SOIL. 



tnoillurt, after being heated to 88°, was expofed in a tem- 

 perature of 55° ; in iefs than a quarter of an hour it wai 

 found to have gained the temperature of the room. In all 

 thele trials the foils were put upon fmall trays made of 

 tin-plate two inches 'quare and half an inch in depth, the 

 temperature being afcertained by a thermometer of a very 

 delicate kind. 



It is upon the whole fuppofed, that nothing can be more 

 evident, than that the genial heat of the foil, particularly in 

 the fpring feafon, mufl be of the greatelt and moil ma- 

 terial ufe and importance to the raifmg plants as crops. And 

 that when the leaves are fully and completely developed 

 or fpread out, the ground or land is confiderably (haded ; 

 and any injurious influence or confequence, which in the 

 fummer feafon might have been apprehended from too great 

 a heat, wholly prevented : fo that the temperature of the 

 furface, when bare and expofed to the efiefts of the fim, 

 affords at lead, it is fuppofed, one indication of the ftate of 

 its fertility ; and that the thermometer may therefore be, it is 

 believed, fometimes an ufeful inftrument to the purchafer as 

 well as improver of lands. 



The moilture prefent in foils has likewife an effeft and 

 influence on their temperatures ; and the particular manner 

 or method in which it is diltributed through, or combined 

 with, the earthy, or perhaps other materials, is of great 

 confequence and importance, in fo far as it relates to the 

 nouriihment of the plants which grow upon them. The 

 above chemico-agricultural writer thinks, that where the 

 water is too ftrongly attrafted by the earths, it will not be 

 abforbed by the roots of the plants ; and that where it is in 

 too great quantity, or too loofely united to them, it will 

 tend to injure or dellroy the fibrous parts of the roots. In 

 his opinion there are two (fates in which water feems to exift 

 in the earths, and in animal and vegetable fubltances : in the 

 fird (late, it is conceived to be united by chemical, in the 

 other by cohefive attraftion. Tlie former of thefe is illuf- 

 trated by the pouring of pure folutions of ammonia or po- 

 tada into thofe of alum, when the alumine or alumina falls 

 down combined with water ; and the dry powder affording, 

 by didillation, more than half its weight of water. Alfo, 

 by the moilture which wood, mufcular libre, and gum, 

 that have been heated to 212', afford in the fame way at 

 a rrd beat, which is likewife water held m the fame 

 manner. 



Thi. latter is (hewn, it is fuppofed, when dried pipe-clay, 

 at the temperature of the atmofphcre, is brought into con- 

 tact with water, as the laft is rapidly abforbed. In general 

 too, foils, as well as vegetable and animal fubltances that 

 have been dried at a heat below tliat of boiling water, in- 

 creafe in weight by expofure to the air, in confequence of 

 their abforbing water from it, which is in the (late of vapour, 

 on account of this fort of attradlion. 



The water which is chemically combined among the prin- 

 cipal component parts of foils, unlcfs in the cafe of the de- 

 compofitiim of animal or vegetable fubltances, cannot, it is 

 fuppofed, be abforbed by the roots of plants ; but that 

 which adheres to the parts of the foil is in conilant ufe in 

 vegetation. Indeed, it ia believed that there are few earthy 

 mixtures met with in foils that contain any chemically com- 

 bined water ; water is expelled from the earths by moll lub- 

 ftances that combine with them. As for indance, when a 

 combination of lime and water is cxpof'd to carbonic acid, 

 that fluid fubdance takes the place of the water ; and com- 

 pounds of alumina and filica, or others of the earths, do not 

 chemically unite with water ; and foils, as has been feen, 

 are formed cither by earthy carbonates, or compounds of 

 pure earths and metallic oxyds. 

 8 



However, when faline fubftancee exid in foils, they may, 

 it is faid, be united to water, both chemically and mechani- 

 cally ; but they are always, it is fuppofed, in too fmall a 

 proportion to materially influence the relations of the foils 

 to water. 



The power or capability of the foil to abforb and receive 

 water, in confequence of this fort of attraction, depends 

 greatly upon the date of divifion of its parts ; as the finer 

 and more minute this is, the greater and more powerful is 

 the capacity for abforplion. The different conftituent parts 

 of foils feem likewife to operate, even by this kind of at- 

 traftion, with diflerent degrees of force and energy. In 

 this way vegetable fubflances feem, it is faid, to be more 

 abforbent than animal fubdances ; animal fubdances more 

 fo than compounds of alumina and filica ; and compounds of 

 alumina and filica more abforbent than carbonates of lime 

 and magnefia. Thefe difierences may, however, it is fug- 

 gefled, pofTibly depend upon the differences in their ilatej 

 of divifion, and on the furface which is expofed. 



This power or capability of foils to abforb water from the 

 air is, it is fuppofed, much connefted with fertility. The 

 foils which are the moll efficient in fupplyiag plants with 

 water, by means of atmofpheric abforption, are, it is faidi 

 thofe in which there is a due and proper mixture of fand» 

 finely divided clay, and carbonate of lime, with fome animal 

 and vegetable matter ; and which are fo loofe and light as 

 to be freely and readily permeable to the atmofphere. In fo 

 far as regards this quality, carbonate of lime, and animal and 

 vegetable matter, are, it is faid, of great ufe in foils. They 

 give abforbent power to them, without at the fame time 

 giving tenacity : fand, too, condantly dellioys tenacity, 

 but, on the contrary, adords little power of abforption. 

 The above writer has compared the abforbent powers of 

 many foils, in fo far as it relates to atmofpheric moifture, 

 and has condantly found it to be the greated in the mofl 

 fertile of them ; fo that it is fuppofed to afford one mode of 

 judging of the produftivenefs of land. 



Thus, the water, and the decompofing animal and vege- 

 table matter exifting in the foil, conflitute, it is fuppofed, 

 the true notirifhment of plants ; and that as the earthy parts 

 of the foil are ufeful in retaining water, fo as to fupply it in 

 the proper proportions to the roots of the vegetables, fo 

 they are likewife efficacious in producing the proper didri- 

 bution of the animal or vegetable matter. When equally 

 blended and intermixed with it, they alio prevent it from 

 decompofing in too rapid a manner ; and by their means the 

 folnble parts are fupplied in proper proportions or quantities. 

 But befides this agency, which may be confidered as me- 

 chanical, the writer conceives that there is another, between 

 foils and organizable matters, which may be regarded as 

 chemical in its nature. The earths, and even the earthy- 

 carbonates, have, it is faid, a certain degree of cliemical 

 attraftion for many of the principles of vegetable and animal 

 fubdances, as is readily exemplified in the cafe of alumina 

 and oil : for when an acid folution of alumina is mixed with 

 a folution of foap, which confid.^ of oily matter and potada, 

 the oil and the alumina will unite and form a white powder, 

 which will fink to the bottom of the fluid which holds it. 

 The extraft, too, from decompofing vegetable matter, when 

 boiled with pipe-clay or chalk, forms, it is faid, a combina- 

 tion by which the vegetable matter is rendered more difficult 

 of docompofition and folution. Pure filica and filiceous 

 fands have, it is remarked, little aftion of this kind ; and 

 the foil.j which contain the moll alumina and carbonate of 

 lime, are thofe which adl with the greateil chemical energy 

 in prcferving manures. Such foils are fuppofed to delerve 

 the appellation which is commonly given to them, of ricli 



foils : 



