SOILS, MANURES, &c. 261 
A fufficient expofure of cold, hard, 
fpring water, containing metallic fub- 
fiances, to the fun in fummer, caufes it 
to be lefs chilling to the earth, renders 
it rather fofter, and lefs pernicious to 
plants: if it be long expofed, fome 
of its pureft particles will, of courfe, 
exhale ; but at the fame time the mine¬ 
ral acid will alfo gradually fly off, which 
is the principal caufe of its hardnefs ; 
the metal will fall to the bottom, being 
feparated from its acid, and the water 
will confequently become confiderably 
improved by fuch expofure. 
Snow is an excellent prefervative to 
plants againft froft, and, when not too 
deep, it admits light and air freely. 
Froft is as deftru£live to tender plants 
as it is beneficial to the foil; it .a£ls 
principally on their fluids, which dilate 
and expand as they congeal, and fhoot 
like 
