S46 
solution of oxide of iron in vinegar, and suffered 
it to remain in it till the leaves became yellow ; the 
roots were then carefully washed in distilled water, 
bruised, and boiled in a small quantity of the same 
fluid : the decoction of them passed through a filtre 
was examined by the test of infusion of nutgalls ; 
the decoction gained a strong tint of purple, which 
proves that solution of iron had been taken up by 
the vessels or pores in the roots. 
Vegetable and animal substances deposited in 
the soil, as is shown by universal experience, are 
consumed during the process of vegetation ; and 
they can only nourish the plant by affording solid 
matters capable of being dissolved by water, or 
gaseous substances capable of being absorbed by 
the fluids in the leaves of vegetables ; but such 
parts of them as are rendered gaseous, and that 
pass into the atmosphere, must produce a compa- 
ratively small effect, for gases soon become diffused 
through the mass of the surrounding air. The 
great object in the application of manure should 
be to make it afford as much soluble matter as 
possible to the roots of the plant : and that in a 
slow and gradual manner, so that it may be en- 
tirely consumed in forming its sap and organized 
parts. 
Mucilaginous, gelatinous, saccharine, oily, and 
extractive fluids, and solution of carbonic acid in 
water, are substances that in their unchanged 
states contain almost all the principles necessary 
for the life of plants ; but there are few cases in 
which they can be applied as manures, in their pure 
forms ; and vegetable manures, in general, contain 
