242 SOILS, MANURES, &c. 
filtrating paper, into a glafs or earth¬ 
en veffef, and add to it a few drops 
i 
of a ftrong folution of fixed vegetable 
alkali; this will immediately combine 
with, and neutralize the mineral acid, if 
there be any, and the earthy part will 
precipitate. 
On adding a little of the infufion of 
galls to the filtrated liquor, the quality 
of the acid may be afcertained ; if it 
contains iron, a blackilh recrement will 
precipitate, or grey if it contains copper. 
Some foils abound with metallic fub- 
fiances of the ferruginous kind, which 
make them appear of a rufty iron colour; 
thefe fubllances are frequently found 
confolidated with the foil, into large 
maffes, very ponderous and adhefive: 
earth of this quality is commonly called 
Foxbent, or Till; it is extremely unfa¬ 
vourable to vegetation. 
Upon 
