use apprehension. These occur from unequal settlement and other
causes. They should continue to be carefully grouted and faced until
settlement is complete.

The use of concrete is becoming more and more general for foundation
works. The desideratum hitherto has been a perfect and at the same
time an economical mixer. Concrete can be mixed by hand and the
materials well incorporated, but this is an expensive and man-killing
method, as the handling of the wet mass by the shovel is extremely
hard work, besides which the slowness of the method allows part of a
large batch to set before the other is mixed, so that small batches,
with attendant extra handling, are necessary to make a good job.
Mixers with a multiplicity of knives to toss the material have been
used, but with little economical success. Of simple conveyers, such as
a worm screw, little need be said; they are not mixers, and it seems a
positive waste of time to pass material through a machine when it
comes out in little better shape than it is put in. A box of the shape
of a barrel has been used, it being trunnioned at the sides. The
objection to this is that the material is thrown from side to side as
a mass, there being a waste of energy in throwing about the material
in mass without accomplishing an equivalent amount of mixing. Then a
rectangular box has been used, trunnioned at opposite corners; but
here the grave objection is that the concrete collects in the corners,
and after a few turns it requires cleaning out, the material so
sticking in the corners that it gets clogged up and ceases to mix.

The writer has just protected by letters patent a machine, in devising
which the following objects were borne in mind:

1st. That every motion of the machine should do some useful work.
Hitherto box or barrel mixers have gone on the principle of
throwing the material about indiscriminately, expecting that
somehow or other it would get mixed.

2d. That the sticking of the material anywhere within the mixer
should be obviated.

3d. That an easy discharge should be obtained.

4th. That the water should be introduced while the mixer
revolves.

With these desiderata in view, a box was designed which in half a turn
gathers the material, then spreads it, and throws it from one side to
the other at the same time that water is being introduced through a
hollow trunnion.

It is also so constructed that all the sides slope steeply toward