1. That I might fee what effect the mucilage extracted from fand by the acids, would have on quick lime, I added a very fmall quantity of the mucilage from both acids to quick-lime, and baked them together into a pafte. Some of the fame, lime was made into a pafte with water alone. After they had lain for four weeks, and were entirely dry, neither of them had taken bond.
THESE experiments would feem to be in oppofition to the former theory. The queftion, however, is of fuch ufe, efpecially with regard to building, that it deferves to be further confidered.
SECT,
32 "The Principles of Part I.
SECT. VI.
Of the chalky foil.
I SHALL fay little about this foil, becaufe, as it is to be found only in few counties in England, I have not yet met with it; and I (hall relate nothing on the faith of thofe who reafon without the afliftance of experiment.
CHALK is an abforber of acids, and has no oleaginous particles in its compo- fition, but is a powerful attracter of them. Hence the proper manure for this foil muft be thofe bodies which contain moft oil, as hair, rags, &c. It feems to have but a very weak attraction to water ; and, there- fore, will be generally too dry. This foil is obferved by farmers to cake after heavy rains.
SECT.
Seel. VII. Agriculture and Vegetation. 33
SECT. VII.
Of till.
FARMERS call thofe foils til/, which have a reddifh, gray, or yellowifli co- lour, are poor, will bear nothing, nor can be fertilized fo eafily or fpeedily as the for- mer foils. Sometimes they render all at- tempts fruitlefs. This icil muft, therefore, not only contain no vegetable food, but it muft often contain a vegetable poifon; elfe it would always become fruitful by the ap- plication of comports. What this poifon is, muft be the lubjecl of our prefent inquiry ; for unlefs we know it, we cannot know whether there is a remedy for it or not.
THE following experiments were per- formed on iome of this unfruitful earth mown me by an experienced farmer.
Exp. 12. It efFervefced vifibly with vine- gar and oil of vitriol diluted with water, D but
34 *the Principles of Part L
but had a peculiar irony tafte, and turned black with galls,
Exp. 13. Some of this earth calcined in a ftrong fire for two hours, was almoft all attracted by the magnet.
Exp. 14. It did not deflagrate with melt- ed nitre.
Exp. 15. Four ounces of brown till well dried, being diftilled, in fix hours gave two drams of a phlegm, which {hewed no acid or alkaline nature.
FROM thefe experiments it appears, that this fpecies of till contained neither falts nor oils, but was a competition of earth and iron. The poifonous quality of this foil muft then have depended on the latter bo- dy, which we may obferve by the firit ex- periment is diflblvable in all acids, and in that ftate may enter the veflels of plants. We fhall afterwards fee that it will meet
with
Se<fl. VII. Agriculture and Vegetation. 35
with acids. This reafoning is put beyond all doubt by the following experiment.
Exp. 1 6. I took one pound of good rich mould, and mixed with it one drachm of fait of fteel; put it into a pot, and fowed feme barley in it in the beginning of May. Some of them (hot up about an inch, looked very ill-coloured and fickly, and then died; while other grains in another pot, filled with the fame earth, throve very well.
THUS a very fmall quantity of iron, diffolved by the vitriolic acid, rendered a great quantity of rich eartii unfruitful, and therefore ought to be looked on as the ve- getable poifon of till. If this poifon can admit of a cure, I imagine it is only to be found in lime or marl, which will attract the acids from the iron, and make it, at leaft in a great meafure, indiflblvable in water.
THOUGH the admixture of iron with
the foil may be a very general caufe of un-
D 2 fruit-
36 The Principles of Part. I.
fruitfulnefs, yet it feems not to be the only one. A great deficiency in fome of the principles necefTary for vegetation, muft have the fame effect. Thus farmers often sive
D
the name of //'// to indurated clays, and particularly to thofe which they find below the foil. The common farmer is afraid of ftirring it up with the plough, becaufe it is unfruitful : but the more judicious, will- ing to deepen his foil, takes it up by little and little, and finds that lime, dung, and air, readily fertilife it.
SECT. VIII.
Of the mojjj foil.
I Shall not enter into a difcuffion of the origin and nature of mofs : it is now allowed by every body to be a vegetable fubftance. The following experiment is a proof of it.
Exp. \j. Haifa pound of powdered peat gave me by diftillation, during the two firft
hours,
Sect. VIII. Agriculture and Vegetation. 37
hours, 2 oz. of an acid empyreumatic li- quor, which was of a yellow colour, and ihowed its acid nature, by effervefcing with ol. tart. p. d. The flrongeft fire continued for nine hours longer, gave me 2 dr. of a reddifh empyreumatic liquor more acid than the former, and I fcr. of a thick dark-co- loured oil. There was befides about the neck of the retort, a great quantity of red oil, which was too heavy to come over. The refiduum was black.
Exp. 1 8. Some peat burnt in the open fire, gave me about the two and thirtieth part of alkaline fait.
HENCE we fee, that peat affords the fame principles as other vegetables do, and therefore muft be claifed amongft them.
THE only method, then, to make this foil
fruitful, is to make the vegetable undergo
a degree of putrefaction, by ploughing the
foil, and ib killing the plants. All vege-
D i tables
38 The Principles of Parti.
tables turn to rich foil when they have un- dergone a degree of corruption j even oak bark becomes in time rich black mould. The parts wilt be the fooner feparated, if fome earth or clay is added to the mofs ; for mofs of itfelf is rather an enemy to cor- ruption. All kinds of vegetable fubflances and animal bodies are preferved uncorrupted for whole ages in mofs-holes. Abforbents are known from experience to be promoters of corruption. The various kinds of marl, when they can be got, particularly the mell-marl, would feem to be the propereft manures for this foil. Lime, as it appears to be a great diflblvent of all vegetable bo- dies, may have good effects on this foil.
PART
Sect. I. Agriculture and Vegetation. 39
PART II.
SECTION I.
natural methods of providing vegetable food.
H
A v i N G afcertained the properties of the different foils, the next thing we have to do is, to exa- mine into the nature and properties of what- ever is obferved by experience to fructify ground, whether it be applied to the foil in a natural or artificial way. If we can dif- cover fome qualities in which all thefe ma- nures agree, we fhall arrive at the know- ledge of what we are in fearch of, viz. the food of vegetables, or at leaft of thofe prin- ciples which go to the compofition of that food. Let us firft inquire into thole ways by which nature fructifies the earth.
D 4 IF
40 *fbe "Principles of Part II,
IF earth is exhaufted of its vegetable food, experience has difcovered, that it re- covers it again, if allowed to lie idle. This fhows, that the vegetable food is continual- ly on the increafe, when the earth is not robbed of it by the crops it bears. We dif- cover immediately whence this food comes, when we attend to thefe two fads j . that the more the foil is expofed to the air, the vegetable aliment is the fooner procured, and in greater quantity too ; and that when the furface is buried by the action of the plough, and a new foil brought up, that foil, though feemingly as good as the for- mer, produces bad crops, till it has re- ceived for fome years the benefit of the at-» mofphere.
FALLOWING is a conftant proof of this. The foil is frequently broke down and turned over by means of the plough, and every part of it is expofed to the influence of the air. That the communication of the earth, by the mechanical a&ion of the
plough,
Sett. I. Agriculture and Vegetation. 41
plough, is not the chief means of increafing the vegetable matter, as T#// aflerts, appears plainly from thefe two fads ; that even the lighter!: foil is the better of fallowing ; and that when fallow ground is laid up in ridges, more benefit is received than when it is left quite flat.
BUT this nutritious influence of the air is yet more obfervable in thofe earthen dikes or walls made of the foil taken from the furface, and thrown up to inclofe the meep- folds. Thefe dikes are expofed to the in- fluence of the air, which pafTes through and through them for many months. The foil thus expoied is rendered prodigioufly fruitful, fo that it is eafily diftinguimable by the quantity and deep green colour of the grain, from the internal parts of the fold, which have been well manured by the urine and dung of the fheep. It is likewife remarked by farmers, that the earth of the dike lafts for three or four
years
Principles of Part II.
years longer fruitful than the other part of the iheep-fbld.
THIS chief inftrument, then, that nature makes ufe of to enrich the earth, is the air. Even the richeft foils require its continual influence. On what principles of the air this fructifying quality depends, we cannot inquire, until we have afcertained the na- ture of the different manures which feem to operate by attracting thofe principles from the air. The flrong and lafting vege- tative power which the air communicates to the earth, mould teach us to make a greater ufe of its influence than what we do. Why mould we not raife the whole furface into fold-dikes ? Other manures do not operate till the fecond or third year after they are laid on ; this operates imme- diately. A farmer cannot, at a medium, dung an acre under _$/; this might be done for 30*. Dung fills the ground with weeds; this method cleans it. Manures cannot be found every where 5 this practice
may
Se<5t. I. Agriculture and Vegetation. 43
may be followed in all places. It would be particularly good for clay ground, as the viciffitudes of the air pulverife greatly.
D E w is reckoned by farmers a great fer- tilifer of the earth. It arifes from the per- fpiration of the earth, of vegetables and animals in a found ftate, and their exhala- tions in a corrupted one. The earth re- taining its heat, after the fun's influence is weakened, elevates thefe attenuated par- ticles : but the air cooling fooner than the earth, from its rarity, condenfes them at a little diftance from the furface ; and thofe which become fpecifically heavier than the air, fall on the earth again. Hence dew muft differ according to the difference of the bodies from which it proceeds. Its contents are therefore various ; but experi- ments have difcovered, that it is compofed in general of oils, fairs, and a great pro- portion of water. Of what ufe thefe prin- ciples are to vegetation, we mail after- wards fee.
RAIN-
44 2fo Principles of Part II.
RAIN-WATER, efpecially in the fpring, has nearly the fame contents. Margraaf, in the Academ. de Berlin, vol. j. has ana- lyfed it with great accuracy, and mowed that it contains a nitrous and a fea-falt, with a confiderable quantity of an abforbent earth j which probably was united to a nitrous acid before evaporation, and con- fequently increafed the quantity of nitrous fait very much. The falts were of a brown colour, which difcovered its oil. As the water was gathered in the winter, it con- tained a fmaller proportion of this laft body, than if it had been gathered in the fummer.
SNOW is juftly reckoned amongft thofe bodies which frudlifv earth. I have obferved
j
a light floating oozy fediment at the bottom of fnow-water, after I had kept it three or four days. When fnow melts, its furface, ' even in the tops of hills, is covered with a brown powder, Bath rain and fnow-water putrify fconer than fpring water j which
{hows
Seel. I, Agriculture and Vegetation. 45
fhows that they contain more oily particles than it do.s.
Exp. 19. A pound and an half of fnow- water being evaporated, gave 2 dr. of a reddifh liquor, which had little tafte, and difcovered nothing faline in it. I fet it in a cellar for fourteen days j and when I took it out, it was covered with a mouldy fub- fiance. This mould, when dried, burnt on a red-hot iron to a powder. Hence it ap- pears, that fnow contains an oily fubftance, Margraaf having evaporated a greater quan- tity of fnow- water, difcovered the fame falls* and earth as in rain-water.
THE overflowing or water-flooding of low grounds may be reckoned amongft the natural methods of improving the foil; becaufe fiat meadows are often naturally overflowed, either by rains, or by the rain- water falling from the higher grounds. Egypt is naturally overflowed once a-year by the Nt/e, and rendered by that means
exceedingly
46 The Principles of Part II.
exceedingly fertile. Spring-water is even found to be of fervice to ground, but not fb much as river-water, especially fuch as has run through a fertile country, and is, at that time, full of the fubtiler particles of the .foil warned off from the rich grounds by rains. As thefe waters are impregnated with the fubtile earth, and the faponaceous juices of thofe foils over which they have run, when they ftagnate, thefe nutritious particles fubfide, and inrich the ground. The river Nile depolites a rich oozy mud, which is fo full of putrefcent particles, that its fleams feem to be the caufe of the plague raging fo much in Egypt. By this addition of foil it receives every year, the level of the ground is confiderably higher than it was. Hence too the vallies in all countries are much • richer than the rifing grounds ; as the rains warn great part of the vegetable matter from the latter, and leave it in the former.
ART
Sect. I. Agriculture and Vegetation. 47
ART often imitates nature in this me- thod of improving land, and lets in the ftreams of rivers to cover the fields. This is moft frequently done in the fpring, when thefe waters are moft impregnated with nutritive particles. This water, after it has depofited all its particles, which it does in four or five days, is let off quickly ; left, by a gradual evaporation, it fhould cake the ground, and hinder the grafs to come up ; which is the great danger attending it, and for which it is thought improper for clay grounds.
IT muft be obferved here, that there are fome waters which are extremely preju- dicial to grounds, fuch as coal and fteel waters. This is owing to the quantity of iron which both thefe contain. All fulphur waters are likewife hurtful to ground ; we fhall afterwards fee that fulphur is a poifon to plants,
SECT.
48 'The Principles of Part II.
\
SECT. II.
Of manures, or the artificial methods of pro- viding vegetable food.
EXPERIENCE has fhown, that cer- tain fubftances, committed to the earth under certain regulations, make it more fruitful. Thefe fubftances belong either to the foffil, the vegetable, or the ani- mal kingdom. The foffil include the dif- ferent kinds of marl j calcarious ftones, fuch as lime-ftone, chalk, &c. j and quick-lime. The vegetable include all vegetables, and their juices, either in an intire or a cor- rupted ftate ; the afhes of burnt vegetables ; the oils extracted from vegetables and loot. The animal include calcarious (hells, intire or corrupted ; horn-fhavings or tips j wool- len rags 5 and all animal fubflances, fuch as dung, urine, &c. 1 {hall treat of thefe in their order.
Sect. III. Agriculture and Vegetation. 49
I am not to lay down the method of ufing thefe ; I mail take no notice of that, but where it tends to mow their method of ope- rating. My defign is to take a view of thofe qualities belonging to them, by which they are capable of operating on the foil, and producing certain effects on the vegeta- tion of plants.
SECT. III.
Of marl.
TH I s is a foffil body which feels unctuous and fat betwixt the fingers ; and refembles clay in a great meafure, info- much that marl, though a very different body, is often confounded with it. It is divided into many different kinds, which may be all included under thefe two, clay, and Hate or ftone marl : for what is com- monly called Jhell-marl, is an animal fub- ftance, and therefore to be claffed amongft
E them,
50 The Principles of Part II.
them. The different colours of marl make no real difference as to their properties.
Exp. 20. It is a diftinguiming and cha- ra&eriftical property of this body, that, when it is put into water, it falls down into a powder. The clay marl dilfolves much quicker than the ftone marl. This quality muft be owing to the weak adhe- lion of its particles j fo that the fmall force with which water enters its pores, is capa- ble of feparating the particles of the marl. By this property it is fufficiently diftin- guifhed from all the earths which we have mentioned ; and particularly from clay, which does not fo ipeedily admit the en- trance of water.
A s marl is fb much opened by water, fo as to lofe its natural cohefion entirely, we fee how much it will favour the efcape of water from fuch grounds as have been ma- nured with it. Clay grounds, after they
have
Sect. III. Agriculture and Vegetation. 5 1
have been marled, become much drier. It is owing, I imagine, to the water get- ting off fo quickly, that marled grounds, as is obferved, are lefs affected by froft, than the fame foils which have not got any marl.
Exp. 21. It effervefces with all the dif- ferent acids, and turns with them into a neutral fait. During the effervefcence with the oil of vitriol, a fulphureous fleam arofe, which is a flrong prefumption of its con- taining fome oily fubftance. The clay marl feemed to diffolve fafter than the ftone marl, and deflroyed about a third more of the acids. This quality which marl has of at- tracting and destroying acids, is one of its diftinguiming properties, without which no fubftance can be called marl. In this quality it is likewife diitinguifhable from clay.
As farmers are extremely inaccurate in
their terms, they often give the name of
E 2 marl
52 The Principles of Part II.
marl to bodies which do not effervefce with acids. That fuch fubftances may and do fructify ground, is indubitable > but they ought not therefore to be called marl. Surely bodies which do, and bodies which do not effervefce with acids, are very dif- ferent in their nature, and ought to have different names. As the name of marl, then, is generally, fo let it be only applied to the former clafs. The latter mould have fuch names as will diftinguifh them from the former. This mews what con- fufion there is in the terms of agriculture, and how much they ftand in need of being defined.
Exp. 22. Another quality belonging to marl, by which it is diflinguilhed from clay, is, that it cannot be converted to brick. It is indeed very much altered by a ftrong heat; it lofes its antacid quality while it remains unpowdered ; and is no longer difiblvable in water, as it was be- fore:
Seft. III. Agriculture and Vegetation. 53
fore : but {till it is very different from a half-vitrified fubftance ; and I much quef- tion, whether or not it can, without any addition, be turned into glafs. This is a ftrong proof, that it contains no falts, acid, alkaline, or neutral ; for thefe are capable of vitrifying lime when added to it.
Exp. 23. I could not get any fait from thefe marls, either by fimple lixiviation, or diftillation, though I urged them with the ftrongeft fire. The fire feparated nothing but a little water, which appeared to be gently alkalefcent j owing perhaps to fome of the finer marly particles, which were carried up by the water. No oil appeared in the diftillation. When the powder of marl was thrown on fufed nitre, it fparkled a very little. This, and the fulphureous fmell arifing when it was diffolved by the oil of vitriol, would incline me to think, that it has a fmall proportion of an oleagi- nous matter in its compofition.
4
£3 BUT
54 - TZtf Principles of Part II.
BUT though perhaps it contains none, yet it ftrongly attracts all oils. This is a quality which the chymifh know belongs to all abforbent earths ; thefe they make ufe of to feparate oils from other bodies. Hence it will attract and fix the oils which it meets with in the ground, which fall with the fnow and rain ; and even thofe which, floating in the air, touch its furface.
To inquire a little further into its na- ture, and feparate its antacid parts from the others, that we might difcover both ; Exp. 24. I took half an ounce of ftone marl in powder, and faturated it widrfpirit of nitre, by adding the acid in fmall quan- tities for five days j the faline liquor was filtred through brown paper. There re- mained in the paper three drachms of a bluifh adheiive earth, which, on trial, ap- peared to be a fine clay. To recover the other part from the faline liquor, I added oL tart. p. del. till no more lactifcency ap- peared -3
Sect. III. Agriculture and Vegetation. 55
peared j a white fubftance fell to the bot- tom, and was feparated from the liquor by filtration. This powder being wafhed with water, that all the falls might be feparated from it, and calcined in a ftrong kitchen-fire for five hours, gave me a quick lime, which afforded good lime-water.
FROM the fame quantity of clay marl, treated the fame way, I got three drachms and twenty-eight grains of clay, and thirty- two grains of a calcarious earth.
FROM the fame quantity of clay marl, faturated with vinegar, and treated the fame way, I got two drachms and fifty-nine grains of clay ; and the remainder was a calcarious earth, which, being burnt, afford- ed good lime-water.
THE fame quantity of a different clay
marl, treated the fame way, afforded two
drachms and fifty-four grains of clay, and
one drachm fix grains of a calcarious earth.
E 4 THE
56 Tloe Principles of Part II.
i
THE fame quantity of ftone marl, treat- ed the fame way, afforded juft the fame proportion of clay and calcarious earth.
MARL, then, is a body compofed of lime and clay in different proportions, according to the different kinds of marl, and generally about one fourth of lime and three fourths of .clay.
FROM this experiment we may eaiily account why marl falls in water, as lime ftrongly attracts water -, and why it lofes this property when burnt, as clay becomes more tenacious by fire ; why it cannot be converted to brick, as the lime hinders that clofe adhefion of the particles of clay which is neceiTary to conftitute brick ; why it will not vitrify, as lime is an enemy to all vitrifi- cation j and why it mews a fmall portion of oleaginous matter, as clay contains fome oil. By mixing quick or rather effete lime with clay, or a clay foil, we imitate, in
fome
Sect. III. Agriculture and Vegetation. 57
fome meafure, this production of nature, but fall vaftly fhort of her in the equality of the mixture, and perhaps to in the fub- tility of the particles.
THERE is a body very ilmilar to marl in its appearance, but very different from it in its effects, and often found in the fame bed with the beft marl. It is of a darkim lead colour. Inftead of fertilizing ground, it renders the beft foils incapable of bearing any kind of vegetables for many years. I have feen the fpots on which it was laid entirely barren three years after. I have heard of its effects continuing in other places for a much longer time j nor is it certainly known when its bad effects' will end. A body fo very deftru&ive to agriculture, de- ferves to be well charadterifed, in order to be munned ; and well examined, that we may know whence proceeds this noxious quality, and how to cure it when it has taken place.
THOSE
$S The Principles of Part II.
THOSE who have been much ufed to marl, have already difcovered a difference betwixt it and this body. The former, they obferve, takes a fmooth polifh from the inftruments with which it is wrought, but the latter does not. As this quality alone is fcarcely fufficient to diftinguim thefe two bodies from one another, let us apply to experiment for more.
Exp. 25. If a piece of ijt is taken up which has not been much expofed to the influence of the air, it differs very much in tafte from marl. Inftead of the fmooth unctuous tafte of the latter, it is acid, and remarkably aftringent.
IT agrees with marl in falling down into a powder in water ; but then it differs re- markably from it, in raifing no affervefcence with acids, nor in the leaft deftroying their acidity.
IT
Sect. III. Agriculture and Vegetation. 59
IT turns the fyrup of violets red j which (hows, that it contains an acid : whereas marl, like all abfbrbent earths, gives it a green colour.
THESE qualities are fufficient to teach the farmer how to diflinguifh this poifon- ous body from marl, and how to fhun it. Let us now try if we can difcover on what principles this poifonous quality depends ; for if we can inveftigate its nature, we may perhaps find out a cure for it. Befides, all purfuits of this kind lead us directly to the true fyftem of vegetation. The vegetable is like the animal body, whofe nature is afcertained as well by what does it harm, as by what does it good.
FROM my experiments in die fedtion on till, I imagined that its poifonous quality might depend on its containing fome fait of iteel. I, therefore, directed moft of my trials on this body with that view.
Exp,
60 'The Principles of Part II.
Exp. 26. Some of it was infufed in warm water. The water had a greenim colour, tafled gently acid, and very aftringent. It gave the fyrup of violets a pale-red colour. OL tart. p. d. dropt into it made no (enfible erfervefcence, but feparated fome air-bubbles, difcoloured it, and precipitated a pale-red powder from it. Some of this powder was put into a .crucible, and kept in the fire for half an hour. I could recover but little of it again, and that not quite free from the fubftance of the crucible j yet the magnet attracted fome of its particles, and fhewed that it contained iron. The liquor evapo- rated gave me a tartarus vitriolatus.
THE pure infufion did not alter its co- lour much on an admixture of galls. But this was no proof that the liquor did not contain fait of fteel : for an acid deftroys this efFecl: of the galls ; and the liquor, as we have already found, contained an acid. To deftroy the acid, I poured in ol. tart.
p. d.
Sect. III. Agriculture and Vegetation. 6 1
p. d. into the mixture of the infufion, and galls ; it took immediately a brownifli co- lour, and afforded a plentiful precipitation, which, in twenty-four hours, had taken a purple colour.
I boiled a quantity of the earth for half an hour in water, flrained and evaporated it. A white faline fubflance remained in the proportion of 6 grains to each ounce, which tafled exactly like fait of fleel. This fait difTolved in water, turned fyrup of vio- lets green, as does fait of fleel ; and took a deep black colour with galls : Sufficient proofs of its being fait of fleel. Nor cart its white colour be any objection ; for fait of fleel reduced by trituration, evaporation, &c. to a powder, is white ; and the fait which I procured, was a powder.
IT appears, then, beyond all doubt, that this fubftance confifls of an earthy body like clay, about an eightieth part of (alt of fleel, and a fmall proportion of the
« vitriolic
62 TZtf Principles of Part II.
vitriolic acid. From other experiments which I have made, the bad effects do not feem to arife from the vitriolic acid ; elpe- cially as the acid here appears to be very volatile. But we have already difcovered the pernicious quality of fait of fleel. Nor is it any wonder, that it mould exert itfelf fo powerfully here, coniidering the quan- tity of this body laid on ground inftead of marl, and the great quantity of this fait in it. The foil muft be perfectly faturated with it.
BUT how mall we correct the poifonous quality, if, by miftake, this or fuch like bodies mould be ufed ? For coal produces the fame effects from the fame caufe. There feems to be no other method but that of decompoiing the fait -t fo that the fteely part may be no longer diffolvable in water. The air, by volatilizing the acid, and leaving the chalybeate particles behind, has that ef- fect, by gentle degrees, on fait of fleel, when it is diffolved in water. But, in the prefent cafe, the acid would not reach the
fait,
Sect. III. Agriculture and Vegetation. 63
fait, unlefs the foil were frequently turned over; and even then much of the fait would be defended by the oleaginous par- ticles of the foil. Marl appears to me to be the proper cure j for that abforbent earth, having a ftronger affinity to the acid of vitriol, than what the iron has, will unite itfelf with the acid, feparate the chalybeate particles, render them infoluble in water, and confequently unfit to enter the vefiels of plants. A conliderble mare of the good effects of marl in all grounds, may, perhaps, be owing to this fpecial effect, viz. the deftruction of a body, which, in proportion to its quantity, deftroys all vegetation.
THERE is another foffil body very fimi- lar to marl in its appearance, and fome of its qualities, and may be miftaken for it. It is called by fome writers foap- rock, from its fimilitude to foap, and its being often found in rocks -, though I have known it lying on the furface in great
quan-
64 Vfe Principles of Part II.
quantity. As none has yet analyzed it, we fhall undertake that tafk.
Exp. 27. It is fometimes of a bluifh, fometimes of a reddifh colour ; and when moifr., feels exactly like hard foap betwixt the fingers.
IT falls like marl when put in water: if it is well mixed with the water, it fepa- rates into different parts from their diffe- rent fpecific gravity j at the bottom there is a layer of large grey particles -, above that are fome darker ; next thofe of a dark brown colour ; and the uppermoft is a light white powder ; a great deal of which was fufpended in the water for 20 hours.
IT effervefces with none of the acids. In this it differs from marl.
Exp. 28. Some of it was lixiviated in water 5 which being evaporated, gave a very little fea fait.
Exp.
Sect. III. Agriculture and Vegetation. 65
SOME of it was calcined for four hours in a flrong kitchen fire. The bluifh remained of the fame colour 5 but the red turned lighter in its colour. The firft contained a few particles, which were attracted by the magnet j the laft almoft none. It fell as foon as the unburnt in water, and with the fame appearances.
I dim' lied four ounces of it in a flrong heat for eight hours, and it gave me only one ounce of pure water.
IT did not detonate with nitre in fuiion, but fome few fparks appeared, which mews that it contains oil.
THIS oil I extracted, by boiling four ounces of it with two ounces of potames for many hours ; to this decoction I added fpirit of nitre, and got a precipitation of a red heavy oil, which detonated with nitre in fufion.
F I took
66 The Principles of Part IL
I TOOK, four ounces of it, and warned off the light earthy parts by mixing water often with it ; in this way I got ten drachms of a whitifh powder, which appeared to be clay. The remainder was compofed of two parts, a fine grey powder, which ap- peared to be fand; and fome large parti- cles, white and green. Thefe did not ef- - fervefce with acids, nor yielded a tindure of fpirit of wine ; but felt foft and undtuous in the mouth, and when boiled with fbap- afhes, and fpirit of nitre added to the lixive, afforded a heavy oil. This mews them to be of an oily nature.
SOAP-ROCK appears from thefe experi- ments to contain near a third of clay, a much greater proportion of fand, and a body of an oily heavy nature.
THAT I might go a little further, and difcover its effects in vegetation, and with what foils it would agree beft, the follow- ing
Sed. IV. Agriculture and Vegetation. 67
ing experiment was tried, though late in the year.
Exp. 29. A pot was filled with the pooreft earth that I could find 5 this I (hall call N° i. N° 2. fame earth with a third of foap-rock. N° 3. very ftrong clay with a third of fand. N° 4. the fame clay with a third of foap-rock. N° 5. foap-rock alone. In thefe pots I fowed barley.
THE plants feemed to grow beil at firfl in N° 2 : but afterwards N° 4. produced the moft. In N° 5. the plants were longer of appearing, and feemed more fickly than the others.
SECT. IV.
Ofunburnt calcarlous bodies , and quick-lime.
CHALK is reckoned, by the generality of writers, a good manure for all wet clay grounds j for it makes the earth loofe F 2 and
68 *fhe Principles of Part IL
and hollow; keeps it dry; and, as the farmers exprefs it, fweetens the foil. The foft un&uous kind is thought the befL Farmers think that it exhaufts the foil very much; and therefore they generally advife dung to be laid on along with it. Lime-ftone gravel is much ufed in Ireland as a manure.
THESE calcarious bodies are not difTol- vable in any way but by acids. With thefc a great efFervefcence Jiappens, a folution of the calcarious body is made, and a neu- tral fait is formed from that conjunction. This neutral fait is always foluble in water,, unlefs where the acid of vitriol is ufed.
THESE calcarious ftones, when burnt in a ftrong fire, turn to quick-lime, a body much ufed in farming. It attrads acids much more than it did before, and is now in a fmall degree foluble in water, without their afiiftance. It is not, however, on thefe foluble parts that its frudifying power
depends ;
Sect. IV. Agriculture and Vegetation. 69
depends ; becaufe it has no fenfible effect, except in killing vermin the firft year, when thefe parts are moft foluble in water. Lime is probably effete, and no longer foluble, when it begins to aft on the ground, and affift vegetation. The lime of old houfes, which is quite effete, is reckoned better than frefh quick-lime.
THERE is a very great attraction betwixt quick-lime and all oily bodies j it unites intimately with expreffed oils. With this intention it is ufed in the manufacture of foap, to help the junction of the alkaline falts and oils. It mutt, therefore, attract the oils powerfully from the air and earth, dif- folve them, and render them mifcible with water: it muft, from this reafbn, loon ex- hauft the foil of all its oleaginous particles, if the farmer does not take care to fupply them by dung or animal fubflances. Farm- ers have by experience difcovered it to be a great impoveriflier of lands, but they did not know how it acted. Its operation is, F 3 to
70 17je Principles of Part II.
to exhaufl the earth of its oils, Lime laid on ground wore out by continual crops, rather hurts it than improves it ; becaufe it does not meet with oil or oleaginous bodies to aft upon, and blunt it. The proper cure for this is, to mix dung with the lime, fo that it may have fomething to aft on.
LIME is a great difiblver of all bodies, both vegetable and animal, but particularly the latter. We know how foon it difiblves hair and woollen rags into a pulpy fub- ftance. This effect is fo flrong, that, in the common method of fpeaking, it is faid to burn them. In this way it certainly ope- rates in the earth, by dilTolving all animal and dry vegetable fubftances, and converting them to the nourimment of vegetables, at leaft fooner than otherwife they would be.
LIME powerfully refifts putrefaction, as is difcovered by many experiments. It does not appear, therefore, very judicious, to mix
quick-
Sect. IV. Agriculture and Vegetation. 71
quick-lime with dunghills, which are not yet fufficiently putrefied, as it muft flop that procefs. When once that procefs is finifhed, many good effects may arife from their junction, and particularly that of hin- dering the oils to be volatilized, and of fix- ing them.
9
IT is obferved of lime, that it is conti- nually falling downwards, fo that, in a few years, the greatefl part of it is to be found lying together as deep as the plough goes. This is owing to its great fpecific gravity.
IT is like wife obferved by farmers, that lime has a better effect on light foils than oa ftiff, for the firft three years, but, after that time, its operation turns much weaker. Light foils are moft pervious to the air; and as the good effects of all manures de- pend on the influence of the air, that in- fluence muft be ftronger in open foils than in thofe which are more compact : but as F 4 that
*fbe Principles of Part II.
that foil has the loofeft texture, the lime falls quickly through it,
BESIDES; by mixing itfelf with the ole- aginous particles of the foil, and convert- ing them to the nourifhment of plants, lime becomes in this fenfe a provocative to the foil. In promoting the work of vege- tation, it will foon exhauft all the oils of the light foils, which contain them but in fmall quantity, and when they are all ex- traneous, for fand can afford none. But a clay foil, containing in itfelf a confide- rable quantity of oil, and that not fo eafily foluble, is not foon exhaufted. An addi- tion of an animal or putrefied vegetable fubftance to thefe light foils, would remedy this defect.
SECT.
Sect. V. Agriculture and Vegetation. y 3
SECT. V. :.
Of vegetables in an intire and in a corrupted Jlate^ and of dunghills.
WE come next to treat of thofe ma- nures which are drawn from the vegetable kingdom. All vegetables, unlefs fome noxious ones, nourifh plants. Malt- duft is reckoned a good manure. Bark of trees, and faw-duft, are recommended by fome writers. We learn from Columella that the ancients laid the lees of their olive oil on the ground, and found it of great benefit. And, indeed, it is not to be won- dered at, that the juices of vegetables al- ready concocted, mould prove a nourimment to other vegetables. But it requires much time, before thefe can be reduced to Ib fmall parts, and fo duTolved, as to be ca- pable of entering the minute veflels of plants. This is moil expeditioufly and moil effec- tually performed by the means of corrup- tion. Hence we may fee the reafon, why
the
ctke Principles of Part II,
the bun or woody part of flax has no good efTed: on ground, as the juices are already extracted, by the previous putrefaction which the flax has undergone in the procefs of fteeping, and little now remains but mere earth,
THE different fpecies of fea-weed, efpe- cially the kelp, are found very ferviceable to land. Thefe weeds are of a foft pulpy texture, and eafily diflblve. Befides, there are no plants which contain fo much fait, and fo much oil, in proportion to their earthy parts. The falts are in fuch quan- tity, that the kelp, though very dry, will not burn ; as all falts, nitre excepted, are enemies to fire. The oils are difcovered to be in great plenty, becaufe this plant, not- withftanding thefe falts, putrefies very foon. The afhes of this plant * confifl of about equal parts of alkaline fait, fea-falt, an oily fubftance, and an earth.
* Vid. Experiments on bleaching, part 3. fe£h 6.
DUNG
Seel. V. Agriculture and Vegetation. 75
DUNG probably was the manure firft ufed by farmers, as all vegetables fponta- neoufly turn to it, and as accident mufl foon have difcovered its good effects. It is the manure at prefent moft ufed. The manner in which it is made, is, therefore, a fpeculation worthy of our attention, and may lead to fome ufeful hints in the ma- nagement of dunghills.
PUTREFACTION is defined by chymifts to be an inteftine motion of a body, whereby the union, texture, colour, fmell and tafte are deftroyed.
THERE is no change fo common in na- ture, as that of bodies from an entire to a corrupted flate. All vegetables, whether acid, acefcent, alkalefcent, auftere, aroma- tic, infipid, cold or hot, are liable to cor- ruption, and generally end in it. The al- kalefcent, fuch as onions, celery, &c. run immediately into corruption, without un- dergoing
76 Tfo Principles of Part II.
dergoing the other two fermentations ; but the acefcent can be made fir/I to ferment into wine, and generally of themfelves un- dergo the acetous fermentation, before they fall into the putrid. Animals are conti- nually in the very confines of putrefaction ; and when death flops the circulation and admiflion of frefh juices, they fall imme- diately into it. Animals, and alkalefcent plants, as they want that acid which abounds in the acefcent plants, have a greater ten- dency to putrefaction, which every one knows is greatly retarded by acids. Next to the excrements, which are already in a ftate of high putrefaction, the blood is the moft putrefcible fluid in the whole body 3 then the urine ; and afterwards the folids.
THERE are three circumftances necefTary to the procefs of putrefaction, viz. moifture, heat, and the admiffion of the external air. Moillure is necefTary to foften the fibres of plants, that they may be capable of the in- teftine motion 5 for. we fee that dry flraw
Ml
will
'.-,:> . .-'••<>
Sect. V. Agriculture and Vegetation. 77
will not corrupt. Heat is likewife necef- fary, in order to excite and promote that in- ternal motion of the particles which coiifti- titutes putrefaction. As cold checks this motion, it is a great enemy to all corrup- tion. The admiffion of the external air is likewife neceflary, as no intefline motion can begin without its affiftance. Hence bodies preferved from the immediate con- tact of the external air, by being put in an exhaufted receiver, or covered over with greafe, are kept from corruption.
BESIDES drinefs, cold, and want of air, there are many other things which refift corruption. But there are no fpecies of bodies which are fo much in oppolition to it as falts in general, whether alkaline, neu- tral, or acid, but particularly the laft.
THE particular feat or fubject of corrup- tion, feems to be in the mucilaginous or oily particles ; for the more of thefe fat oily particles a body has, it corrupts, ceteris
faribtf,
<fhe Principles of Part II.
paribus, the eafier. Thus water, replete with the mucilaginous particles of an oozy fat foil, corrupts fooner than water taken from a gravelly foil.
THE natural progrefs of putrefaction in vegetables is in this way. They begin firil to heat towards the centre ; and emit a fharp acid fmell, which is owing to the acetous fermentation. As the heat advances, this fmell goes off, and is fucceeded by a very foetid one. Their colour, if it was light before, now turns dark $ and the more the putrefaction advances, the darker is always the colour. They lofe their peculiar di£- tinguifhing tafte, and gain a naufeous ca- daverous one. Their fibres, which had a certain degree of firmnefs, lofe that very foon ; there is no more cohefion betwixt the minute particles of which they were compofed, and they fall into a putrid pulp. Thefe are the general circumftances which attend putrefaction.
IF
Sect. V. Agriculture and Vegetation. 79
IF vegetables are examined chymically after putrefaction, they afford principles very different from what they did before it. Their falts, which were before fixed, are now become volatile, and their oils are much more volatile and foetid than what they were. The foetid fmell of putrefied bodies is owing to thefe volatile foetid oils flying continually off. This greater vola- tility in the falts and oils arifes from their being more attenuated than what they were.
How nature brings about thefe great changes, is difficult to fay. The moft plaufible and general theory is, that the minute particles of air, of which there is great plenty inclofed in all bodies, extrica- ting themfelves from the fibres of the ve- getable, which is now foftened by moifture, and being agitated by the heat and conti- nual alterations in the preffure of the at- mofphere, raife an inteftine motion in the
bod vi
So The Principles of Part II,
body. This inteftine motion, caufing a continual friction betwixt the falts, oils, water, and earthy particles of the plant, mull comminute them, and raife a great degree of heat. The oily particles undergo a change from this heat, and acquire a foetor j and, being joined by the air coming from the putrefied mafs, become more volatile, and affecT: the fenfe of fmelling. The inteftine motion, it is eaiy to perceive, muft take away all cohefion in the fibres and particles j and fo they fall into a pulpy fubftance. The oils and falts having a natural affinity, will unite j and fo the falts, by the natural volatility of the oil, will become volatile themfelves, from being fixed before.
THIS is a very plaufible theory, though, I muft own, liable to many objections. The heat and weight of the atmofphere, muft reach bodies preferved by the means of oil, as well as if they were not rubbed with it. We do not find thofe vegetables
which
Seel. V. Agriculture and Vegetation. 8 1
which are moft apt to putrefy, contain more air, than thofe which are lefs liable to pu- trefaction. The fixed air of vegetables is not acted upon by heat ; nor does there appear any caufe why it fhould get free. It is difficult to arrive at any degree of certainty in thefe abftrufe ipeculations. To me the firft mover feems to be that ele* mentary fire which is inclofed in all bodies, fet in motion by the external heat of the atmolphere. Hence the particles are made to recede} and the fixed air uniting, be- comes elaflic, and burfts the vefiels of the vegetable body.
THE defign and end of this procefs is more apparent, than the means which the Author of nature takes to accomplish thefe. Were vegetables to be deftroyed only by external force, by far the greateft part of them would remain untouched j and fo be an ufelefs burthen on nature. Were they to be deflroyed by an internal fermentation, as at prefentj without having their parts
G vola-
82 We Principles of Part II.
volatilized, the particles to which they muft be reduced, would be continually warned off from the foil, carried into the fea, and fo be of little ufe towards the nourifhment of other plants.
THE only proper and wife fcheme is followed. The oils and falts, from being fixed, are volatilized, carried up into the air, and defcend again to fructify the earth, which was lately robbed of them. Cor* ruption, then, is the parent of vegetation ; and could be fo in no other way than in the prefent. Though of feeming difadvan- tage in nature, as mewing it on the decay ; though highly difagreeable to the external fenfes, and often dangerous to health j yet is putrefaction of more ufe than any of the other two fermentations, as it provides for our future nourimment, and carries on that beautiful circle, which nature is command- ed, by her author and conftant fupporter, to move in.
PUTRE-
Sec~l. V. Agriculture and Vegetation. 83
PUTREFIED fubftances are all of an al- kaline nature. The alkaline fait is often indeed invifcated by the oily parts, fo that it can fcarcely efTervefce with acids. This has led fome to aflert, that putrefied fub- ilances were not alkaline ; an aflertion op- pofite to experiment. We know with what a gentle heat the volatile falts of putrefied bodies rife ; a heat incapable to form thofe falts, if they did not pre-exift ; but capable of raifing them when once formed. As pigeons dung is the ftrongefl of all dungs, for vegetable and animal fubflances are the fame when putrefied, the alkaline falts are moft obfervable in it. I have feen the fur- face of that dung covered with a white fait, which fmelt as ftrong as the volatile fait of hartmorn. Every one is fenfible of his eyes watering, when he goes into a pigeon- houfej owing to the pungent volatile falts in the air. Subftances highly putrefied ef- fervefce with acids. Reaumur, Ipeaking of the leaves of the vine, which he had fet
G 2 by
84 W* Principles of Part IL
by to putrefy : Quand elks ont cte pourrm jufyue a ce point on elks per dent leur nommes four prendre celui de terreauy elks ont fer- mente vivement et fubitement avec les acides^ que je verfes dejjut. Au lieu que Fefprit de nitre verfcfur de fuilles feches, oufur defuilks jimplement commence a pourrir^ nici produit aucune fermentation fenjible. This experiment puts the queftion beyond all doubt*
FARMERS have difcovered, by long ex- perience, that the dung of different ani- mals differs very much, as to the quantity to be uied, and the ground upon which it ought to be laid. A much fmaller quan- tity of pigeons dung muft be employed than of any other; and even that mould be laid on cold wet foil. The dung of iheep and hogs feems, by experience, to have the preference to all others. Thefe different effects depend on the different quantities of oil and volatile falts in the dung ; and thefe again on the food of the animal, on the time it flays in the inteftine
canal,
Sect. V. Agriculture and Vegetation. 85
canal, on the nature of the juices mixed with the aliment there, and on the natural heat of the body.
LET us now make fomc practical obferva- tions with regard to the management of dunghills : for this is an affair of confider- able importance, and in which farmers feem to be very ignorant.
DRY vegetables require a conliderable degree of moifture before they can be brought to putrefy. I think dunghills are generally kept too dry, as they are com- monly in this country placed on a high iituation, and are themfelves raifed to a confiderable height. A hollow fituation, which will retain the moifture, is the beft. Too much moifture is likewife bad. This may be prevented by having hollow places, with clay bottoms, at the fide of the dung- hill, into which the fuperfluous moifture may be allowed to run, and from whence it may be reftored again by pumps to the dunghill at pleafure.
G 3 BUT
86 Tfc Principles of Part II.
BUT there is yet a worfe confequence from fuch a fituation. The juices of the dunghill are diflblvable in water, and are Continually warned off by the rains which fall, Hence a great part, nay almoft the whole of the vegetable food, is loft. It is a bad advice, therefore, which the Journal Oeconomique gives, to place the dunghill on a declivity. A hollow fituation, where the bottom is clay, or where it is caufeyed, is the propereft to carry pn the procefs of corruption.
As the fun and wind exhales the volatile falts and oils, and as too much air rather retards this procefs, I mould think it very reafonable, to place the dunghill in a fituation fhadowed and furrounded by trees. There is a clofenefs and moiflure in this fituation, which will very much faypur corruption.
I fee that practical farmers advife, that the dunghill mould be covered with earth,
tQ
Sect. V. Agriculture and Vegetation. 87
to hinder the volatile particles from flying off. But how can this be done, when there are frefh additions made to the dung- hill every day ? It would indeed putrefy fooner -, but then it muft lofe the influence of the air, by which only it becomes fit nourishment for vegetables. The effects of the air on the dunghill muft be confider- able, as it is fo loofe and pervious a body. I am more inclined to agree with them in another obfervation, that the north and eaft winds mould have free accefs, efpecially in winter, to the dunghill. We mall after- wards fee, that thefe winds are found, by experience, to be more impregnated with the aereal nourifliment than the others, and particularly at that time,
A s the procefs of corruption, in the com- mon way, goes on very flowly ; and as great part of the dung which is carried out from the dunghill, is not half putrefied, and confequently not fufriciently prepared for vegetables ; it would be of ufe to quicken that procefs, if we knew of any eafy me- G 4 thod
88 'The Principles of Part II.
thod to do it. There are ferments for the putrefactive fermentation, as well as for tke vinous. Hence Stahl : Corpus in putredine exiftenS) olio a putredine liber o facillime cor- ruptlonem conciliat j quia illud ipfum, quod in motu intejlino jam pofitum eft, alter urn qui- efcensy ad talem motum tamen prodive, in eundem motum intejlinum facile abripere poteft.
ANIMAL fubftances already putrefied, fuch as ftale urine, human dung, the car- cales of animals, &c. are the proper putrid ferments. If the urine of horfes, and ftall- fed cattle, is carried into proper refervoirs, and there allowed to turn ftale, it will, if thrown on the dunghill, very much quicken the fermentation.
PUTREFIED bodies are of a very vola-* tile nature ; infomuch that if expofed to a dry hot air, they continually diminifh in bulk, until all the volatile parts being car- ried off? the remainder is found to be an
Sett. V. Agriculture and Vegetation. 89
earth moftly of the abforbent kind.' This mows, that dunghills mould not be kept too long after they are fufficiently putrefied ; and that dung mould not be expofed on the furface of the ground in hot weather, as often happens ; but immediately ploughed in, if carried out at that time. It is a£- ferted by fome fanners of obfervation, that dung, when expofed for five or fix weeks on the furface, fructifies ground more, than when it is directly ploughed in, and mixed with the foil. If this obfervation is found to be true, the winter and fpring will be the propereft feafons for expofing it. A fu- perficial ploughing after the dung is ipread, would feem to bid faireft for attaining the advantages and fhunning the difadvantages of both methods.
THE mud of ponds and ditches comes properly under the clafs of putrefied bodies, as it confifts of earth and the putrefied parts of vegetables,
SECT,
90 We Principles of Part II.
SECT. VI.
Of manures which arife from burning vege- tables.
AL L vegetables converted into afhes by the action of the fire, afford a good nourishment for vegetables, efpecially for grafs j becaufe, as their action is very fudden, it is fooner obfervable on a grafs than corn field. Chymiftry fhows, that thefe afhes confift of an indiflblvable earth, and an alkaline fait ; which latter body at- tracts acids more ftrongly than any other. Fern afhes contain the moft fait of any common vegetable which I know j the fixth part is alkaline fait. They rnuft, therefore, be the propereft for this ufe. At the alum works near Scarborough, the farmer pays 2 J. a cart-load for the refufe of the earth of thefe afhes, after almoft all the fait is extracted out of them. The refufe of the foap manufactures, and of the bleachfield, are rich manures. The
afhes
Sed. VI. Agriculture and Vegetation. 9 1
afhes of peat, which are moft ufed, afford falts equal only to the thirty-fecond part of the whole, and are the weakeft of all thofe I know.
HFRE we muft clafs the burning of the turf, or furface, which is often done to im- prove poor foil. Farmers think it ads by difpelling a four juice which land has con- traded from lying long untilled : and they chiefly prefcribe it for that fort of poqr ground ; for they all agree that it hurts rich foil. But I imagine, that the benefit arifing from it is owing to the alkaline fait arifmg frc/m burning the roots of ve^ getables : for farmers enjoin us to go no deeper than thofe roots ; and it is found, that the greater the quantity of roots, as happens in land which has been long untilled, the more benefit arifes from burning,
THERE is another manure which takes its rife from fire, and properly belongs to
this
92 *Ihe Principles of Part II.
this fe<ftion ; that is, foot. This is found, by chymical experiments, to be a compofi- tion of volatile alkaline fait, oil, and a little earth. It is remarked, that the effects of this compoft are very fudden, they being obfervable after the firft rains.
SECT. VII.
Of animal manures.
AL L animal fubftances enrich ground prodigiouily ; fuch as, blood, gar- bage, urine,. &c. becaufe they putrefy ea- iily. As we have treated of dung, we need not fpeak of thefe. But there are other animal fubftances, fuch as {havings and tips of horns, hair, filk, woollen rags, &c. which do not feem, from their firm tex- ture, to be fo capable of putrefaction. All thefe contain a great quantity of a muci- laginous and gelatinous fubftance, capable of being diffolved by water, of a fapona- ceous nature, and conlifling, as appears by chymical experiments, of falts and oils
intimately
Se<5t. VII. Agriculture and Vegetation. 93
intimately mixed, and difTolved in much water. This mucilaginous fubftance muft, then, be fit nourishment for plants.
THE action of thefe manures is com- monly attributed to their imbibing the dews, and conveying moifture to the ground. But woollen rags rather repel, from their oily nature, than attradt moifture ; and were they only fimply to conduct the moifture into the ground, linen rags would do as well : but they do not. Thefe woollen rags being much ufed in chalky grounds, which are dry, has given rife to this opinion. What thefe grounds fland moft in need of,- is a mucilaginous fubftance, which thefe rags are full of.
THE animal fhells, fuch as oyfter-fhells, periwinkles, cgckles, &c. muft be included amongft animal fubftances. Thefe are long of diflblving j but it is obferved, that in fix or feven years they make the ground fo mellow, that it muft be allowed to
ftand
94 7& Principles of Part IL
ffond a year 6r two, that it may confoli- date again, and the ferment be retrained ; clfe it is not able to fupport the corn. The reafon of this expaniion of the earth, will appear from the expanfive force of fhell-marl. Thefe different mells are a compofition of calcarious particles, fit to be converted, by the fire, into quick-lime, and of an animal oil.
WE muft here confider a body, called foell-marl, which is commonly, though im- properly, clafled with the marls. It muft be ranked amongft the mells, as it is a pu- trefied animal mell. It is a white light fubflance, with an odorous fmell, appear- ing to the eye to confift of a number of fmall mells, and generally found at the depth of a foot or two in thofe hollow grounds which have been formerly over- flowed. An animal inhabiting fuch a mell I have met with in ponds, though it is very rare. It muft have been once a very common creature in this country, and ap- pears
Seel. VII. Agriculture and Vegetation. 95
pears to have been deftroyed in moft counties at once by fome general difafter which affected it; the natural depofition of foil from thefe waters has buried it fo deep.
Exp. 30. When water is poured on this body, it fucks it in greedily, and fwells like a fpunge ; becomes very foft, but does not fall down like marl into a powder. It is by means of this quality that all fhells, whether they are laid on corrupted, or be- come fo in the foil, make ground fo very light and fpungy.
I could difcover no fait in it, by the dif- ferent trials which I made. It makes a ftrong effervefcence with acids, and requires fix times more of them to faturate it, than what any of the marls which I have yet met with do.
IT affords on diftillation, like all animal fubflances, a urinous alkaline fpirit, and an oil of the heavy kind.
WHEN
96 The Principles of Part II.
WHEN calcined in the fire, it is con- verted to quick-lime. By thefe experi- ments it does appear plainly to be a putre- fied animal fhell, eafily feparable by water, and a ftrong attra&er of acids.
PART
[97]
SECT. I.
effetfs of different fubftances with regard to vegetation.
1
E manures which I have examined, are fuch as chance di£- covered to be ufeful in vegeta- tion, and practice has continued, becaufe they can be eaiily and cheaply got. But, for what we know, there may be others, which, though not in fuch plenty as to be of ufe to the farmer, may have effects on vegetation, that may be ufeful to thofe who inquire into the nature of the vegetable food. The more they know of the effects of different bodies on plants, the greater chance they have to difcover the nourifh- ment of plants -, at leaft this is the only road. I made the following experiment with this defign.
H Exp.
98 The Principles of Part III.
Exp. 31. May 2. 1755, I took fome vir- gin earth from the fide of a fleep bank, where neither dung nor plough had ever been ; filled fome pots with it j mixed with the earth the following materials ; and fet them in the ground. Each pot contained about 61b. of earth. In each pot I plant- ed five grains of the fame barley $ and that I might be fure that each grain was proper for feed, I took none but what fell to the bottom of water. N° i. contained plain virgin earth, that I might have a Standard for the reft. N° 2. was always watered with hard water. N° 3 . had i oz. of faltpetre, and 2 oz. of oil of olives, mixed with the earth. N° 4. contained i oz. of faltpetre. N° 5. contained half an oz. of vitriolated tartar. N° 6. con- tained i oz. of flour of brimftone. N° 7. contained half an oz. of fpirit of hartf- horn. N° 8. contained 2 oz. of oil of olives. N° 9. contained fpirit of nitre, diluted with water, half an oz. N° 10.
con-
Sect. I. Agriculture and Vegetation. 99
Contained of fea-falt i oz. N° n. con- tained plain earth, and the grains fteeped for 1 6 hours in a ftrong lye of hens dung and faltpetre.
May 9. when I looked at them again, N° i. and 2. had each one plant, juft ap- pearing above ground. N° 6. had two taller than the former. N° 8. had all the five up, one of which was three fourths of an inch tall.
May 1 1. N° i. has all five up, and about Half an inch high. N° 2. has two, and as high. N° 3.4. and 5. have one each, juft appearing. N° 6. has four, three fourths of an inch tall. N° 7. has one, half an inch tall. N° 8. has five, one inch tall. N° 9. has two, juft appearing. N° 10. has none. N° u. has four. Some -of the fame grain fet in the garden-mould juft betide the pots, were three fourths of an inch high,
H 2 May
loo We Principles of Part III.
May 2 1 . five or fix days rain, and then fair weather. N° I. and 2. have five, about four inches tall. N° 3. has four, three inches tall. N° 4. has five, about two inches tall. Thofe in N° 5. are three inches tall. N° 6. has five equal to N° i. and 2. N° 7. has two, about one inch. N° 8. has fix, two and a half inches tall. N° 9. has three, above half an inch tall, and very ill coloured. N° 10. has one, half an inch tall. N° n. has five, which are the beft of all.
June i. N° 2. the beft of all, nine inches high, and of the deepeft green. N° 12. contained the next for fize and colour, and was but little inferior. N° 6. next in height, but had many withered leaves ; N° 3 . 4. and 5. about five inches tall, and of much the fame colour ; N° 7. about an inch tall, with fome of the leaves withered -, N° 8. high, but fomewhat withered ; N° 10. has three about an inch long.
June
Sect. I. Agriculture and Vegetation, i o I
June 10. N° 2. ftill bed. N° 6. almoft withered. N° 7. entirely withered. N° 9. and 10. contained poor fickly plants.
June 1 8. N° 2. ftill beft, and has nine- teen ftalks. N° 12. next, and has ten ftalks. N° i. not quite fo tall, but has thirteen ftalks. N° 3. comes next. N° 6. almoft quite gone. N° 7. none. N° 8. and 9. equal. N° 10. leaft of all.
Aug. 1 6. N° i. has feventeen ears of corn. N° 2. has nineteen. N° 3. has thir- teen. N° 4. has fifteen. N° 5. has twenty- nine. N° 8. has nine, and thofe very large. N° 9. has twenty, and thofe large. N° 10. has ftalks about a foot in length, and four or five ears, about one inch long only. N° 1 1 . has eighteen very good ones.
THUS I have related the experiment
faithfully and minutely, as becomes every
experimenter. The fads fhould always
H 3 be
IO2 'The Principles of Part III.
be related by themfelves, diftinct from all reafoning ; for we may err in the latter, but the former is truth itfelf. I mould have been glad to have repeated thefe ex- periments, efpecially with a poorer foil than what I found, by experiment, this to be. I mould have been glad to have had a greater fund of experiments to have rea- foned upon, as there is always danger of fome miftake in reafoning from a fingle experiment. But it is to be remembered, that fuch experiments can be made only once a-year, and there is no time left now to repeat and augment them. As it then ftands, I mall draw fome conclufions from
Corollary i. Virgin earth, taken up within a foot of the furface, and from a bank which had a north afpecl:, contains in itfelf the prin- ciples of vegetation in great plenty. Such earth is ufed as a manure by farmers ; and they obferve, that virgin foil wilt fructify earth much richer in appearance than itfelf.
Cor.
Sect. I. Agriculture and Vegetation. 103
Cor. 2. Grain appears to grow better, that it has been fteeped in dung and falt- petre. It is a fadt long ago bbferved, that grain vegetates flronger, quicker, and is lefs fubjecl to blight and mildew, if it has been fteeped in liquors which contain fait and oil, fuch as fea-water, ftale urine, &c. This is eafily accounted for. It is certainly of great moment, with what the vefTels of the feed are at firfl filled, whether with watery or with rich juices. This is one great reafon that makes a dry feed-time fb ufeful : for if the ground is dry, the juices which the feed imbibes, are rich and nu- tritious ; whereas in rainy weather, thefe juices are diluted with too much rain, and the tender plant is weakened. In medica- ting grains, we fill their veflels with plenty of falts and oils, and give them vigour to fend out many roots, upon which the nou- rimment of plants depends. The way to make a ftrong man, is to nourifh the child with fuitable food.
H 4 Cor.
1 04 cfke Principles of Part III.
Cor. 3. Hard water appears to afford a ftrong nourishment for plants. This is very oppofite to the common received opinion : for gardeners never ufe it, when they can get foft water •> and if they fufpect any hardnefs, endeavour to foften it as much as they can, by letting it ftand expofed for fome time to the heat of the fun. In this, however, they are miftaken. This expo- fition may make water harder j but can never foften water which is confiderably hard. The hardnefs of this water which I ufed, and indeed of all hard waters * which I have met with, was difcovered, by experiments, to be owing to the acid of nitre, joined to an abforbent earthy bafe. The bafe in this water was a calcarious earth $ in moft hard waters it is only an abforbent.
Cor. 4. Oil of olives, in the proportion
* Vid, Experiments on bleaching, fe&. on hard waters.
Of
Sect. I. Agriculture and Vegetation. 105
of i oz. to 3lb. of earth, appeared to have very good effects at firftj but thefe afterwards declined. The ears were good, though not many. Was the oil in too great quantity? Was it not fufficiently attenuated by the falts in the earth; and, by that means, did it not block up the mouths of the radical veflels ? Had it not fufficient time to incorporate with the earth ? Thefe are queftions which I cannot refolve.
Cor. 5. It appears, that faltpetre, in the proportion of i oz, to 6 Ib. of earth, rather retarded than promoted vegetation. This indeed furprifed me, as I generally believed nitre to be of a very fruitful nature ; nay, the very caufe of fertility. It does not feem to have been employed in too great quantity neither. Its great reputation for fertility would make one cautious in doubting that efFecl:, without a fufficient number of experiments to fupport that opinion.
Cor.
io6 <Tbe Principles of Part III.
Cor. 6. The vegetative effects of nitre does not feem to have been increafed by the addition of twice its quantity of oil of olives. The oil of olives feems to have fucceeded better with the addition of the nitre than without it. The falts would at- tenuate the oil, and help it to enter the veffels of the plant more eafily.
Cor. 7. Vitriolated tartan which is a compofition of the acid of vitriol and an alkaline fait, feems to promote vegetation very ftrongly. A gentleman wanted to de- ftroy fome rank grafs in his court, and was advifed to iprinkle it with the oil of vitriol, as the greateft enemy to vegetation. He did fo 5 but, to his great furprife, the grafs came up much flronger than before.
Cor. 8. Sea-falt, in the proportion of I oz. to 6 lb. of earth, appears to be an enemy to vegetation. Moft farmers comr- mend it as a good manure, though there
are
Sett. I. Agriculture and Vegetation. 107
are fome who doubt of its good effects. Perhaps in a fmaller quantity, its effects may be more beneficial ; efpecially if it contains the bittern, which is a competi- tion of the vitriolic acid, and an abforbent bafe*, and a bituminous oil, both of which muft be affiftants of vegetation. The fait which I ufed being table-falt, was in a great meafure freed from thefe.
Cor. 9. The acid of nitre feems to have retarded vegetation at firft; perhaps from its being not fufficiently united to the ab- forbent particles of the foil. But at laft it feems to have promoted the growth of the plants coniiderably.
Cor. 10. Spirit of hartmorn, which is a volatile fait diluted with water, feems to have poifoned the young plants.
Cor. n. Flowers of brimftone, i oz. to 6 Ib. of earth, appears to have promoted vegetation greatly at firft 5 but in a month's
time
io8 Vbe Principles of Part III.
time to have deftroyed the plants like a poifon. This fubftance is often fprinkled on turnip-feed before it is fowed; and it is thought by farmers to amft their growth, and to keep the flies from the leaves. Was too great a quantity of it-ufed in this ex- periment ? Plants, therefore, have not only their food, but their poifon. Quter. Will the artificial fulphur, which arifes from the combuftion of many plants in a particular way, and which is to be found in great plenty in kelp-afhes, in the foap-ames, and in many of the afhes ufed in the bleach- field, have the fame bad effects as natural fulphur ?
AFTER the laft experiment was made, there appeared to me a confiderable diffe- rence betwixt the method by which it was carried on, and the courfe which nature follows in fuch operations. I mixed the materials, whofe effects on vegetation I wanted to difcover, all at once with the earth: but in a natural way, the fructifying
prin-
Sect. I. Agriculture and Vegetation. 109
principles muft be beftowed on it by gentle degrees, and in very fmall quantities. Earth, indeed, which has lain for fome time fal- lowed, and is therefore well ftored with the feeds of vegetation, is much in the fame ftate with the earth of my experiments, though not fo much faturated with the nutritive principles, as mine was with the different materials. Befides, the former is conftantly receiving frem fupplies. That I might approach nearer to the courfe of nature, and fupply materials according to the growth of the plants, the following ex- periments were made.
Exp. 32. Six pots were filled with poor, light, virgin earth. Each pot contained 5 Ib. and 5 grains of heavy barley. N° i . had no mixture. N° 2. was watered with I dr. of faltpetre dirTolved in 3 oz. of water. N° 3. with the fame quantity of fea-falt. N°. 4. with the fame of Epfom fait, which is compofed of the acid of vitriol, and the earth, called magnefm alba. N° 5. with 2
dr.
no The Principles of Part III.
dr. of the following compofition diluted in water. Half an oz. of quick-lime was feturated with weak fpirit of nitre, which produces a very cauftic liquor. N° 6. with 2 dr. of the former mixture, having half its quantity of oil of olives mixed with it. This compofition appeared to me to ap- proach near to the natural vegetable food. All the feeds were fown June 16. 1756, except N° 6. which was not till the ipth of June. I planted fome of the fame feeds in the garden-mould befide the pots.
"June 23. N° i. has one plant, half an inch high. N° 2. has one, an inch tall* and another, juft appearing. N° 3. none. N° 4. has four, two of which are one inch tall. N° 5. none. N° 6. has three, one inch tall.
June 27. N° i. has four, two and an half inches high. N° 2. has four. N° 3. has two, the talleft is an inch high. N° 4. has five, two inches. N° 5, none. N° 6.
has
Se£t. I. Agriculture and Vegetation* in
has four as tall as N° 4. Thofe .in the rich garden foil were three and an half inches tall.
July 4. N° 2. taller and greener thim N° i. N° 4. and 6. equal to N° i.
July 10. N° 2. beft. N° 6. next. No. 4. next. N° i. and 3. follow. N° 5. has one, three inches high.
July 15. N° i. four of the five plants have yellow withered leaves. N° 2. and 6. deepeft coloured and talleft. N° 3. and 4. equal. N° 5. has one weak plant, about fix inches high. The weather has been hot for ten days. Added to N° 2. 3. and 4. i dr. more of each of their falts, and to N° 5. and 6. the fame quantities of the fame mixtures.
July 24. has rained five days. N° 2. and 6. about fifteen inches tall, and much better than the reft; the latter rather beft.
NQ
112 lie Principles of Part III.
N° 4. next beft, and twelve inches tall. N° 3. next, and nine inches. N° j. next. N° 5. has one, about twelve inches. Thofe in the garden foil near two feet, and have fent up many more (talks.
Auguft 19. The laft fortnight cold rainy weather, with eafterly winds. N° 6. is the talleft, of the deepeft green colour, and therefore the beft. The reft as formerly. Added to each the fame quantity of falts and mixtures as before.
September i . Has been good warm wea- ther. The plants as before.
September 26. N° i'. had ten ears, the largeft of which carried twenty grains. N° 2. has eleven, the largeft of which had twenty-four grains. N° 3. worfe than N° i. N° 4. has thirteen ears, the largeft of which carries twenty grains. N° 5. has but one ear -, and that is not fo ripe, and has fmaller grains than the reft. N° 6.
has
Seel. I. Agriculture and Vegetation. 1 1 3
has fixteen ears, many of which carry twenty-four grains, and thofe larger than any of the reft. It has one double ear, which has forty grains. Many of the ears in the garden foil have thirty-two grains.
LET us now draw fome corollaries from this experiment.
Cor. i. Sea-falt added in fmall quantities, and by gentle degrees, to a poor foil, feems again to be rather hurtful than beneficial to it. What efFeft it would have on a foil full of oleaginous particles, appears not from this experiment,
Cor. 2. Saltpetre managed the fame way, promotes vegetation confiderably, and ap- pears to have made the foil capable of pro- ducing a fourth more.
Cor. 3 . Epfbm fait applied the fame way, is pretty nearly equal in its nutritive power to faltpetre. The foregoing experiment
I taught
H4 *fhe Principles of Part III.
taught me the good effects of the acid of vitriol faturated with an alkaline fait; the prefent teaches me, that the fame acid fa- turated with a particular abforbent earth, promotes fertility. Hence I concluded, in part 2. feet. ,3. that marl added to the fame acid, after the poifonous chalybeate particles were feparated from it, would ra- ther be of fervice than difiervice to the foil.
Cor. 4. Quick-lime, faturated with fpirit of nitre, added in fmall quantities, and well diluted with water, appears to have hurt the vegetative power of the foil. Was it ufed in too great quantity ? or did it not meet with what is as necefTary to vegetation as itfelf, a due proportion of oleaginous par- ticles, which nature always fupplies in pro- portion as me fupplies the falls ? The latter feems to have been the cafe, from the fol- lowing corollary.
Cor,
Sect. I. Agriculture and Vegetation. 115
Cor. 5. The former liquor, with half its quantity of oil of olives added to it, and (halted well together, appears to have en- riched the foil moft, and to have nearly doubled its fertility.
Cor. 6. None of our admixtures was able to bring the poor light foil to the fame fer- tility with the rich garden mould. And no wonder. There the falts and oils are highly attenuated, duly proportioned, and well mixed, by length of time ; and, con- fequently, fitted to enter the fmall veflels of the roots. Befides, that foil, by the mix- ture of putrefcent matter, is in a conftant ftate of fermentation, becomes eafily pene- trable, and offers a larger field for the roots of plants to feed on.
A s lime never ads on the foil till it be- comes effete, I was willing to fee its effects when faturated in that flate with the acid of nitre; although experiments feem to I 2 fhow,
1 1 6 The Principles of Part III.
mow, that the product is much of the fame nature. Half an oz. of old lime wall, was therefore faturated with the fpirit of nitre.
Exp. 33. July 15, 1756, two pots were filled with the fame earth as ufed in the former experiment, and in the fame quan- tity. Three grains of barley were fown in each pot. N° I. contained plain earth- N° 2. was watered with i dr. of the folu- tion well diluted.
July 25. N° i. has three plants, one inch in height. N° 2. has one, the fame height.
^ 19. N° 2. has only onej but that is of a deeper green than any in N° i. Added to N° 2. the fame quantity of mix- ture as before.
Sept. 26. N° 2. of a deeper green, has more after-moots, and a longer ear than any in N° i.
Cor.
Sect. I. Agriculture and Vegetation. 117
Cor. I can hardly fay whether the foil was the better or the worfe for the mixture : for, on one hand, only one of the feeds took effect y and on the other, that plant was in a more thriving ftate than any plant in the plain earth. This, however, appears plain, that it had not the bad effects of the ipirit of nitre and quick-lime in the former expe- riment. Was this owing to the lime being quick in the former, and effete in the latter cafe ? or to a fmaller quantity of the mix- ture being ufed ? I raiher incline to the latter opinion, as the mixtures appear to be fimilar by experiment.
THAT I might difcover the effects of the fame folution on rich garden mould,
Exp. 34. July 14, 1756, I filled two pots with 5 Ib. each of that foil j fowed four grains of barley in each, and watered N° i . with the fame quantity of the fame folution uied in the foregoing experiment. July 20. three plants have appeared in each 13 pot;
n8 The Principles of Part III.
pot; thofe in N° 2. a degree taller than thofe in Na I. July 27. the plants in both pots equal. Aug. 13. the plants in N° i. are r,ather taller than thofe in N° 2. : but none of them thrive well ; either becaufe they were late fown, or becaufe they were in a corner where two tall hedges met, and therefore wanted air. I removed the pots to a more open place. Sept. I. N° I. has one taller, and of a deeper green, than N° 2. The plants have grown fafter than before. Sept. 30. the plants are come to no per- fection.
Cor. i. The plants in the two laft expe- riments did not vegetate near fo quickly in the fame time, as thofe of the preceding experiment had done. Has not the ipring, from fome particular caufes which operate at that time, a peculiar vegetative power, which the fummer poffeffes not in fo great a degree ? So it appeared to me, although the fummer was cold and rainy, like our fprings, and the foil in the latter experi- ment
Sect I. Agriculture and Vegetation. 119
ment very rich, and in the former taken from the fame place that the earth of the foregoing was.
Cor. 2. Plants feem to ftand in need of a conftant application of free air to their furfaces. All trees in thickets ftretch out their branches either laterally or longitu- dinally, where they can have moft air. Does this air act only on their furface ? or does it enter the vefTels of the plant ? If the latter, is not an impetus from the air in motion ne- ceffary in order to its entrance, as the mere preflure of the air is always the fame in fimilar altitudes ?
Cor. 3 . The plants feem neither to have been much better, nor much worfe, for the addition of the faline mixture.
Exp. 35. May 25, 1758, I fovved fome
barley in 4 different pots, filled with the
fame poor earth. N° i, contains the pure
earth. N° 2. the fame earth frequently
I 4 watered
120 The Principles of Part III.
watered with a folution of that particular fait found flicking on the plaiftered walls of boghoufes, &c. It got altogether i dr. of this fait. N° 3. fame earth watered in the fame way with the fame quantity of crude tartar, which was the only eflential fait that I could get at the time. N° 4. the fame earth treated the fame way with the fame quantity of foluble tartar, which is the former acid fait neutralized with an alkaline fait.
June 10. All pretty equal. July 25. N° i. has two ears, and the worft of all. N° 2. has feven, all larger. N° 3. has five, very good. N° 4. has three.
Angujl 8. N° i. has nine. N° 2. has four- teen. N° 3. has nine. N° 4. has fifteen.
22. N° 4. has the heavieft ears, and ftrongeft ftraw. N° 2. is next to it. N° 3. is better than N° i.
Cor.
Sect. I. Agriculture and Vegetation* 121
Cor. i. The aereal nitre promotes vege- tation very much. This fait we elfewhere prove to be the foflil alkali.
Cor. 2. The eflential fait of rhenifh wine promoted vegetation a little. The fame fait neutralized, had very ftrong effects on the growth of plants.
THAT I might difcover the natural ef- fects of rain-water,
Exp. 36. May 23, 1758, I took two pots filled with poor earth, {owed fome barley in each, and placed them near the window of a green-houfe, fo that they might get air, but no rain. NQ I. was conflantly watered with fpring- water.' N0 2. with the fame quantity of rain-water.
June 10. The plants watered with rain- water, feem the beft ; but thofe of both pots appeared fickly for want of a fufficient quantity of air.
Principles of Part III.
Aug. 2. The rain-water appears ftill beft. 22. I cannot fay which is beft, as they are both fo fickly.
THESE are all the experiments which I have made with regard to the effeds of different bodies on vegetation. This field has not been cultivated with that attention which the merit and importance of the fub- jedl requires. It is indeed extenfive, as it takes in the operations of all bodies which can be either dirTolved or attenuated, fo as to enter the veffels of plants. But it is only from a number and variety of trials made in it, that we can expecl to fee a juft theory of vegetation arife. I could wifh, before I attempt that fubjecl, to be pofleffed of a greater number, and thofe oftener repeated, that my conclufions might have been more general and more certain. They were fuch as appeared to me to refult naturally from the experiment. How far they are to claim aflent, I have left in every one's power to judge. SECT.
Se£t II. Agriculture and Vegetation. 123
SECT. II.
Of the food of vegetables.
WE now come to treat of that impor- tant queftion, What is the food or nourifhment of plants ? a queftion which has been much handled, but not fufficient- ly afceftained yet. It has even been made a queftion, Whether each plant has not its peculiar and proper food, which it chufes amongft the reft, from fome elective power inherent in its roots ?
THOSE who take this fide of the queftion, aflert, that the advantage arifing from the change of fpecies is a certain proof of this ; for if the fame nourishment ferved all grains, the fame grain would thrive in the fame ground, as well as another j that al- though wheat will not fucceed in the fame ground for two years fuccefiively, yet it will bear another grain very well; and that the different nature and properties of
vege-
124 The Principles of Part III.
vegetable juices are a flrong proof on their fide.
THOSE who affert, that all vegetables feed on the fame food, fupport their opi- nion by the following arguments. The longer ground is kept in tillage, though it bears grain of different fpecies, the worfe it becomes : but this would not happen, if plants took different particles from the foil : That all fort of weeds ftarve corn, by taking part of the fame nourishment : That fallowing ground would be an ufelefs prac- tice, fince there is fuch a diverfity of fpe- cies: That it would be in vain for plants to have a tafte, fmce they have no local motion : That change of fpecies fucceeds, not becaufe plants take only their own food, but becaufe fome loofen, while others bind the ground j fome roots go deep into the ground, while others keep about the furface : That it is true, wheat will not fuc- ceed in the fame ground two years fuccef- fively, becaufe it requires more food than
that
Se6t II. Agriculture and Vegetation. 125
that ground can afford, although there is fufficient nourishment left for other grains ; and there would be no time left to plough the ground, as wheat is fown in the har- veft: and, That the difference of vege- table juices depends not on the difference of food, but on the particular ftruclure of the veffels of plants.
THE latter opinion muft appear to every one to be nearer the truth than the former : nearer the truth, I fay, becaufe the advo- cates for it feem to think, that one fort of food ferves all vegetables. There I differ from them. We faw, by the experiments in the lail fection, that the fait of hard water, Epfom fait, and the vitriolated tar- tar, falts very different from one another, nourifhed vegetables of the fame fpecies; and therefore the food is not of one kind. We know that fome trees contain the acid of vitriol, becaufe with their charcoal we can make a fulphur. We know, likewife, that fome plants contain a nitrous fait,
while
126 The Principles of Part III.
while others one like fea-falt. Some vege-^ tables require a greater proportion of wa- tery parts, and fome a fmaller. The food of vegetables, then, is not all of the fame kind. J-u- A,, /«.&Arfe M^LM
M
? HALES maintained, that all things were made from water.
HE L MO NT was of this opinion, and fupported it by an experiment known to every perfon. He planted a willow, weigh- ing 5lb. in a pot filled with dry earth. The earth he watered with rain-water. In five years the willow, not computing the leaves which had fallen off, weighed 1 64 Ib. ; but the earth had loft nothing. That elementary water is the food of ve- getables, is a conclufion too ftrong from this experiment. It only mows, that water contains particles which are capable of nou- rifhing plants. We have fhown, that fnow and rain-water contain earth, oil, and as they fvveep the air, muft contain fuch falts as are in it too. SOME
-•
Sect I. Agriculture and Vegetation. 12 7
SOME modern philofophical chymifts, fuch as MeiT. El/er and Euler, are of opi- nion, that water is the nourifhment of plants. The latter found that onions and fome branches grew in diftilled water. But the experiment does not convince me, for diflilled water, as well as rain-water, con- tains falts and oils. He owns in the fame paper, that the diftilled water, expofed to the fun, recovered its falts, oils, and earth. It will, then, recover the fame principles when the plants grow in it. It is not ne- ceflary here to enter into that nice difcu£ fion, whether water receives thefe princi- ples from the air, which I think moil pro- bable, or is converted into them, which is his opinion j it is fufficient for my pur- pofe to fhow, that thefe principles enter the veffels of the plants along with the water. As I know no experiment that eftablifhes this opinion, it appears to ftand in oppofition to all my experiments : for fome falts have ftrong vegetative powers j
but
128 fbe Principles of Part III.
but thefe do not arife from attracting and retaining moifture, as thefe powers do not appear to be in proportion to that quality.
OTHERS think, that the more terrene particles are thofe which nourifh plants. Of this opinion is the famous Tidl; be- caufe, fays he, earth augments them ; and whatfoever augments them, muft be their food. Dung, and other manures, 'act only by fermenting, and fo attenuating the foil ; and are of no more ufe, than, as a knife, to divide their food. But earth alone could never do, without fome more active prin- ciples. Mad Tutt been a chymift, he would have known, that mere earth makes but a fmall part of all plants. Soil may certainly be too loofe. To earth already fufficiently attenuated, manures would do no fervice. Whence the falts and oils of plants? Thefe are objections which the favourers of his fyftern never can anfwer.
OTHERS
Setf. II. Agriculture and Vegetation. 129
OTHERS, feeing the neceffity of the air to all plants, and obferving that plants im- bibe a great deal during the night, as Dr. Hales 's experiments fufficiently mow, affert, that the foil only gives them fupport, but air nourimment. To this the anfwer is fhort, That plants thriving better in fome foils than in others, and in proportion as thefe foils are manured, fhows the ground to be the principal pafture of plants ; the air being the fame in grounds adjoining to one another.
THE author of the Hijlolre Phyfique de- duces all plants from certain fimilar orga- nifed parts, which he fuppofes flying up and down the air in great plenty, and which attach themfelves, in fome unknown way, each to its own tribe. If this were the cafe, dung made of plants of the fame fpecies, would fucceed beftj which is net fo. I lhall allow this unphilofophical opi-
K nion
130 tte Principles of Part III.
nion to fall of itfelf, as it mutt naturally do, when unfupported by experiments.
OTHERS attribute vegetation to falts of different kinds. But whence they come, and of what nature they are, we have only their own affertion.
IT is the common fate, in all difputed points, that each attaches himfelf to one fide, without allowing the other any fhare of truth. I have found by experience, that each fide has generally fome truth in itj that mankind err by extending that parti- cular truth to a general one j and that the real truth is generally made up of fome- what taken from each opinion. The rea- foners on agriculture have failed, becaufe they afierted, that plants were fed either by air, water, earth, or fait. I join, in fome meafure, with all thefe ; and aflert, that plants are nourished by thefe bodies, united with two others, oil and fire in a fixed ftate, Thefe fix principles joined together,
4- >£ 'm
<fa n, t,j tirtdjtrt '. £ •
JVL- a Jtefat ft 'fa^*kw*3~!&*& 176
Sect. II. Agriculture and Vegetation. 131
in my opinion, conftitute the vegetable nou- rifhment. *
THIS eafily appears, when we confider, i . That feveral kinds of nourishment, fuch as leather, hair, horn-fhavings, rags, and all vegetables, and vegetable juices, in an intire ftate, prove proper food for vegetables. 2. That all vegetables and vegetable juices afford thofe very principles, and no other, by all the chymical experiments which have yet been made on them with or without fire. More arguments could be brought; but thefe two I think conclufive.
AIR active and fixed is to be had every where, if we are not at much pains to ex- clude it. Elementary fire is to be found in all bodies. Earth may be fupplied by any foil managed with proper care. Water drops from the clouds. Oil is a natural principle of all earth, defcends with the rains and fnows, and is communicated to the ground by all the vegetable and animal K 2 manures^
132 The Principles of Part III.
manures, in a found or putrid ftate, as our experiments have fhewn. But whence the fait, the moft adive, and, therefore, moft neceffary principle of all ? We have not as yet difcovered any in rich foil, nor in the manures moft ufed, rj/#. lime, marl, mells, chalk, &c. This is an important queftion ; opens up the action of almoft all manures, and of rich foils ; mows wherein the effect of the air confifts j and, therefore, deferves a particular difcuffion.
THE preceding experiments have mown, that all fertile foils, and all manures, ex- cept thofe already converted into a mucila- ginous nature, confift of particles, .which, in part, or all together, attract acids. Dung, the afhes of vegetables, burnt earth, contain fuch particles j lime, marl, animal (hells, chalk, &c. are wholly of this nature. Thefe then muft attract and retain all acids, when they come within the fphere of their attra&ion. If the air, to which the foil is continually expofed, contains any
acids,
Seel. II. Agriculture and Vegetation. 133
acids, thefe bodies will draw it out, and be converted to a neutral faline fubftance, en- joying the properties of fait, fuch as folu- bility in water, difTolving oils, and render- ing them mifcible with water. Nothing, then, remains to be proved, in order to the converfion of thefe manures into a fait, but that the air contains an acid fait.
THIS has been the opinion of the greateft chymifts, not from theory alone, but be- caufe they difcovered, that alkaline falts, when expofed to the air, were converted into neutral onesj and that metals, fuch as tin, copper, and lead, were corroded, and converted to a fait. Whether there is fuch a fait, and what its nature, will be beft afcertained and illuftrated, by confider- ing the manufacture of nitre. This procefs ' too will (how the operation of the different manures, as thefe are the very materials ufed in this manufacture.
K 7 THE
• * w
134 lie Principles of Part III.
THE mofl common materials out of which nitre is made, and, therefore, called the matrix of nitre, are the rubbifh and earth of old houfes, and efpecially of dove- cotes, ftables, and church-ides ; particular fat earths ; the afhes of burnt vegetables ; putrefied animal or vegetable fubftances $ and fome particular kinds of ftones. Thefe materials are expofed to the air for fome months, particularly the winter months j for, during that time, nitre is generated in the greateft plenty. The place where the materials are expofed, mould be acceffible to the air and winds, but not to the rays of the fun, or to the rains. The air is ne- ceffary, as it generates the nitre j but the fun is deftructive, as it exhales it. The rains are prejudicial, becaufe they warn it away when made. Drought is as deftrudive, as that exhales the faline parts after they are formed, and hinders the fermentation, ne- cefTary to draw the nitre, and to open the matrix to receive it. It is obierved, that the north winds are particularly productive
pf
Sect. Hf Agriculture and Vegetation. 135
of the fait. In the Indies, from which we have moft of our nitre, they expofe earth of a particular kind, mixed with putrefied vegetables, to the air, and from that extract the nitre. Tourncfort tells us, in his travels, vol. 2. p. 289. "In our converfation in " the caravanfera of Erzeron, we learned " from thofe of the caravan of Wan> a " Turkifh town on the frontiers of Perjia^ " that they carefully lay up in heaps the " dirt of the great roads, which are fre- <c quented by caravans of camels. This " earth they warn, and every year get out " of it about i oo quintals of nitre,"
IN the manufactory of nitre at Paris, where there is much made, they expofe the rubbim of old houfes, mixed with the ames of burnt vegetables, to the influence of the air for fome months, and moiften it often with ftale urine j and from thofe materials extract their nitre. After all the nitre is got out of them, they are as fit as before to form more; and are again thrown on {he K 4 heap,
136 The Principles of Part III.
heap. This fact fhows, that this fait is not the natural fait of the earth, but formed by its expofition to the air. After thefe earths have been expofed a fufficient time to the air, they are put into different cafks, and water poured over them, to lixiviate or diffolve the falts. The materials muft be frequently ftirred about in the water, that it may diffolve the falts. After the water is fufficiently impregnated with the falts, they draw it off, and add to it fome quick-lime, and the aihes of vegetables or alkaline falts, if it has not already got enough of them ; the former to feparate the oil from the fait, the latter to give it a fixed alkaline bafe in- flead of an earthy one. They add alkaline falts, as long as their addition makes the liquor take a milky appearance, and yield a precipitation. When no more precipitation happens, then they decant the liquor, and boil it up.
LET us now inquire into the origin of nitre. There are various opinions about
this
Sect. II Agriculture and Vegetation. 137
this fait -y nor are chymifts yet agreed about its birth. Some alledge it is attra&ed, as we fee it, from the air j others, that it is produced from the animals and vegetables, or their juices mixed with the nitrous earth, and putrefying there: others, that it is formed from the vitriolic acid, joining to the phlogifton, or inflammable matter of thefe lubftances : and others, that the acid of nitre is a different acid from the former, and attracted by thefe bodies, which are its proper matrix. Let us examine thefe dif- ferent opinions.
SALTPETRE is an artificial body, as none of it has ever yet been found in the bowels of the earth. Some authors, on this ac- count, thought that the nitre was altoge- ther attracted from the air by the mate- rials expofed to it. But this opinion is ap- parently falfe, as no nitre can be got from thofe materials before an alkaline fait is added to them. The acid, indeed, does in thefe materials, as I mail after- wards
138 *Tbe Principles of Pgrt III.
wards (hew 5 but the alkaline bafe rnuft be given it by art, before any nitre will cryf- tallife. Befides, nitre is not of itfelf a vola- tile body ; and, therefore, cannot float in the air. The aereaj nitre, which is got flicking to old walls, is a very different fub- flance from the nitre we are juft now treating of. It has very different properties, fuch as effervefcing with all acids, and a urinous tafte,
LEMERTy in a paper in the Mem. de Tacad. des fciences pour fannee 1717, main-t tains an opinion peculiar, I believe, to him- felf, That the nitre which is generated, arifes from the animal and vegetable fub- flances which are ufed to colled it. The arguments which he makes ufe of to fup- port his opinion, are, indeed, few and weak. I think his chief one is, that he has extracted a nitrous fait from fome vege- tables. It is true, that fome of them do contain, in their natural flate, an inflam- mable fait, which appears to have many of
the
Se£t.II. Agriculture and Vegetation. 139
the properties of nitre. This is the cafe with the carduus benedictus, wild cucum-r ber, and pellitory. Bcildue, in 1734, has a paper in the academy of fciences, where he fays, that he extracted real nitre from a decoction of bourache, efpecially when he added fome quick-lime to it, to fix the oily particles the better, that the falts might cryftallife. He fays, that a mould which formed itfelf on this decoction, after it had been kept for fome time, burnt lilce oil and nitre. But all this is no proof, J:hat the nitre comes from the vegetables ufed jn the making nitre j for all kind of vege- tables do equally well, even thofe which contain a vitriolic fait. Befides no fixed fait is ever got from putrefied vegetables, or from any animal fubftance, which Lemery feems to have forgot. It is furprifing, that a chymift fhould fall into fo great an error. Thefe vegetables and animal fubftances; act, as we mall foon fee, in a very different: way, by affording an abforbent earth, and yolatile alkaline fait, and fo increafing the
matri?c
140 The Principles of Part III.
matrix to extract the acid from the air ; and by keeping the matrix open to admit the air, by a continual fermentation carried on in the body expofed.
TH E third opinion, which almoft all chymifts follow, is, That the alkaline vola- tile falts, produced by the fermentation of corrupted bodies, animal or vegetable, and the abforbent terreftrial particles, which are ufed as the matrix to make nitre, at- tract from the air, which is plentifully ftored with it, the acidum vagu/n, or vi- triolic acid j which joining with the oil of the matrix, flored with it, becomes the acid of nitre. This univerfal acid, Hom- lerg makes the origin of the nitrous and {he marine acid : for, added to an inflam- mable matter, it becomes the nitrous acid ; to an arfenical matter, it becomes the marine acid. The arguments ufed in fa- vour of this opinion are, i . That putrefied animal fubftances are employed in the for- mation of nitre, and, therefore, the oil
mull:
Sedt. II. Agriculture and Vegetation. 141
muft join with the vitriolic acid. But this conclufion will not be allowed as a juft one, feeing thefe putrefied fubftances may have other ufes, as we will fliow. It will pre- fently appear, that nitre may be got with- out any oily matter. 2. The fpirit of nitre has a reddiih colour, which they fay is an argument, that it contains an inflam- mable fubftance, and it is that fubflance which gives the colour to all bodies. But we know many bodies which are coloured, although we have never yet been able to mew that they contained an qil ; therefore this may not. 3. The inflammability of nitre, which it owes to its acid, proves, they fay, that it contains an oily principle, which is the only inflammable body that we know. To this opinion the anfwer is plain, That nitre of itfelf is not inflam- mable, unlefs it meets with an inflam- mable body. This argument becomes ra- ther an objection againft this opinion, as it may be faid, that nitre inflames with all bodies which contain an oil ; and as it is
not
142 <fhe Principles of Part III.
not inflammable of itfelf, therefore it does not contain an inflammable fubftance.
THIS leads me to the laft opinion, That the nitrous acid exifts in the air, and is at- tracted from it. This opinion, though fcarcely maintained by any chymift, to me appears to be the ftrongeft, though ftill liable to fome objections. The firft argu- ment for it is, That alkaline fait and cal- carious bodies of themfelves, without a mixture of any vegetable or animal matter, will produce nitre ; as we find by an expe- riment of Stably in which he got nitre by expofing alkaline falts to the air. I have got a nitrous fait from the lime taken out of park-walls. The fecond is, That it is actually found exifting in nature. Many mineral waters contain a nitrous fait, as appears by the experiments of Du C/osy performed before the academy of fciences at Pan's. I have difcovered that the nitrous acid exifts in all hard waters* ; and that
* Vid. Experiments on bleaching.
all
Se£t. II. Agriculture and Vegetation. 143
all pit-well waters are hard, and contain a nitrous acid joined to an abforbent bafe ; which imperfect -fait, by the addition of an alkaline fait alone, can be converted into real nitre. Thirdly, by boiling hard water, or expofing it to a great degree of heat, the nitrous acid is really volatilifed, and the abforbent earth falls to the bottom. This proves, that the nitrous acid is vola- tile, and exifts in the air. The fpiritus nltri fumam is continually evaporating in the air. Thefe experiments prove, I think, beyond all doubt, that the nitrous acid exifts in the air, diftinft from the vitriolic acid. This nitrous acid appears to be the fructifying principle which we formely di£- covered in the air.
THIS point being fettled, let us now ac- count for the different changes brought about in the making of nitre. All earths are not fit for this purpofe ; only fuch as are attra<5lers of acids, or abforbent earths, lime, marl, and the other abforbents -,
or
1 44 The Prwcifi/es of Part III.
or putrefied vegetables and animals, which afford an abforbent earth, and likewife a volatile fait. Almoft all earths have more or lefs of abforbent particles in their com- pofition. Thefe abforbent earths catch the nitrous acid, as it paffes by them with the air, or fix and collect it as it arifes from the inner parts of the earth : for I am not fure but it may be got likewife in that way ; at leaft it does not feem to rife very high from the ground. Mariot's experi- ment is a proof of this. He expofed the matrix of nitre for two years on a houfe- top, and could get no nitre from it -, but got it from the fame matrix kept in a cellar.
THE mixture of urine, and of putrefy- ing vegetable and animal fubftances, will be of confiderable ufe in carrying on an inteftine motion in the mafs of earth, keep- ing .it open, and allowing the influence of the air to penetrate deeper into the body. If there was no fuch putrefcent body mix- ed
Sect. II. Agriculture and Vegetation. 145
ed with it, the mafs would cohere too firmly together, and its furface would only act ; whereas now the whole body acts. It is in this way that I imagine the animal and vegetable fubftances chiefly operate, and not by entering into the compofition of the nitre, as moft chymifls affert; be- caufe nitre may be made by expofing alka- line falls alone to the air ; for alkaline falts attract acids, and are fo loofe as to fland in need of no fermentation to open their texture. The north wind is particularly proper for the generation of nitre, be- caufe that wind mufl bring more of the nitrous acid along with it. That the cold we feel from that wind, is chiefly owing to a greater quantity of this acid, I think is probable, though not demonftrable. The winter months are particularly good, as the north wind blows more in that feafon, than in any other, and as there is lefs heat to exhale the nitre during the opera* tion.
146 The Principles of Part lit
I N this way the matrix of nitre is im- pregnated with the acid of nitre. Let us now fee what this matrix at pfefent con- tains. We have the analyfis of it by Petit in the academy of fciences. He took 50!. of old plaifter, and diflblved it in 72 Ib. of water. This gave a pungent bitter reddifh liquor, which was in weight to common water as 32 to 31. When the water was boiled into a liquid extract, for it would not harden, it ibon attracted the moifture, and turned liquid again. It turned blue paper red; mewed no effer- vefcence with fp. mtr. or Jp. faL mar. j and when mixed with the former, diflblved leaf gold. OI. vitr. made a violent fer- mentation and precipitation with it. OL tart. p. d. did not eafily mix with it ; but when ftirred, produced a coagulum like butter, and gave a ftrong urinous fmell. Jf fublimate was mixed with the oL farf. no urinous fmell was felt. This coagulum was owing to a feparation and precipita- tion
Seel. II. Agriculture and Vegetation. 147
tion of much earth. Spirit of urine had the fame effe&s ; but fp. fal. ammon. made with lime, had not. Brown paper dipt in it, burned like a match. Thefe experi- ments mow, that it contains abforbent earth, volatile fait, the acid of nitre, and fea-falt.
HE diftilled it for five days, and nothing but phlegm, very much charged with a bi- tumen, came over. When the utmoft force of fire was applied, white clouds appeared in the receiver, which clouds condenfed into aq. reg. By two other diftillations he got fp. nitr. When oh vitr. was added to- it, there happened a violent ebullition, and aq. reg. was diftilled from it. By the affift- ance of quick-lime a fmall quantity of fp. vol. urines was got. It appears again to contain an oily fubflance, earthy matter, volatile fait in a fmall quantity, fome of the marine acid, and a great deal of fp. nltr. It is eafy to account from whence it has got the inflammable matter and vo- L 2 latile
148 The Principles of Part III.
latile fait, viz. from the putrefied vegetable and animal fubftance mixed with it. The fea-falt comes from the urine of animals poured on the matrix of nitre. But he never could extract real nitre from this nitrous earth. That cannot be done, till it has got the addition of an alkaline fait by itfelf, or contained in the afhes of vegetables. Thefe are generally added to the nitrous mafs before the water is poured on j if not, they muft be added afterwards.
THE effect: which they produce is, to join with the nitrous acid, whenever a fuf- ficient quantity of water is added for them to act: for alkaline falts attract the acid of nitre more ftrongly than the earthy bafe does, and the earth is ihaked off. Hence it happens, that in boiling, the liquor de- pofites much of this earth. There mould as much alkaline fait be added, as to fatu- tate the nitrous acid fully, and fhake off all the abforbent earth. The alkaline fait
cannot
Sect. II. Agriculture and Vegetation. 149
cannot join to the marine acid, becaufe that has already got an alkaline bafe.
IF thefe abforbent earths attract the acid of nitre from the air, in the manufacture of nitre, furely they will do the fame when laid on the earth, and be converted to the fame fait, confiding of the nitrous acid and an abforbent bafe. It is not, therefore, a real nitre, as was thought, which is the caufe of vegetation, but an imperfect ni- trous fait. This reafoning admits yet of ilronger proof, when we confider, that this very fait exifting in hard waters, has al- ready, by experiment, appeared to be a great affiftant of vegetation j and that an artificial one, of much the fame nature, compofed of lime and fpirit of nitre, when joined with a proper quantity of an oily fubftance, rendered a poor foil remarkably fertile.
IF this reafoning is juft, the effects of
different manures on the ground mould be
L 3 vifible,
150 ¥he Principles of Part III.
vifible, in proportion to their ftrength of attracting acids. This happens really fo in fact, and is a fhong confirmation of the truth of our reafoning : for afhes have the ipeedicft effects of any manure j becaufe the alkaline falts which they contain attract acids Wronger than any body. Soot and dung come next, which are volatile alka- lines, whofe attraction comes next to the firft; then the clafs of abforbent earths. The fame obfervation is made of the marls ; for, according to their rank as attracters of acids, fo they operate on ground j firft fhell, next clay, and laft of all ftone marl ; which will fometimes continue in the ground four or five years before it ihow any effects. The fame turn all thefe ma- nures keep in lofing their effects ; for the fooneft converted to fait muft be the fooneft exhaufled.
AN objection will naturally occur to every one againft this opinion, though fupported by the greateft Strength of experiment i
which
Sect. II. Agriculture and Vegetation. 1 5 1
which is, That no fuch nitrous fait is got from fertile earth. In general, thefe abfor- bent particles are in fuch fmall proportion, even in the richefl foil, and fuch a fmall degree of fermentation is carried on in it, that there are only a few of thefe particles, and thefe too on the furface, capable of being converted to this fait j and they are no fooner converted than abforbed by fome plant. Thefe confiderations {hew, that little of this nitrous fait is to be expected from any foil. That it is fometimes got, appears from this paffage of Lord Bacon, Hift. vit. et morf. Certiffimum efty quamamque terram licet puram, neque mtrofn admixtam, ita accumulatam et tetfam, ut Immunisfit a radiis folisy neque emittat aliquod vegetabile^ colligere etiam fatis copiofe nltriim.
ALMOST every perfon who has examined the contents of this foil, has denied, how- ever, the exiflence of this nitrous fait in it. Let us apply to experiment for a decilion of
this queftion.
L 4 Exf.
152 $be Principles of Part III.
Exp. 37. To put this queftion beyond all doubt, I took from a molehill fome rich foil in the month of O£tober> poured water on it, and filtered that water through brown paper. This liquor, when boiled up, was yellow, and tafted faline. The fait ap- peared plainly to be nitrous ; as brown paper, dipt in this liquor, and dried, burnt like a match. On an addition of ol. tart. p. d. the liquor turned milky, and let fall a white powder ; which mows the fait to be of the fame nature with that of hard water. At firft, I could get no fait by cryftallifation, as the liquor was very unctuous, and in fmall quantity* But on treating it in the fame manner as the manufacturers do the materials of nitre, viz, adding fome quick- lime to feparate the oil from the falts, and allowing it to (land fome days, I got from it a true faltpetrc. This experiment mows the faline part of the vegetable food to the eye.
Sed. II. Agriculture and Vegetation. 153
FROM what has been faid we may learn, Cor. i. That as hot weather hurts the formation of nitre, by exhaling it, and as the winter and fpring is the time in which it is moftly generated, all dung fhould be laid out in thofe feafons.
Cor. 2. As thefe manures become fer- tile by the action of the air, the longer they are expofed on the furface of the earth, fo much the fafter will they be converted to the nitrous fait. Farmers are now con- vinced of this from experience : but fuch bodies as contain a nutritive juice already formed, as woollen rags, hair, horn-ihav- ings, leather, faw-duft ; or thofe which already exifl in the form of a neutral fait, fuch as fea-falt, cannot be benefited by the influence of the air. Experience has like- wife confirmed this obfervation. Thefe are ftrong proofs of the juftnefs of the pre- ceding reafoning.
Cor.
The Principles of Part III,
Cor. 3. As the north wind is obferved to bring moft of the nitrous acid, it would feem to follow, that banks which have a north afpect mould receive moft of it. It is obferved, that they are, in general, richer than thofe of a fouthern afpeft. As the former have not fo much fun as the latter, they mould be lefs fruitful : but our theory of vegetation affords a fufficient reafon for this fadt.
Cor. 4. It appears, from the manufacture of nitre, that all thofe abforbent meagre earths ufed in agriculture, will be rendered more capable of anfwering their purpofe, by an addition of fome putrid fubftance, vegetable or animal, to open their texture, and make them more pervious to the in- fluence of the air. Hence the advantage of mixing animal or putrefied vegetable fubftances with chalk, marl, lime, or the
afhes of vegetables.
Cor.
Setf. II. Agriculture and Vegetation. \ 5 5
Cor. 5. As the procefs for preparing ve- getable food is the fame with that for making nitre, farmers mould imitate the manufacturers of nitre, and the nearer they approach to the methods found moil: con- venient to increafe the proflucT: of nitre, the more will they multiply the vegetable ali- ment. In France all old walls and houfes belong to the King, and are made ufe of for the extraction of faltpetre. The King of Pritjjia> by a regulation of confummate policy, has eafed his fubjedts of this bur- then, fhortened the procefs, and increafed the quantity of faltpetre. He has ordered walls of certain dimenfions to be built near every village ; they are compofed of the earth of granaries, ftables, or cellars, mixed with other fat earth. They are built to ftand fome years, till they are fuf- ficiently impregnated with faltpetre. It is obferved by Dr. Pietfch in his Penfesfur k generation de nitre, that the people employ- ed in thefe works, are yet very ignorant,
that
156 the Principles of Part III.
that they might meet with much fat earth below the furface, very fit for their pur- pofe, and that there mould always be a proportion of abforbent or calcarious earth in thefe walls. He fays, that there is al- ways leaft nitre on the fouth fide of the wall. He orders, that all vegetables mould be pulled from the walls, as they confume the nitre j that no cattle mould be allowed to come near them, as they are fond of it -, and that they mould be covered with ftraw, to hinder the rains from warning off the nitre : what ought then to hinder our farmers from making fuch walls of fat earth, dung, efpecially that of pigeons, ftraw, which will take a time before it rots, and a fmall proportion of lime, marl, or fhells ? Moft of thefe materials will be found every where. In two years they would become a very rich manure. They would operate inftantly j whereas, it takes two years before many of our manures have a fenfible effecl: on the foil. Although heavy rains warn off the nitre, yet a gentle
moifture
Se6t.II. Agriculture and Vegetation. 157
moifture of the materials is of ufe, as it is neceflary to the attraction of all falts. It has been obferved, that the fbuthern fide of thefe walls has lefs nitre. To remedy thefe defects, I would propofe, that the wall fhould be (hadowed on the fouth by a hedge, which will keep off the rays of the fun, hinder it from turning too dry, and allow the air a free paflage. The putrefac- tion, which goes on in fuch a fituation, will be of great advantage to the procefs.
PART
1 158 ]
PART IV.
SECT. I.
Of opening and pufoerifmg the foil.
IT is not only the bufinefs of the farmer to provide food for plants, but to take care that they are able to reach that food. It is of no ufe if the roots cannot pierce the ground, to get at it. Hence the ne- ceffity of opening or pulverifing the foil. Plants are fed moftly by their roots ; nor do they begin to grow, until thefe roots are fo numerous as to nourHh both themfelves and the ftem. The wider thefe roots are fpread, the more nourimment will the plant receive, the ftronger will it be, the larger will it grow, and the better will it anfwer the defign of nature.
BUT this is not the only view with which we fhould favour the growth of the
root,
Se&. I. Agriculture And Vegetation. 159
root. That part feems to be the great caufe of fecundity; for it not only nouriihes the plant, but fends up many moots and plants itfelf. A fmall piece of the root of many different plants will breed a plant. Many ftalks arife from the roots of all the different grains, long after the grain itfelf is corrupted. Hence, the more roots the more chance of plants : but the quantity of roots feems to depend, in a great meafnre, on the opennefs of the foil.
THE foil may indeed be too loofe; for it muft have a certain confiftency and cc- hefion to fupport plants. The gravelly foil is the worfe of being often ploughed. It is obferved, that a light foil, when much dunged, produces a worfe crop of peafe than when not dunged. But too great loofenefs is a rare fault, and is fooner re- medied. Too great ftiffnefs of the foil is what the farmer has moft frequently to
ftruggle with.
LET
j6o ¥ke Principles of Part IV.
LET us, then, examine the methods by which it is kept loofe. Thefe may be di- vided into natural and artificial.
S *E C T. II.
Effetfs of the atmofpbere.
THE alternate viciflitudes of the air, are the chief means that nature makes ufe of to attain this end. Heat and cold, moifture and drought, contract and dilate it by turns j and, by thefe alternate motions, (hake the particles afunder. But there are no means fo efficacious as froft and thaw. Every one muft have obferved, how loofe the foil is after a froft. Many vegetables are at this time ejected out of the earth altogether.
FROST feems to act in different ways.
ift, By changing into an elaftic ftate much
of the fixed air, which muft fhake and
open the ground, to gain, an exit. 2dly,
By
Hi. Agriculture and Vegetation* 1 6 1
By the dilatation of the water, as it freezes In the earth, the adhering particles mufl be feparated. 3dly, The particles of water (hooting out in the manner of falts, muft cut and divide the foil.
Cor. That the ground may receive, in the ftrongeft manner, the good effects of froft, it would appear reafonable, that it mould get one ploughing before the froft comes on. One furrow at this time will attenuate it more than two afterwards. Re- gard muft always be had to the climate; for where much rain falls in the winter, this practice would prove pernicious, by expofing the foil to be warned away.
SECT. III.
Change of fpecles.
THERE are fome plants defigned by the author of nature to fix the foil j there are others defigned to open it. One
M great
i6a We Principles of Part IV.
great divifion of plants is into the fibrous and carrot rooted. The fibrous-rooted di- vide directly into fmall fibres, which run in all directions, but moftly horizontally; the carrot-rooted fend one great item di- rectly down, which has lateral fibres. The former, in which clafs are reckoned all the white grains, rye-grafs, &c. confolidate the ground ; while the latter, in which clafs are reckoned the liguminous plants, carrots, turnips, clover, &c. attenuate and loofen the foil exceedingly. The clover is often ejected altogether out of the ground after a froft.
THIS effect muft depend on the nature of the roots. The fibrous roots muft bind the foil together like fo many threads, while the carrot root defcends like a wedge, and by its mere mechanical force cuts the earth; perhaps the latter may operate, likewife, by feparating more moiflure from Jt$ root to keep the earth loofe. Some plants appear to have this quality. A
fprig
Sed. III. Agriculture and Vegetation. 163
fprig of mint, which has fome roots in water, and fome in earth, will, according to 7#//'s experiment, moiften the earth from its roots. The liguminous plants, by covering the foil, keep it moift, hinder the fun to confblidate it, and deftroy the weeds which help fo much to bind it. Hence the reafon why a change of fpecies meliorates the foil fo much. When the ground is often fowed with white grain, it turns ftiff. A crop of peafe, beans, or clover, pulve-
rizes it again.
FA R M E R s have difcovered, by expe- rience, that all the fibrous-rooted plants impoverish the ground, and do not thrive when they fucceed one another ; while the carrot-rooted enrich the foil, and may fol- low one another with fuccefs. The latter, by opening the ground, make the influ- ence of the air on it reach deeper, and con- fequently help to produce more of the ve- getable food ; while the former, by conib- lidating the ground, fhut out in a great •'". M 2 mea-
1 64 The Principles of Part IV.
meafure, the influence of the air, and make the ground lefs fertile.
It is remarked, that not only a change of fpecies, but alfo a change of grain, is necef- lary : for the fame grain fown in the fame ground is obferved to degenerate. This de- pends on another caufe. It feldom happens, I believe, that the vegetable food is of a due mixture and confiftency. As foils are ge- nerally either too wet or too dry, too light or too ftiff; fo muft the vegetable food be either too thin and watry, or too thick and gluy. The vegetable muft at laft be hurt from a conftant fuccemon of one fort of food, and can only be recovered by a foil poflefTed of oppolite qualities »
SECT.
Sect. IV. Agriculture and Vegetation. 165
SECT. IV.
Of ploughing*
PLOUGHING is the artificial method of pulverizing moft known and moil practifed. It ads in two ways ; by an im- mediate mechanical divifion and trituration of the foil, and by a more frequent and extenfive expofition of it to the influence and viciffitudes of the atmofphere. I believe the latter operation is the principal one j for fo grofs an inftrument would feem very unfit to prepare the earth to enter the capillary veiTels of plants. Its effects, however, are very remarkable. They are beautifully and ftrongly illustrated by the ftory related by Pliny of Cairn Fiirius Crc- fmus. That farmer, having better crops than his neighbours, fell under the fufpi- cion of witchcraft, was accufed before the people, and faw himfelf ready to be con- demned to death. When the tribes were M 3 going
1 66 The Principles of Part IV.
going to vote, he at once produced his ruftic inftruments, of a greater fize than common, larger oxen, and heavier ploughs ; and added thefe remarkable words: Vene- faiamea,Qu£zrites>h(Zcfunt; nee pojum rcobls oftendere, aut in forum adducerey lucubra- tions meas3 vigilias^ et fudores. He was unanimoufiy abfolved.
THE good effects of ploughing depend entirely on the drinefs of the ground: for if it is wet, the ground is confolidated in- ftead of being opened 3 and remains in that ufelefs ftate till the next winter's froft loofens it again. None but dry bodies can be re- duced to a powder.
THE farmer mufl open the ground as deep as the roots of his corn penetrate, that they may find an eafy paffage : and yet he muft take care not to go below the foil in ploughing, elfe he will bury what has been benefited by the air, and expofe to the air what perhaps cannot. Hence the plough
mufl
Seft. IV. Agriculture and Vegetation. 167
muft be proportioned to the depth of good foil,
IT feems flrange, that there is not a more certain way of fixing the depth of the plough, and preferving it in that precife fituation which the foil requires, than the attention of the ploughman. That muft be often fufpended by external objects and fatigue ; and then the cattle and foil fuffer. Does not the wheel-plough remove this objection ?
THE ftiffer the foil, the oftner mould it be ploughed. Clay cannot be ploughed too often i lighter foils perhaps may. It is allowed by many farmers, that the gravelly foil may be hurt by too frequent ploughing.
As this operation depends on the prin- ciples of mechanics, and not on thofe of chymiftry, I mail leave it almoft untouched to the confideration of fome other perfon. It is a fubject worthy of attention j and al- M 4 though
1 68 Vie Principles of Part IV.
though well enough underftood, perhaps, for common practice, yet has it not been reduced to that mathematical exaclnefs which all mechanical agents are capable of. I wifh that fome practical farmer, fkilled in mechanics, would lay down the principles on which ploughs ought to be conftru&ed, and ploughing conducted. He would merit much from the community.
SECT. V.
Of compofts.
THERE is another method which art ufes to keep the foil loofe ; and that is, by the admixture of putrid and fer- menting bodies. We have feen that thefe bodies have a ftrong intefline motion before they are laid on the ground : they continue that afterwards, though in a fmaller degree. The fat foil of church-yards fwells fo much when expofed to the air, by its fermenta- tive power, that it will not go altogether
into
Sect. V. Agriculture and Vegetation. 169
into the fame hole out of which it was dug. Clay, which has fo few putrefcent particles, is the moft adhefive foil of any. We have feen already how much (hells, when they begin to putrefy, open the foil.
BUT there are other comports, though not of the putrefiable fort, which have this attenuating power in a flrong degree. In this clafs are all the marls, but efpecially the fofteft, fuch as the clay marl. We have found how readily they lofe all ad- hefion in water, and fall down into a powder. The fame power they commu- nicate to other earth, even to the moft ad- hefive. The following experiment is a proof of this.
Exp. 38. Take equal parts of marl and clay, mix them well together, and dry them -, when this compounded fubftance is put into water, it falls by degrees to the bottom of the glafs in the fhape of a powder, while a ball of pure clay remains
quite
1 jo The Principles of Part IV.
quite undiflblved in water. This ihovvs the ftrong attenuating power which marl has, and which no other body can come up to. It is obferved, that all clay grounds, after they are marled, dry fourteen days fooner than what they did before. This is owing to the foil being more loofe, by which means the water pervades it more eafily.
I KNOW that this opinion contradicts the common "one, that marl is not fit for clay grounds. From whence the latter has taken its rife, I know not, if it is not that bodies of fuch a limilar appearance cannot be allowed to benefit one another. But the experience of many counties where marl is ufed, and where the foil is generally a deep clay, contradicts this vulgar opinion. The following experiment puts it beyond all doubt.
Exp. 39. 1 filled a pot with clay of the fame kind I had ufed in the former experi- ments,
Sedt.V. Agriculture and Vegetation. 171
ments, which had been expofed to the air for four months, and feemed to have no mixture of any other earth with it, as it made good brick, with the addition of fand; and had been taken up feven or eight feet below the furface. This pot I mall call N° i. Pot N° 2. was filled with equal parts of clay and marl j N° 3. with equal parts of clay and foured lime 5 N° 4. with equal parts of clay and fea-fand well warned j N° 5. with equal parts of clay and dung. Thefe different compofitions were turned daily. On the 2 6th of April fix grains of barley were fown in each.
May 14. N° 2. had two plants, above ground ; N° 3 . had four.
May 17. N° 2. had fix ; N° 3. had feven, two of which were from one grain 3 N° 4. and 5. had one each.
May 21. N° i. had five, of which two were an inch and a half high -, N° 2. had
fix
j 72 *rbe Principles .of Part IV.
fix two inches high ; N° 3. were about the fame height 3 N° 4. had two, one of which was one inch high j N° 5. had three, each two inches high.
June 4. N° 2. talleft and greeneft ; N° 3. very near it; N° i. and 5. of an equal height, but the latter of a very light colour , N° 4.worftofall.
Aug. 20. N° i. about nine inches tall, and much withered. The roots feem not to have pierced the clay, but to have funk along the cracks. N° 2. has nine ears, and thofe of a very deep green colour. N° 3. has eight, but not of fo deep a green. N° 4. has five, and thofe much fmaller. N° 5. has nine, almoft as good as N° 2. I had no opportunity of feeing them after- wards,
Cor. i . By this experiment it appears, of what great advantage it is to manure clay $ for, of itfelf, pure clay is not capable of
pro-
Sect. V. Agriculture and Vegetation. 173
producing good plants, becaufe their roots are not able to penetrate it.
Cor. 2. Sand appears, in oppofition to the common opinion, to be the worft manure of thofe ufed. It cannot indeed feparate the minute particles of the clay, which is the only ufeful feparation for the growth of vegetables. A little fand rather feems to increafe the union of the particles of clay, as appears from the manufacture of brick.
Cor. 3 . Lime feems to be a good manure for clay. What I ufed had been foured for fome time. The effect which the air has on it, in changing it from quick-lime to effete lime, muft open the ground con- fiderably.
Cor. 4. Dung and marl appear to be the beft manures for clay. The former has a flrong fermentation ; the latter lofes all co- hefipn when water is added.
SECT.
174 ¥ke Principles of Part IV.
SECT. VI.
Of vegetation.
IT is worth our pains to take a fhort view of what muft happen to the vege- table food in the vefiels of plants. To enter into a difcuffion of the anatomy of plants, would be foreign to the fubject. I mall take that as demonftrated by botanifts.
THE nitrous fait being formed on the furface of the foil, will be warned down by the dews and rains. It will difTolve what oils it meets with in its way, and conftitute with them a faponaceous juice, containing, befides the former principles, fixed air and fixed fire. This juice will be retained in the foil ; becaufe I mowed by experiment, that fertile foil a&ed like a fpunge with refpect to water. This na- tural defcent from gravity, and the natural afcent from the heat of the earth and in- fluence
Sect. VI. Agriculture and Vegetation. 175
fluence of the fun, muft keep the nutri- tious juice in a continual motion ; fo that it muft be continually applied to the roots of plants deftined for the admiffion of nou* rifhment.
THE firft queflion which can raife any doubt here is, In what manner do the juices arife to the tops of plants and trees ? Mal- pighius thinks, this is owing, in a great meafure, to the air-bladders which he difco- vered in the fkucture of plants, and which he thought behoved to dilate and contract, according to the different changes of heat and cold which happen in our atmofphere. To me it does not appear, that the dilatation of fuch vefTels would force it more upwards than downwards. I mould rather imagine, that fuch a dilatation would ftop the motion altogether.
THE .caufe commonly afcribed, viz. the action of capillary veflels, appears to me fufficient for that end. Hales has demon-
ftrated
1 76 The Principles of Part IV*
ftrated the fact to the eye, by feveral experi- ments, in which a part of a branch, being cut at both ends, and having its under part immerfed in water, a moifture was imme- diately perceived in its upper part. This effect of capillary tubes muft arife from the attraction betwixt the fubflance of which they are compofed and water.
THE attraction betwixt wood and water appears to be very ftrong, by an experi- ment related by Dr. Taylor, In the Philofo- phical Tranfatfions, N° 368. He hung at a pair of fcales a piece of fir board, foak- ed it in water, weighed it, and then im- merfed it again in water. To raife this piece of wood, which had a furface of an inch fquare in contact with the water, fifty grains over and above its former weight were required. The additional weight in the different trials, he fays, was always proportional to the furface. The diftance of the under furface of the board from the furface of the ilagnating water,
at
Sect. VI. Agriculture and Vegetation. 177
at the time of reparation, meafured up- wards of -r.ro of an inch. This additional
\
weight is the real meafure of the attraction betwixt that furface of wood and water in, contact.
THERE is another force that muft con- tribute to raife the fap, viz. the natural at- traction betwixt the conftituent parts of thq fluid. This muft certainly be the cafe, when the fap moves quickly, as in the vine in the bleeding feaibn. Both thefe caufes acting, and the evaporation going on con- tinually from the fuperior parts of the vef- fels, the fap rifes from the roots of the plants to the extremity of their branches.
t
BUT nature does not intend that this (hall be done too quickly. There are many fpiral veffels, and many cells into which the fap is depofited, and by which it muft be retarded. In thefe the fap will be much altered in its nature, by the mo- tion of the plants, by the continual mo- N tions
178 eHe Principles of Part IV;
tions of the air-veflels, and perhaps by the particles of light taken in at the leaves. The juices are rendered richer by the expul- fion of the watery particles. The remaining ones are partly applied to the extremities of the veflels, which run in all directions, ho- rizontally as well as perpendicularly, and make the plant increafe in breadth and length j and partly go to the formation of leaves, flowers, fruit, &c.
IT is eafily conceived how plants, by the different combinations of the five principles of which their food is compofed, and the combination of thefe in different de- grees, mud differ very much in their juices and products. If their groffer particles are to be feparated for any ufe, the fub- tiler are all carried off by lateral veflels, until none are left but what are wanted ; if the fubtiler particles are to be ufed, they are to be feparated by fmall veflels fitted to receive them, implanted in the larger, or in the cells where the juices are depo-
pofited
Sed. VI. Agriculture and Vegetation. 179
iited. In this way particles of any fize may be lodged in any part of the plant. Hence all that variety in the falts, oils, cmd figures of plants. Hence all that va- riety of fmells, taftes, virtues, and other qualities.
How ftrong the power inherent in the veffels of plants to change and alter thofe fubflances which are taken in> appears from an experiment of Homberg. He filled two pots of earth mixed with fome falt- petre. Into one he put creffes, which is an alkalefcent plant, and affords a volatile alkaline fait, but no acid ; into the other fennel, which is an acefcent plant, and affords an acid on diftillation, and no al- kaline volatile fait. He filled two other pots with earth, which had all its falts warned out, if there were any in it. Into one he planted fennel, and into the other creffes, as in the former. The two plants in the nitred pots grew much better, and weighed much more than in the pots with- N 2 out
i So 'The Principles of Part IY»
out nitre. The creffes in the nitred pot, when diftilled, gave no acid felt, though fed on a fait which contained an acid. The fennel fed in the wa/hed earth gave an acid,, though there was none in the earth. This experiment mows, that the veffels of plants have a power of changing the falts taken in from the earth, into their own particular natural one, probably by combining them with different proportions of water, oil, earth, air, and the particles of light which iflue from the fun,
BUT how fhall we account for die diffe- rent external forms of plants ? Shall we fly to the immediate hand of the Supreme Being ? or, as this ought to be the laft ftep in philofophy, can we find no chymical agents capable of this effect ? From many experiments, which mow the natural inhe- rent power in falts, efpecially the nitrous kind, to run into vegetations, as they are called, and to take the figure of plants, with branches, leaves, nay even an appearance
of
Sect. VT. Agriculture and Vegetation.
of fruit, owing to the ftrong attachment fubfifting between them and water, I have often been led to think, that the vegetative power of plants, nay their particular forms of vegetation, were owing to that vegetative power inherent in their falts. In effect, we fee that vegetative power ftrongeft when moft fait enters their veffels ; that is to fay, in the fpring.
THUS I have endeavoured to account for the effects of manures on the different foils, and for the rife and changes of the vege- table food in the veflels of plants, from thofe remarkable attractions and affinities which the Author of all has endued the fmaller particles of matter with, Thefe are not, as is commonly imagined, mere paffive bodies; but active, vigorous, and capable of producing thole changes by which nature is fupported. I have de- monftrated thefe affinities by experiment j I have afTumed no other principles ; I have built my whole plan on thefe; I hope, N 3 there-
1 82 "The Principles of Part IV.
therefore, that its fimplicity will be a ftrong proof of its truth.
BUT whence thefe elective attractions which move the whole ? Whence acquires matter the power of acting without itfelf? for that muft be the cafe, unlefs we fup- pofe an endlefs chain of material agents. Whence but from an immaterial being, who, by his order, firfl fixed thefe proper- ties to matter, and, by his immediate will, conftantly fupports them in the fame tenor ? Jt is on particles too minute for human eyes, that the omnipotent hand chufes to exert itfelf, and on their powers to erect this beauteous fyflem. Hence the origin of all motion, adhefipn, increaTe, and or- ganifed matter,
BUT as all individual forms were defign^ ed to be. of finite duration, he eftablim- ed other particles with repulfive powers, and mixed the feeds of dnTolution with the firft rudiments of organical life.
Sect. VI. Agriculture and Vegetation. 1 83
the veflels are pervious, and the motion of the fluids fubfifts, the attractive overba- lance the repulfive powers, and the vege- table or animal life continues. But when that motion ceafes, and other circumftances concur, the repulfive become too ftrong for the attractive powers, duTolve the compo- fjtion, and reduce the body to thole par- ticles of which it was at firfl made up. This is the great circle that Omniicience has marked out, and Omnipotence circum- fcribes itfelf to, for the greateft good of the whole.
N 4 PART
1 84 tte Principles of PartV,
PART V. SECT. I.
Of weeds*
THE laft article which we propofed to confider was, what impediments there were to vegetation, and the methods of removing them. Thefe impe- diments are fuch as either belong to the foil or to the plants. We mall treat of them according to this divifion.
AMONGST the impediments of the foil, J clafs all fuch vegetables, as, being of no ufe to the farmer, are called weeds, or /«- utiles herbce. Thefe become hurtful to the growth of more valuable plants, by con- fuming part of the nourishment. I here clafs alfo thofe roots called wreck in this country, which run through the ground often in fuch plenty, that they bind the
foil,
£ec~h I. ' Agriculture and Vegetation. 185
foil, hinder the roots of the corn to fpread, and draw up a great deal of nourishment. Thefe are generally the roots of the quick grafs. The reft harrow has a large root, which goes very deep.
THESE weeds, and the roots belonging to them, are deftroyed, I. By fummer fal- lowing. They are torn up by the plough when they begin to fhoot, their roots are expofed to the fun, they fopn wither, and are killed ; or elfe they are juried below the furface.
2. A METHOD much analogous to the former, is trenching eighteen inches deep. This buries the plants fo deep that they die ; but this can only be put in practice where the foil is good to that depth.
3. ANOTHER method of killing ufelefs plants is, to hoe them when young. That effectually roots them out.
4. No
1 86 the Principles of Part V.
4, No plants can grow without a fuffi- cient quantity of frefh air, which is as ne- ceflary to the vegetable life as to the animal. Whatever plants cover the ground clofely, deftroy all thofe which grow below. Hence a good crop of peafe kills all weeds by overshadowing them ; in fo much that the farmer aflures himfelf of a good crop of wheat if the peafe are good. If they are not, a greater quantity of weeds comes up than ufual; and he never can expedl any of the three following crops to be good, wnlefs he gives the ground a fallowing.
. IT is in this way, likewife, that fog is deftroyed. The inclpfure is fhut up from the middle of May to the beginning of De~ cember, and then fed from that time to April, After that it is faved for a crop of hay. The fog being fo long covered by two fucceeding crops of grafs, is cut off from the benefit of the air, and fo di-es.,
5. THERE
Sett. II. Agriculture and Vegetation. \ 87
5. THERE is yet another way of deftroy- ing thefe weeds ; and that is, by marl. I have feen broom effectually killed by marl. I have feen a crop of wheat growing on a field which was partly marled and partly not. That part of the field on which marl had been laid, was free from all weeds, while the other unmarled part was full of them. The fame wheat was fowed over the whole field. I can account for this effeft of marl in no other way than this, that the grain is brought up fo fpeedily as to be able to choke and deftroy thefe weeds.
SECT. II.
Of a ivef foil.
THERE is not a greater enemy to ve- getation than the too great moifture of the foil. It is always owing either to a ftratum of rock, or of clay, generally the latter, below the furface, which not allowing the rains to pafs through, they
can
Principles of Part V.
can get off in no other way than by evapora- tion; a very flow method, when compared to filtration. Farmers exprefs the effects of water by faying, that it fours the ground. It is not meant by this, that the ground becomes really acid, but only that it is changed in its nature, and rendered unfit for vegetation. The natural product of this foil are, rufhes and four grafs; which lafl appears in the furrows, but feldom in the crown of the ridge; is dry and taftelefs like a chip of wood ; and feels rough, when ftroked back- wards. The natural effect of ftagnating water I take to be, its putting an entire flop to the admiffion, and confequently to the influence of the air.
THIS excefs of moifture is carried of? by a proper difpofition of the furrows, accord- ing to the natural defcent of the ground, by which the water will have an eafy paf- fage to get away. It is likewife material that the furrows mould be ftraight : for the flraighter the furrow, the morter time will
the
Sed. III. Agriculture and Vegetation. 189
the water remain in the. ground. It would appear likewife* that the narrower the ridges were made, provided they were above the ftagnating water, the fooner would the water fall through them, to get at the furrow. The furrow mould be made with a double mouldebread plough, that both its fides may flope. Marling the ground, as I faid before, makes it drier, by opening and loofening the foil. A field manured in this way, will be fit fourteen days fooner in the Ipring for ploughing. If thefe me- thods do not fuceeed, on account of water arifing from fprings, open or hollow drains muft be made at different diftances. Open drains feems beft, if the fprings be not toq many,
SECT. III.
Of rains.
GREAT rains are considerable impe- diments to the proper concodlion of the juices in the veffels of plants, and alter
very
190 The Principles of Part V*
very much the nature of thefe juices. Says a French author: Rn /' armee 1705, // tie plu prefque pas en Juin et en Jiiillet, et ks bleds etoient excellent. Mais en 1707, quoi* quil y ait eu de chaleurs extraordinaires, i I plu ft abondamment pendent les deux mots, que le bles riont rien valu, et ces font pref- tout cchaujfcs.
I? is obferved, that all plants grow very faft after rains j not only the tefreftrial, but the aquatic. The latter can never be fup- pofed to want water ; fo that this effect muft proceed from fome other caufe, than the increale of nourimment by the roots. The fame effect is obferved to happen, when the fky, from being clear, grows cloudy and ftormy. Perhaps their too great perfpiration may be flopped: perhaps the moifture is fucked up by the pores of the leaves and wood : perhaps, as their nou- rimment depends on the circulation of their juices, and that circulation on the contrac- tion of the trachea or air-veffels, according
to
Sect. IV. Agriculture and Vegetation. 191
to MalpigbiuS, the fudden contraction fills the fmalleft and remoteft veffels with nou- rifliing juices ; and does it with Ibme force, which may lengthen the vefTels. As the veflels are more full of water, and the per- fpiration lefs than ordinary, it is no wonder that the juices are not well concocted, and the grain bad.
SECT. IV.
Of faulty feed.
HAVING confidered the impediments to vegetation which arife from the ground, let us next take a fhort view of thofe which arife from the feed. To pro- duce ftrong plants, we muft chufe ftrong feed, Grain which has been ftarved in meagre grounds cannot thrive.
OLD grain will not grow; and there- fore, farmers always chufe the laft year's .corn. It is thought that grain will not
grow
*rke Principles, of Part V.
grow when it paffcs the age of five years : but the time cannot be precifely fixed, for that muft depend on the drinefs and oili- nefs of the feeds. All the oily feeds keep long, fome of which will lie in the earth for fifteen or twenty years. Two months after the great fire in London there ap- peared a great crop of a Ipecies of eryfi- mum> where there had been houfes for a thoufand years. Mr. Reaumur fbwed fome of the grain which had been preferved in the citadel of Metz for one hundred and thirty years; and which made very good bread. In three weeks fome of the grains were fwelled, and fome not. In fix weeks no grains were to be found.
THE caufe of ilerility in old grains feems to confift in the vefiels lofing that fupple- nefs which is neceffary for their extenfion, and filling with water; and in the con- tained liquor lofing that gluinefs which is neceflary for nutrition. This appears from the brittlenefs of the grain, which becomes
fo
Sect* V. Agriculture and Vegetation. 193
fo by the evaporation bf the mucilaginous parts.
SECT. V.
Difeafes of plant s>
ALL organized bodies, confining of containing veffels, and contained fluids in motion, are fubjecl: to have thofe fluids altered, and that motion vitiated. Hence the difeafes of plants. Bourne- fort has, therefore, judicioufly clafled thefe difeafes into thofe which arife, i. from too great an abundance of juice; 2. from too little j 3. from its bad qualities ; 4. from its unequal distribution ; 5. from external accidents*
Too great abundance of juices muft caufe ftagnations, corruptions, too great a quantity of water-moots, varices, cariofities, &c. It feems to be in this way that too much rain operates. The fmut, which is a corruption of the grain, ought to be clafTed O here i
194 *The Principles of Part V.
here; becaufe it happens moft to weak grain, and in rainy feafons. It may, like- wife, be communicated by infection, if I may fo fpeak ; and the fmut, like other con- tagious difeafes, may be transmitted from the infected to the healthful grain. The ex- periment, I was informed, has been tried. Some fmutty grain was fown along with very good feed j and the produce appeared very fmutty. Nor ought it to furprize us, that this mould happen to the juices of plants, when we find, by daily experience, that the juices of animals aflume the nature of the contagious ferment communicated to them. This difeafe is prevented, in a great meafure, by fteeping the grain in a pickle of fea-falt. This operates in two ways. It firengthens the feed, and fits it for expelling the fuperabundant watry juices -, and, by its great weight, fufpends all the faulty grain ; fo that none but the heavieft and ftrongeft fall to the bottom, and are made ufe of.:
DUNG
Se£t. V. Agriculture and Vegetation. 195
DUNG feems to prevent other difeafes arifing from too great a quantity of moif- ture. An experiment, performed by a gentle- man of my acquaintance, will fhow this effecl: of dung in a flrong light. He fal- lowed two acres of poor ground, which had never got any manure, with a defign to fow wheat on it j but altering his fcheme after- wards, he laid feme dung on a fmall part of it, and fowed the whole, after it had got five furrows, with barley. A great quantity of rain fell. The barley, on that part which was dunged, was very good j but what was on the reft of the field turned yellow after the rains, and when ripe, was not worth the expence of reaping. This experiment {hows, that the moifture and poverty of the foil was the caufe, and that the dung was the cure of this difeafe.
PLANTS and trees certainly decay for
want of proper nourishment. This is the
caufe why the leaves fall ofT at the approach
of winter. It appears plainly from the fol-
O 2 lowing
1 g6 The Principles of Part V.
lowing experiment. Ingraft an almond tree on the black damafk plumb : for the firft year the almond tree thrives very well ; but after that they both decay (lowly and die. The reafon is, becaufe the former vegetates much fooner than the latter ; and, therefore, requires nourishing juice when the former has it not. While young, it is eafily fupplied ; but when it grows larger, it exhaufts the plumb, and is ftarved itfelf. If the plumb is ingrafted on the al- mond, the juice rifes in the latter, when the former is not fitted to receive it, and it dies of repletion.
DU HA MEL, in Mem. acad. des fciences for the year 1728, mentions a difeafe, called le morf, which attacks the faffron in the fpring ; and is owing to a plant of the fpecies of trefoils, that has no ftem, fixing fome violet-coloured threads, which are its roots, to the roots of the faf- fron, and fucking out its juice. This difeafe is prevented by digging a trench, which
faves
Se6t. V. Agriculture and Vegetation. 1 97
laves all the unaffected. All difeafes from defeat of nourishment, are cured by the ap- plication of manures.
THE juices may be, likewife, faulty from their bad quality. When the turpentine juices of the pine and fir turn too thick, the tree is fuffocated. Sugar canes, it is faid, do not thrive fo well in rich new foil, be- caufe it affords too oily a juice, which is not fo good for fugar : if they are cut when fix months old, the leaves burnt, and the ames laid round them, they afford better fugar. The alkaline fait, from the ames of the leaves, attenuates the oils, and makes a better faccharine juice. Plants or feeds tranfported from warmer countries to cold, decay gra- dually, becaufe the juices are not fufficiently attenuated for want of heat.
THE unequal diftribution of the juices fcems to be another caufe of vegetable dif- eafes. In corn, the juice fometimes runs too much to the leaves ; cutting or eating O 3 the
i 98 The Principles of Part V.
the corn is a remedy for this, as it fends the juice to the ftalk.
EXTERNAL accidents, fuch as froft, hail, flies and their eggs, vermin, Gfc. give rife to many difeafes. There is a fmall white hard worm very common in new ground, which deftroys plants by eating their roots. Thefe worms are killed by quick-lime or Jime-water.
THE mildew is to be ranked here, as it feems to be owing to a gluy faccharine matter falling with a fummer fhower, and blocking up the perfpiration of the plant. This matter may be felt and tafted on the furface of the leaves. That it operates in this way, appears from the following fact. There is in the Brian^on, a fpecies of nut- tree, which has all its leaves covered with a faccharine fubflance, arifing from the per- fpiration of the juices of the plant. If it is in very great quantity, the trees often die,
AMONGST
Se&.V, Agriculture and Vegetation. 199
AMONGST the clafs of external accidents we may place the ef&dts which arife from the contiguity of certain plants. There are fome plants which do not thrive in the neighbourhood of others. This is obferved of the cabbage and cyclamens, of hemlock and rue, of reeds and fern. We have many examples of fuch like antipathies amongft animals. Thefe effects feem to be produced by the effluvia which are emitted by all organised bodies.
IT is furpriling that the prefent fubjed:, fo highly neceflary to the proper culture of plants, mould have been almoft entirely neglected ; fo that an inquirer finds too few fads and obfervations to be able to lay down any regular fyftem. Befides, the difeafes of vegetables feem to require more amftance, and therefore demand more at- tention, than thofe of animals ; if we regard the cure alone, and fet afide the higher rank in the fcale of creation, and confequently O 4 the
2oo *The Principles of Part V.
the higher value of the latter. Animals have a fentient power within, which, irri- tated by the caufe of a difeafe, quickens the motions of the heart and arteries, and con- tinues thefe mechanical agents till the mor-* bific particles are expelled, or the animal fyftem overpowered by them. But there is no fuch power inherent in vegetables. Unlefs a remedy is applied from without, they muft continue to labour under the difeafe. Whoever removes the difeafe of an animal, does it by directing thefe natural and mechanical motions aright, and in the way that the motive power feems to point out. But whoever removes a vegetable difeafe, muft look on the work as entirely his own, as he has got no affiftance from $he vegetable itfelf.
E c T;
5ect. VI. Agriculture and Vegetation, io t
SECT. VI.
Plan for the further improvement cf agri- culture.
THUS I have endeavoured to fhow, that agriculture is not fo uncertain and un- fcientifical an art as is commonly thought; but is reducible, like other arts, to fixed unalterable principles. I have already look- ed back, and confidered the impediments which have lain in the way of its progrels to fome degree of perfection. I mall now look forward to fee how thefe may be beft remedied, and in what manner we can aflift it in its progrefs.
AGRICULTURE does not take its rife originally from reafon, but from fact and experience, It is a branch of natural phi- lofophy, and can only be improved from the knowledge of facts, as they happen in nature. It is by attending to thefe facts that the other branches of natural philo-
fophy
Principles of Part V;
fophy have been fo much advanced during thefe two laft ages. Medicine has attained its prefent perfection only from the hiftory of difeafes and cafes delivered down. Chy- miftry is now reduced to a regular fyftem, by the means of experiments made either by chance or defign. But where are the experiments in agriculture to anfwer this purpofe ? When I look round for fuch, I can find few or none *. There, then, lies the impediment in the way of agriculture. Books in that art we are not deficient in; but the book which we want is a book of experiments.
AND, indeed, as things ft and at prefent, it muft always be fo. Mankind are my in attempting any thing, or at leaft render-
* Since thefe papers were wrote, I have read three volumes of experiments publifhed by Du Hamel^ on Tw/Ps fyftem of agriculture. They are diftinct, exact, conclufive, fo far as they have gone, and ftand a model for experiments in agriculture. What a fhame for Great-Britain^ where agriculture is fo much cultivated, and where that fyftem took its rife, to leave its exact value to be determined by foreigners !
ing
Sett. VI. Agriculture and Vegetation.
ing it public, unlefs they can make it com- plete, or erecl: fbme plaufible iyftem. This they may do in all other arts, but they cannot in agriculture. The time fo feldom comes about, and the progrefs of the ex- periment is fo flow, that one perfon can make but very few during his life. A number of experiments are to be found, not in the pofTeffion of one, but in the hands of many. The fault, then, lies not in the deficiency of fads j for chance and deiign muft have been able to furnifh many ; but of a certain, proper, and eafy channel, through which they might be conveyed to the world, without wounding
the natural vanity of mankind.
«
HITHERTO thefe fadts and experiments have been confined to converfation alone, and have died along with thofe who made them. I would propoie a fimple remedy for this. Let a committee of the Edin~ burgh fociety, not exceeding five perfons, be named for the branch of agriculture
alone,
204 The Principles of Part V.
alone, whole duty mall be, to receive fingle and detached experiments, put them in a proper drefs, if they ftand in need of it, and publifh them to the world at ftated times, like a public paper. This manner of appearing feems well calculated to raife a fpirit of experimental farming over the country.
THE narrator, on his part, fhould deli- ver the experiment in the plaineft and moft diftinft manner, and feparate the facts from his reafonings. Peripicuity and exa&nefs are the chief beauties in experi- mental writing. The plain fad mould be firfl told, with all its concomitant circum- ftances ; fuch as, the fituation of the ground, nature of the foil, previous cul- ture of it, quality of the feed, country where the experiment is made, ftate of the air, at fowing and after, with regard to heat and cold, drought and rain, wind, &c. The reafoning on the experiment fhould then follow, and fhould be fuch as
arifes
Seft. VI. Agriculture and Vegetation. 205
arifes naturally from the experiment. Al- though it is not necefTary to mention any name to the public, yet the experiment, when delivered, mould be fubfcribed by the perfon who made it, to avoid all im- pofition.
IN order to increafe the fpirit of experi- ment-making over the country, I would propofe, that this committee mould have it in their power, to grant one or more honorary or lucrative premiums, to thole who mall have delivered the moft inge- nious and ufeful experiments in agricul- ture. It is in this way, I think, that the premiums defigned for agriculture mould be eftablimed. They ought to be, not on fiich fubjects as the farmer is naturally led by his own gain to purfue ; for fuch he will generally follow, to the utmofl of Ms knowledge and abilities j but on fuch as are not fo nearly connected with gain, and make him go out of the common road. .This confinement may, however, be too
great
206 The Principles of Part V.
great at the firft fetting out 5 and it may be more advifable, to admit all experi- ments for fome time, till the fpirit be once raifed.
.
THE happy confequences of this fcheme are very evident. Farmers will begin to fee the only method of cultivating this art with fuccefs ; they will attend to minute circumftances to which they never did be- fore j they will be fond to communicate the iffue of their experiments to the public, when they can do it in that eafy and con- cealed way $ they will have a dictionary of facts to confult opon occafion ; and will be able to draw advantage from both the
0
good and bad fuccefs of others.
•
IN time this plan may afford fund fuffi- cient for fome future compreheniive genius, who, laying the different, and often feenf* ingly oppofite experiments together, and confidering all their concomitant circum- ftances, may be able to reduce the practice
to
Seft. VI. Agriculture and Vegetation. 207
to fixed and permanent rules. This good fortune feldom happens to the firft experi- menters in any art ; for they fee things in too narrow a view, and often with too prepofTefTed a mind. It is referved for that unbiaffed and found judgment, which can take from every opinion whatever truth it contains j and, from the whole united together, raife one regular, beneficial, and lafting fyflem.
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