682 



FARMERS' REGISTER 



[No. 11 



countries where marl was not to be founJ, cal- 

 cined limestone would be naturally employed as a 

 substitute. 



The elder writers on affriculturc had no correct 

 notions of the nature of lime, limestone, and marl, 

 or of their etlects ; and this was the necessary 

 consequence of the impcrlt^ciion of the chemistry 

 of the age. Calcareous matter was considered by 

 the alchemists as a peculiar earth, which, in the 

 fire became combined with inflammable acid ; and 

 Evelyn and Han lib, and, still later, Lisle, in their 

 works on husbandry, have characterized it merely 

 as a hot manure, of use in cold lands. It is to 

 Dr. Black, of Edirdiurgh, (hat our first distinct ru- 

 diments of knovvledfie on the subject are owing 

 About the year 1755, this celebrated professor 

 proved, by the most decisive experiments, that 

 limestone and all its modifications, marbles, chalks, 

 and marls, consist principally of a peculiar earth 

 united to an ai-rial acid : lliai the acid is given out 

 in burninix, occasioninu ;i loss of more than 40 per 

 cent., and that the lime in co[isc(;uence becomes 

 caustic. 



These important facts immediately applied, with 

 equal certainity, to the explanation of the uses of 

 lime, both as a cement and as a manure. Asa 

 cement, lime, applied in ils caustic slate, acquires 

 its hardness and durability, by absorbing the aerial 

 (or, as it has been since called, carbonic) acid, 

 which always exists in small quantities in the at- 

 mosphere ; it becomes, as it were, again limestone. 



Chalks, calcareous marls, or powdered lime- 

 stones, act merely by forming an useful earthy 

 ingredient of the soil, and their efficacy is propor- 

 tioned to the deficiency of calcareous matter, 

 which, in larger or smaller quantities, seems to be 

 an essential ingredient of all fertile soils ; neces- 

 sary, perhaps, to their proper texture, and as an 

 ingredient in the organs of plants. 



Burnt lime, in its first effect, acts as a decom- 

 posing agent upon animal or vegetable matter, 

 and seems to bring it into a stale in which it be- 

 comes more rapidly a vegetable nourishment ; 

 gradually, however, the lime is neutralized by 

 carbonic acid, and converted into a substance ana- 

 logous to chalk ; but in this case it more perfectly 

 mixes with the other ingredients of the soil, is 

 more generally diffused and finely divided; and it 

 is probably more useful to land than any calca- 

 reous subsiance in its natural state. 



The most considerable fact made known, with 

 regard to limestone, wilhin the last lew years, is 

 owing to Mr. Tennant. It had been long known, 

 that a particular species of limestone, found in dif- 

 ferent parts of tlie north of England, when applied 

 in its burnt and slacked state to land in considera- 

 ble quantities, occasioned sterility, or considerably 

 injured the crops lor many years. Mr. Tennant in 

 1800, by a chemical examination of this species 

 of limestone, ascertained that it differed from com- 

 mon limestones by containing magnesianearth; and 

 by several experiments he proved, that this earth 

 was prejudicial to vegetation, when applied in 

 large (luantities in its caustic state. Under com- 

 mon circumstances, the lime from the magnesian 

 limestone is, however, used in moderate quantities 

 upon fertile soils in Leicestershire, Derbyshire, and 

 Yorkshire, with good effect; and if may be applied 

 in greater quantities fo soils containing very large 

 proportions of vegetable matter. Magnesia, when 

 combined vvitli carbonic acid ifas seems not lo be 



prejudicial to vegetation, and in soils rich in ma- 

 nure it is speedily supplied with this principle from 

 the decomposition of the manure. 



After the nature and operation of manures have 

 been discussed, the next, and the last subject fi)r 

 our consideration, will be some of the operations 

 of husbandry capable of elucidation by chemical 

 principles. 



The chemical theory of fi^llowinii is very simple. 

 Fallowing affords a source of riches to the soil, 

 in consequence of the absorption of oxygen anc^ 

 the aqueous principles of the atmosphere, and sa 

 tends to produce an accumulation of decomposing 

 matter, which, in the common course of crops, 

 would be employed as it is formed. Yet in highly 

 cultivated soils, under a regular succession ofcrops, 

 properly manured, this practice can rarely be 

 advantageous : and the cases in which it is really 

 beneficial are for the destruction of weeds, and for 

 cleansing foul soils. 



The chemical theory of paring and burning, I- 

 shall discuss fully in iliis part of the course. 



It is obvious, that in all cases it must destroy a 

 certain quantity of vegetable matter, and must be 

 principally useful in cases in which tliere is an ex- 

 cess of (his matter in soils. Burning, likewise, 

 renders clays less coherent, and in this way great- 

 ly improves their texture, and causes (hem lo be 

 less permeable (o water. 



The instances in which it mn*t be obviously 

 prejudicial are those of sandy, dry siliceous soils, 

 containing little animal or vegetable matter. 

 Here it can only be destructive, for it decomposes 

 that on which (he soil depends for its productive- 

 ness. 



The advantages of irrigation, though so lately 

 a subject of much attention, were well known to 

 the ancients; and more than two centuries ago 

 the practice was recommended to the farmers of 

 our country by Lord Bacon: "meadow-watering," 

 according to the statements of this illustrious per- 

 sonage, (given in his Natural History, in the arti- 

 cle Vegetation,) "acts not only by supplying use- 

 ful moisture to the grass; but likewise the water 

 carries nourishment dissolved in it, and defijuds 

 the roots from (he effects of cold." 



No general principles can be laid down respect- 

 ing the comparative merit of the different systems 

 of cultivation and the various systems ofcrops 

 adopted in difl'erent districts, unless the chemical 

 nature of the soil, and the physical circumstances 

 to which it is exposed, are iully known. Stiff ci>- 

 hereni soils are those most benefited by minute- 

 division and aeration, and in the drill system of 

 husbandry these effects are produced to the great- 

 est extent; but still the labor and expense con- 

 nected with ils application in certain districts may 

 not be compensated lor by the advantages pro- 

 duced, and there are some stiff soils which must 

 be left in clods when sown with wheat. Moist 

 climates are best fitted for raising the artificial 

 grasses, oats, and broad-leaved crops; stiff alu- 

 minous soils, in general, are most adapted (or- 

 wheat crops, and calcareous soils produce excel- 

 lent sain-lbin and clover. 



Nothing is more wanting in agriculture than ex- 

 periments in which all the circumstances are mi- 

 nutely and scientifically detailed. This art will 

 advance with rapidity in proportion as it becomes 

 exact ill its methods. As in physical researches, 

 all the causes should be considered; a diliierence 



