1846.] Msorbent Po2vers of Earths. 317 



Marble and quick-lime, Mr. Leslie observes, produce nearly the 

 same effect, and in general no ditl'erence was observed between 

 the simple earths and their carbonates. The argillacious and si- 

 licious earths difler widely in their absorbent powers, but the cul- 

 tivated soils appear to possess this property in the highest degree. 

 Sea-sand, which gives only 40 deg., is by a few years' tillage, 

 capable of producing a dryness of 72 deg , and garden mould that 

 of 80 deg., an etiect not ascribable, as Mr. Leslie observes, to the 

 action ol manure, as the effect of this substance alone, when exa- 

 mined, was inferior to most of the earths. Speculating on these 

 facts, Mr. Leslie observes, that manures may peihaps be consi- 

 dered rather as stimulants in the process of vegetation; the atmo- 

 sphere may afford the carbonaceous matter or food of the plants, 

 whilst the earth affords expansion to the fibrils of the roots, and 

 supplies them M'ith the aqueous element. 



Torrification appears to diminish considerably the powers of 

 the earth to absorb humidity. Clay roasted in a strong fire, from 

 68 deg. gave only 35 deg. by the hygrometer, and being urged 

 by the heat of a blacksmith's forge, gave no more than 8 deg. 

 The same was observed with regard to whinstone, an effect which 

 cannot, Mr. Leslie says, be ascribed to an incipient vitrification, 

 for sandstone which had undergone violent ignition, shewed a 

 similar change of property. The affections of the simple earths 

 for moisture present some curious results. They are presented by 

 Mr. Leslie, as follows, the temperature at the time of observation 

 as before: 



Carbonate of strontian, - - 23 deg. 



Carbonate of barytes, - - 32 



Quartz, - - - - 40 



Marble, 70 



Carbonate of Magnesia, - - 75 



Alumine, - - - - - 84 



The great difference betw^een the dessicating power of strontian 

 and that of the other earths, is veiy singular, and affoids another 

 pioof, if such were wanting, of its being a distinct and indepen- 

 dent earth. 



It might be expected, that mixtures of the simple earths would 

 produce intermediate effects; which is not, however, the case. 

 Equal parts of silex and clay gave as much as the latter singly. 

 Bet the quantity of absorption must be distinguished from the 

 intensity. Strontian, barytes, and silex, are quickly saturated 

 with moisture, whilst magnesia and alumine continue to imbibe 

 it for a long time. Their effects in mixture depend on these 

 qualities combined, the alumine still attracting moisture after the 

 silex has ceased to act. 



