22 ESSAYS AND CBSEKYAilONS 



carried away by the water in the procefs 

 of elutriation. 



It may be here obferved, that the effer- 

 Tefcence enfuing upon the application of 

 acids to marie, cannot be relied upon as 

 a certain indication of the quantity of 

 ealcarious earth contained in fuch fub- 

 ftances. Numerous inflances of the truth 

 of this aflertion have occurred to me. For 

 the eiFervefcence varies, both in violence 

 and duration, according to the flrength 

 of the acid employed ; but it varies flill 

 more accordmg to the penetrability and' 

 other more fecret circumitances of the 

 <alcarious bodies. 



6 E CT. vr. 



I next examined what eflfedls fire Would 

 jjroduce upon marie in its natural ftate. 

 As many marles contain a very confider- 

 able proportion of ealcarious earth, I ex'- 

 pedled that nearly the fame changes 

 would be produced upon them by calci^ 

 ]ftation,as upon limeftone. 



EX-PER.. 



