mass behind them, they are thrown off into the water by small stationary
fins or plows which are in such a position that they catch the pieces
nearest the edges and force them off as the plate revolves. This
arrangement, while allowing a free passage for the carbide, prevents an
excess from falling should the machine stop in any position.

When, as is usually the case, the feed mechanism is actuated by the rise
or fall of pressure in the generator or of the level of some part of the
gas holder, it must be built in such a way that the feeding remains
inoperative as long as the filling opening on the carbide holder remains
open.

The feed of carbide should always be shut off and controlled so that under
no condition can more gas be generated than could be cared for by the
relief valve provided. It is necessary also to have the feed mechanism at
least ten inches above the surface of the water so that the parts will
never become clogged with damp lime dust.

_Motor Feed._--The feed mechanism itself is usually operated by power
secured from a slowly falling weight which, through a cable, revolves a
drum. To this drum is attached suitable gearing for moving the feed parts
with sufficient power and in the way desired. This part, called the motor,
is controlled by two levers, one releasing a brake and allowing the motor
to operate the feed, the other locking the gearing so that no more carbide
will be dropped into the water. These levers are moved either by the
quantity of gas in the holder or by the pressure of the gas, depending on
the type of machine.

With a separate gas holder, such as used with low pressure systems, the
levers are operated by the rise and fall of the bell of the holder or