30 On the Analysis of Soils. 



certain extent, their composition, and serve as guides in 

 directing i!ie experiments. Thus, siUccous soils are gene- 

 rally rough to the touch, and scratch glass when rubbed 

 upon it; aluminous soils adliere strongly to the tongue, 

 and emit a strono- earthy smell when breathed on ; and cal- 

 careous soils arc soft, and much less adhesive than alumi- 

 nous soils. 



V. Mode of ascertaining the Qvantity of Water of 

 ylbsorption in Soils. 



Soils, though as dry as they can be made by continued 

 exposure to air, in all cases still contain a considerable 

 quantity of water, w hich adheres with great obstinacy to 

 the earths and animal and vegetable matter, and can only 

 be driven oft" from them by a considerable degree of heat. 

 The first process of analysis is, to free the given weight of 

 soil from as much of this water as possible, without, in 

 other respects, affecting its composition ; and this may be 

 done bv heating it for ten or twelve minutes over an Ar- 

 eand's lamp, in a bason of porcelain, to a temperature 

 equal to 300* Fahrenheit; and in case a thermometer is not 

 used, the proper decree may be easily ascertained, by keep- 

 ing a piece of wood in contact with the bottom of the dish : 

 as long as the colour of the wood remains unaltered, the 

 heat is not too high ; but when the w^ood begins to be 

 charred, the process must be stopped. A small quantity 

 of water will perhaps remain in the soil even after this 

 operation, but it always affords useful comparative results ; 

 and if a higlier temperature were employed, the vegetable 

 or animal matter would undergo decomposition, and in 

 consequence the experiment be wholly unsatisfactory. 



The loss of weight in the process should be carefully 

 noted ; and when in four hundred grains of soil it reaches 

 as high as 50, the soil may be considered as in the greatest 

 decree absorbent, and retentive of water, and will generally 

 be found to contain a large proportion of aluminous earth. 

 When the loss is only from '20 to ]0, the land may be con- 

 sidered as only slightly absorbent and retentive, and the sili- 

 ceous earth as most abundant. 



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

 Fibres from Soils. 



None of the loose stones, gravel, or large vegetable fibres 



• In several experiments, in which this process has been carried on by 

 distillation, I have found the water that came over pure, and no sensible 

 quantity of other volatile matter was produced. 



1 should 



