[ 6o J 
this property, but in a lefs degree,' which may be 
owing to their not being perfedly free from other 
falts. 
It may be doubted whether the mineral alkali be 
not generated upon the Pic, where it is found, by the- - 
litnefs of that fort of earth to attract out of the air 
fome of the principles, of which it is made : for there; 
is often feen upon walls a faline efflorefcence, which 
proves to be this very faltj and fome earth, as that 
at the bottom of a lake in Egypt, is faid to produce 
it, fo as to make a conftant lupply of a great quan- 
tity, which is every year dug up and carried away. 
The natron mufl be in great abundance in the air or 
earth, as it is the bafe of that fait, which is the 
commoneft of all in almoft every part of the world ; 
but though it be every where found, when united 
to the acid of fea-lalt, yet there are but very few 
es, where we have been able to procure it ^ 
IX. Shcrl 
