s8 ESSAYS AND OBSERVATIONS, 



ture to affirm ; but it appears to point 

 out a probable folution of the prefent 

 difficulty. To explain this in the moil 

 intelligible manner, it is neceiTary to ob- 

 icrve, iinq, That dry clay fuffi^rs a very 

 (ingular change from immerlion in wa-« 

 ter. For its particles, then gradually re- 

 ceding from niutual contact, come at 

 length entirely to lofe their cohelive power; 

 in confequence of which, the whole mafs, 

 after increafing in its volume, crumbles 

 down into powder. 2do^ That clay, by 

 the adlijn of fire, not only acquires a con* 

 fiderable degree of hardnefs, but is at the 

 fame time fo altered in its nature, that 

 the water can no longer make any ini • 

 prelhon on it. 3//5, I hat fand in its na- 

 tural rtate fuffers, from tha influence of 

 v/ater, no change as to the cohefion of 

 its particles ; and th;it it acquires no con- 

 fidcrable hardiicfs in the fire, ^to, That 

 calcarious earth, v/hen uncalcined, fuffers 

 as^ little change from water as fand does ; 

 but that, after calcination, it is affecl;e4 

 in the fune manner by that fiuid, as clay 

 is \n its natural ft ate. Thc'fe things Uq- 



