OF FOSSILS. 147 



earth, faturatcd with the nirrous acid is treated 

 in a fimilar manner: Therefore it fccms rather 

 to refcmble a metallic ealx than an earth, by 

 thcfc properties. 



Among tiie metallic calces, that which arifes 

 from load corrcfponds with the ponderous earth 

 in its weight, its white colour, and peculiar at- 

 traction for the vitriolic acid, by which that a- 

 cid is torn away from alkaline falts ; but there 

 is notwithilnnding a remarkable difference be- 

 tween them. Acctatcd lead is diihirbed wholly 

 in the cold by phlogiflicatcd alkali, anddepofits 

 a fediment, which neither is folublc in water, nor 

 in the vitriolic ncid ; but theacctatcd ponderous 

 earth yields its genuine precipitate by heat on- 

 Jy, and which is folublc both in the vitriolic a- 

 cid and in boiling water. Bcfidcs, this earth 

 has hitlierto refilled all efforts to reduce it to 

 a mefallic (late. 



Therefore, although there may appear a con- 

 fidcrable affinity between the ponderous earth 

 and a metallic calx ; yet, as long as it is incapa- 

 ble of reduction, its metallic nature is certainly 

 nut fullicicntly demon (Ira ted, and it mull ilill 

 retain a place among tlic earths. 



LXXVII. Five Genera JJwnhl be eonjlituted of 

 the five primitive Earths. 



As we have enumerated already five primi- 

 tive earths, they naturally become the heads of 

 < five 



