hitching and other posts, watering troughs, and drainpipe,
all successfully made of this useful material. In the barn, the barn
floor, the gutters, the manger and watering troughs, cooling tanks, and
sinks are also made of cement. While it is possible to differentiate
between the methods and the mixtures for these various purposes, it will
not be greatly in error if the construction always follows the following
principle.

Use enough cement to fill the voids in the gravel or in the sand and
stone mixture employed, and have enough sand in the gravel or with the
stone to fill the voids in the stone. This is readily determined, as
already suggested, by the use of water. The water, which will occupy the
voids in the stone, represents the necessary sand. When this amount of
sand and stone is well mixed, the water then permeating the interstices
represents the necessary cement, though it is a good plan to add about
10 per cent extra to allow for imperfect mixtures.

The mixing should always be done so thoroughly that when put together
dry, no variation can be seen in the color of the mixture. It is
surprising to see how readily a streak of unmixed dirt or of unmixed
cement can be detected in a pile by the difference in the color which it
presents. Such mixtures should always be made dry first and then the
water added and again mixed until the result is of a perfectly firm
consistency. Such a mixture can be applied to any of the purposes
mentioned, and, in general, it is better to have too much water than not
enough. The only difficulty with a very wet mixture is that the forms
require to be made nearly water-tight, whereas with dry mixtures the
same attention to the forms is not necessary.

If the concrete is to be used in thin layers, as in pipe or watering
trough, where a smooth surface is wanted, better results are usually
obtained by using a dry mixture and fine gravel and tamping the mixture
with unusual thoroughness. It is always unsafe to smooth up or
re-surface a piece of concrete. The difference in texture of the surface
coat causes it to expand and contract differently from the mass of
concrete underneath, and inevitably a separation occurs. If it is
desired to put on a sidewalk, for instance, a smooth top coat, the
consistency of the two kinds of concrete should be alike, and the top
coat should be applied almost immediately after the bottom layer is put
in place. Where concrete is used to hold water, a coat of