234 SOILS, MANURES, &c. 
\ 
the only fpecies of acid that can anfwer 
the grand purpofes of vegetation; they 
become reciprocally neutralized with it, 
but are Hill capable of uniting and incor¬ 
porating with the oleaginous particles of 
the earth, and by the addition of air and 
water, become attenuated, conco&ed, and 
matured, forming altogether the fapo- 
naceous mucilage, which is allowed to 
be the effential pabulum, or nutriment 
of plants. 
From thefe fadts, it may be ealily 
deduced, that no fubftance ought to be 
i 
e(teemed eligible as a manure, which 
does not contain fome proportion of 
alkaline falts. 
All animal, and fome vegetable fub- 
ftances, afford volatile alkaline falts and 
oil, in a greater or fmaller degree ; and 
as dung, which is eafy to procure, par¬ 
takes of all thefe qualities, fo is it princi- 
