18 *fl>6 Principles of Part I. 



clay grounds are fo apt to cake with heat, 

 especially if they have been ploughed wet, 

 and will, in that flate, hinder the roots 

 of vegetables from paffing through them. 



THE SE qualities of clay feem to depend 

 on the fame caufe, viz. the ftrong adhefive 

 power of its particles. Its great ductility 

 fhows, that its particles adhere very firmly. 

 But whence this adhefion ? Is it from a 

 certain figure of its particles, by which 

 they are intangled, and can it be fo eafily 

 feparated ? or is it from oleaginous particles 

 mixed with the earthy, as we know that 

 oil is adhefive, and rejects water ? I incline 

 to the latter opinion, as I have found that 

 clay contains an oil, not fo loofe indeed 

 as in the former foil, but intimately con- 

 nected with its earth, and fcarcely fepara- 

 ble from it. 



Exf. 4. I mixed forne clay with vinegar; 

 but there was no fermentation, and the acid 

 tafte was not blunted. It feems then to 



have 



