1S8 Mr. Majfey on Saltpetre. 
world, have been minutely defcribed, thefe de- 
fcriptions, through Tome defeCt or other, have 
been of little fervice to us, if we may judge 
from the many fruitlefs attempts to make this 
fait in England. 
The common accounts that are given us of 
nitre or faltpetre, are, indeed fo very vague and 
various, as rather to confufe and perplex, than 
give us any clear knowledge of it. Some will 
have it to be a production of nature , others en¬ 
tirely of art. Some tell us it is drawn from the 
air; others, that it is extracted from vegetables 
and animals. We are told too, that it is found 
upon the furface of the earth, and upon old walls 
in the form of hoar froft, and that whole pro¬ 
vinces are fometimes covered over with it; all 
which is certainly very falfe and fallacious; if, 
by faltpetre, in this place, is meant that faline 
concrete, which is of fo much ufe in the com- 
pofition above-mentioned; which, though fome¬ 
times found in the walks of nature, is molt 
afturedly, in general, a production of art. 
Saltpetre, to give a juft defcription of it, is 
a neutral faline concrete, evidently formed by 
a combination of a peculiar acid, with a fixt ve¬ 
getable alkaline fait. This acid is found in 
certain earths, from which it is extracted, by 
elixiviating them along with wood-afhes, the fixt 
fait of which, uniting with the acid, forms this 
neutraj 
