Mr. MaJJey on Saltpetre . 199 
putrid and putrefiable fubftances into them— 
And in hovels ; by laying thefe materials in heaps 
.under them. The firft he difapproves, becaufe, 
as he tells us, though thefe walls are generally 
.covered with draw, the nitre, or rather the nitrous 
earth that is formed upon them, is frequently 
wallied away by the rain. But there is certainly 
.another obje&ion, and that is, the tedious time 
which thefe walls muft commonly ftand, except 
they are railed in the neighbourhood of dunghills, 
before they receive any considerable impregna¬ 
tion. In Pruffia, where we are told thefe walls 
2re raifed, by order of the king, throughout the 
.country, for the ufe of the faltpetre makers, we 
are at the fame time informed, they are often 
found but weakly impregnated, at the end of 
twenty years, though dung or litter is fometimes 
mixt up with the clay, of which they are 
compofed. 
He does not approve of difpofing the mate¬ 
rials in pits, becaufe, as he obferves, the air 
cannot be conveniently admitted to their inte¬ 
rior parts, )de, therefore, gives the preference 
to the difpcfal of them under hoyejs, where, by 
various contrivances that he lays down, the 
air may be freely admitted to them. And here 
we fhould certainly join him, could we be 
brought to believe tn^t a current of air, for 
which he contends, was any great promoter of 
putrefaftion. But we have been told, and have 
O 4 good 
