Chap. 9.] [ 47 1 



CHAP. IX. 



EARTHS IN GENERAL. 



Different Kinds of Earth. -Nevj Earths difco*vered Definition r,f 

 Earths. Exceptions. Other general Properties of Earths. Ca/ca- 

 reeus Earth . Magnefia . Earytss. Clay . Flint. 



IT is now generally agreed among chemills and 

 mineralogifts, that all the earthy and ftony fub- 

 ftances which compofe the folid parts of this globe, 

 are chiefly refolvable into five fimple and original 

 kinds of earth ; namely, lime or calcareous earth, mag- 

 nefia, barytes or ponderous earth, argill or clay, and 

 filica or flint; to thefe late difcoveries have added three 

 other earths, the ftronthian, the jargonic, and the ada- 

 mantine; but thefe are found in very fmall quantities, 

 and doubts are yet entertained whether they are any 

 thing more than varieties or compounds of the five 

 principal earths. 



Thefe fubftances agree in the following proper- 

 ties, which may be confidered as the .characlreriftics 

 of all earthy fubftances. They are nearly infolu- 

 ble in water, are uninflammable, have not the metallic 

 fplendour, and their fpecific gravity, compared with 

 that of water, is not more than five to one. This 

 definition, however, like that of falts, is not fo pre- 

 cife as to be beyond the reach of criticifm ; becaufe 

 there are fome earths perfectly foluble. in water, though 

 but in fmall proportions, and there are many in the 

 internal parts of the earth which afford the -flrongeft 

 evidence that they havr been in a (late of folution. 

 But the definition, though not ftriftly accurate, is pro- 

 per in a general fenfe. There is great difference of 

 iblubility between earths and fairs, for a few grains of 



earth 



