s easily done. Sometimes it is
let down in great buckets closed at the top, but with a hinged bottom
that will open when the bucket strikes the rock or soil where the
material is to be left. Sometimes it is poured down through a tube.
Sometimes it is dropped in sacks made of cloth. This cloth must be
coarse, so that enough of the concrete will ooze through it to unite
the bag and its contents with what is below it and make a solid mass.
Sometimes even paper bags have been successfully used. The concrete,
made rather dry, is poured into the bags and they are slid down a
chute. The paper soon becomes soft and breaks, and lets the concrete
out. Sometimes concrete blocks are moulded on land and lowered by a
derrick, while a diver stands ready to see that they go into their
proper places.

Concrete is used for houses, churches, factories, walls, sidewalks,
steps, foundations, sewers, chimneys, piers, cellar bottoms, cisterns,
tunnels, and even bridges. In the country, it is used for silos, barn
floors, ice houses, bins for vegetables, box stalls for horses,
doghouses, henhouses, fence posts, and drinking-troughs. It is of very
great value in filling cavities in decaying trees. All the decayed
wood must be cut out, and some long nails driven from within the
cavity part-way toward the outside, so as to help hold the concrete.
Then it is poured in and allowed to harden. If the cavity is so large
that there is danger of the trunk's breaking, an iron pipe may be set
in to strengthen it. If this is encased in concrete, it will not rust.
A horizontal limb with a large cavity may be strengthened by bending a
piece of piping and running one part of it into the limb and the other
into the trunk, then filling the whole cavity with concrete. If the
bark is trimmed in such a way as to slant in toward the cavity, it
will sometimes grow entirely over it.

Concrete is also used for stucco work, that is, for plastering the
outside of buildings. If the building to be stuccoed is of brick or
stone, the only preparation needed is to clean it and wet it; then put
on the plaster between one and two inches thick. A wooden house must
first be covered with two thicknesses of roofing-paper, then by wire
lathing. The concrete will squeeze through the lathing and set. Stucco
work is nothing new, and if it is well done, it is lasting.

Concrete has been used for many purposes besides building, and the
number of purposes increases rapidly. For blackbo