pains to leffen thefatnefs of their Land^ as other Na- 
tions do to encreafe the fatnefsof it. 
In Mechanics we have this account of it : If s faid by 
Pliny cap. de Vitri Inventione^ that a company of Mer- 
chants being thrown upon a fliore where there were not 
any ftones to be found, were forced to take great pieces 
of Egyptian Nitre out of their fliips, and make walls, 
upon which they hung their boyling Kettle, the Nitre be« 
ing heated by the fire, mixt with the fand, and ran into 
leveral ftreams of glafs, which afterwards hinted the way 
of making Glafs. It is likewife of ufe in Dying, for 
Tliny and Vitruvius a affirm, that by the help of this, the 
true Azure is made, and that without this, there cannot 
be a true fliadow. 
In the laft place I come to confider wherein it dif- 
fers frbmSalt Petre, and Sal Armoniac, it may be di« 
ftinguifhed from Salt Petre firft by its fermenting : it 
will ferment with any Acid , but Salt Petre will not : 
I found that it would ferment with Vinegar as the 
old Commentators obferve in their Comments upon 
Jeremiah and the Proverbs , but Salt Petre will not ; 
which gave occafion to fome, in thofe Texts, to alter 
the word Nitre. 
Secondly, it may be diftinguiflied from Salt Petre 
in its tafte, for Natron hath a lixivial taft, but the o- 
ther not. 
Thirdly, by the volatile Spirit which it affords : for 
from the one comes over a volatile Jlk^ly^ hm. from 
the other a corrofive Acid. 
Fourthly, the Natron aflFords a red clammy fubftance, 
infipid, but the other nots this clammy fubftance (if 
(aj de Archite^iura* Lib* j, 
E 2 Imiftake 
