201 
Mr. Maffey on Saltpetre . 
lower, and the want of moifture, which cannot 
eafily be introduced to fuch lofty heaps. 
About thirty years ago, an ingenious Chemift, 
of our own nation, having vifited many of the 
oreat works abroad, and made the obfervation, 
that to form a nitrous earth, nothing more ap¬ 
peared to be neceffary, than to mix up calcareous 
earths with any kind of dung, and expofe thefe 
materials to the air, returned home, fully per- 
fuaded that he was mafter of the fecret, and had 
intereft enough to prevail upon many of his 
friends to join him, in erecting a large faltpetre 
work, at Fulham, near London. Here, many 
hundred loads of lime were got together, and 
laid with ftrata of horfe muck, in long high 
ridges, the more to be expofed to this element; 
the confequence of which was, that the rain run¬ 
ning off, without penetrating the mafs, no putre¬ 
faction enfued, and the lime, at the end of four 
or five years, was found to have received little or 
no impregnation; upon which the work was 
dropped, with great lofs to the Proprietors. 
Two errors were here committed. In the fir ft 
place, the dung, which ought to have been, at 
lead:, in treble the proportion to the lime, made 
but about one fourth part of the heaps. And 
fecondly, they were fo difpofed, that, for 'want 
of moifture, they could never enter into a putrid 
fiate: whereas, had the dung been in a due pro¬ 
portion, and the whole been fp'read about a yard 
thick, 
