ANALYSIS OF SOILS. 



8.5 



V. Mode of ascertaining the Quantity of Water of Ahforption 

 in Soils. 



Soils, though as dry as they can be made by continued ex- Evaporation of 

 pofure to air, in all cafes ilill contain a confiderable quantity the airbed 

 of water, which adheres with great obflinacy to the earths and j ts quantity in* 

 animal and vegetable matter, and can only be driven ofFfrom foils, 

 them by a confiderable degree of heat. The firft procefs of 

 analyfis is, to free the given weight of foil from as much of 

 this water as poffible, without in other refpecls, affecting its 

 compofition; and this maybe done by heating it for ten or 

 twelve minutes over an Argand's lamp, in a bafon of porce- 

 lain, to a temperature equal to 300 * Fahrenheit ; and in cafe 

 a thermometer is not ufed, the proper degree may be eafily 

 afcertained, by keeping a piece of wood in contact with the 

 bottom of the dim ; as long as the colour of the wood remains 

 unallered, the heat is not too high; but when the wood begins 

 to be charred, the procefs mutt be (topped, A fmal] quantity 

 of water will perhaps remajn in the foil even after this opera- 

 tion, but it always affords ufeful comparative refulls j and if a 

 higher temperature were employed, the vegetable or animal 

 matter would undergo decompofition, and in confequence the 

 experiment be wholly unfatisfactory. 



The lofs of weight in the procefs lliould be carefully noted, One- eighth is 

 and when in four hundred grains of foil it reaches as high as an extreme pro- 

 50, the foil may be confidered as in the greateft degree abfor- P ° r 10n * 

 bent, and retentive of water, and will generally be found to 

 contain a large proportion of aluminous earth. When the lofs 

 is only from 20 to 10, the land may be confidered as only 

 ilightly abforbent and retentive, and the filicious earth as moll 

 abundant. 



VI. Of the Separation of Stones, Gravel, and vegetable Fibres 

 from Soils. 



None of the Ioofe ftones, gravel, or large vegetable fibres Stones, &c. to 

 fliould be divided from the pure foil till after the water is drawn be fe P aratt ? a &- 

 off; for thefe bodies are themfelves often highly abforbent and & c . 

 retentive, and in confequence influence the fertility of the land. 



* In feveral experiments, in which this procefs has been carried 

 on by diftillation, I have found the water that came over pure, and 

 no feniible quantity of other volatile matter was produced. 



The 



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