ASH-BALLS., 113 
set fire to it, gather up the ashes and form them 
into balls, which they then send to the next 
market-town, where they find ready customers in 
the shopkeepers and laundresses of the place. 
These balls are used as substitutes for soap in 
washing; two or three being melted in water and 
added to that in which the linen is washed. These 
balls are, in fact, a collection of the alkaline and 
other ingredients formerly existing in, and being 
part of the food of the fern plants. 
Thus, then, this interesting additional particu- 
lar about the food of the tree comes out. It 
requires certain chemical substances, besides those 
which it derives from the thin and viewless air. 
In the cases we have just mentioned, it is evident 
that the alkali potash, which enters into the 
formation of our common soaps, was a part of the 
food of the trees and plants from which, when 
they were consumed, it was obtained—from the 
reason of its being itself incombustible. In ad- 
dition to potash, the alkali soda and various other 
substances are now found to be actually necessary 
for the food ‘of plants. 
Many persons must have noticed the advertise- 
ments, in the different public papers, of different 
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