_Soil Blending._--"As it may sometimes happen that earth of a proper
quality is not to be found on the spot where it is intended to build, it
becomes of importance to attend to the method of mixing earths; for
though the earth which is near at hand may not of itself be proper, it
is very probable that it may be rendered so by the mixture of a small
quantity of another earth fetched from a distance. The principle on
which a mixture must be made is very simple; strong earths must be
tempered with light; those in which clay predominates, with others that
are composed more of chalk and sand; and those of a rich, glutinous
substance, with others of a poor and barren nature. The degree in which
these qualities of the earths prevail must determine the proportions of
the mixture; which it is impossible here to point out for every
particular case, but which may be learnt by a little practice. Some easy
methods will be described, by which any one may make a trial of the
qualities of his earth.
"It will not be amiss to mix with the earth some small pebbles, gravel,
rubbish of mortar, or in short any small mineral substances; but none of
the animal or vegetable kind must be admitted.[5] Such hard substances
bind the earth firmly between them, and being pressed and pressing in
all directions, contribute very much to the solidity of the whole; so
that well-worked earth, in which there is a mixture of gravel, becomes
so hard at the end of two years that a chisel must be used to break it,
as if it was freestone."
[Footnote 5: "The pise does not admit any vegetable or animal
substances. In mud walls they put straw, chopped hay, hair,
flocks, wool, etc., to make the mud adhere to the wood, or laths;
whereas the workmen who build in pise are careful to pick out the
least straw or the smallest bit of root which remains in the
earth: in short, the pise is a mineral substance imitating stone,
consequently anything that can slake or rot must be excluded."]
[Headnote: Experiments]