12 Elements of Mineralogy. 



founded; the affinities of Earths to acids 

 are generally known, but thofe of Earths to 

 each other and to calces of iron have no 

 where been treated of; and therefore require 

 fome developement. The efforts of art can 

 fcarcely exhibit in the humid way, the affini- 

 ties of Earths to each other, if this could be 

 effected, we mould probably find the fame 

 election and preference take place among 

 them as among Earths and acids, we are 

 therefore obliged to have recourfe to the dry 

 way, which is much more imperfect: foras they 

 are all reduced by fire to a ftate of liquidity, 

 they differ but little in fpecific gravity, and can 

 difficultly be examined while in fufion, when 

 cold they are all found fo mixed that it is 

 not poffible to judge of their affinities by the 

 way of preference and exclufion ; but if we 

 judge of thefe affinities as we do of that of 

 water to falts, by the greater or the leffer 

 quantity which one of them confidered as a 

 jnenftruum, can take up of another or what 

 proportion of the one deter mines the fufron of 

 another, we may in that manner form a tole- 

 rably accurate idea of their different attrac- 

 tive powers. 



Among the fimple Earths, the calcareous 

 alone,* can be looked upon as the menftru- 



* Perhaps the ponderous may alfo have th*is property, 

 but it being fcarce, no experiments have yet been made 

 with a view to determine this point. 



urn 



