rendered by
a turbine-engine or other device for utilising the expansive power of
the gases which are driven from the constituents of the bones by the
action of the sulphuric acid.

For pumping water and other ordinary farm operations the chemical
gas-engine will prove very handy; and the great point in its favour
will be that instead of useless cinders the refuse from it will
consist of the most valuable compost with which the farmer can dress
the soil. Enamelled iron will be employed for the troughs in which the
bones and acid will be mixed, and a cover similar to that placed over
a "Papin's digester" will be clamped to the rim all round, the gases
being liberated only in the form of a jet used for driving machinery.

For very small motors, applicable specially to domestic purposes such
as ventilation, there is one source of power which, in all places
within the reticulation areas of waterworks, may be had practically
for nothing. Probably when the owners of water-supply works realise
that they have command of something which is of commercial value,
although hitherto unnoticed, they will arrange to sell not only the
water which they supply, but also the power which can be generated by
its escape when utilised and by the variations in the pressure from
hour to hour and even from minute to minute.

The latter, for such purposes as ventilation, for instance, will no
doubt come to the front sooner than the intermittent power now wasted
by the outflowing of water--a power which is comparatively too small
an item in most cases to compensate for the outlay and trouble of
arranging for the storage of energy. But in the case of the variation
in the pressure, without any escape of water at all, no such
disability appears. Experiments conducted in several of the larger
cities of England with various types of water meters--which are really
motors on a small scale--have proved the practicability of obtaining a
source of constant power from what may be termed the ebb and the flow
of pressure within the pipes of a water supply system.

At every hour of the day there is a marked variation in the quantity
of water that is being drawn away by consumers, and consequently a
rise and fall in the degree of pressure recorded by the meter. In an
apparatus for converting the power derivable from this source to
useful purposes something on a very small scale analogous to that
which has already been described in connection with utilising th