carried over this
rear end by the grate in making the turn over the rear sprocket. In some
cases auxiliary dumping grates at the rear of the chain grates are used
with success.

Chain grate stokers in general produce less smoke than either overfeed
or underfeed types, due to the fact that there are no cleaning periods
necessary. Such periods occur with the latter types of stokers at
intervals depending upon the character of the fuel used and the rate of
combustion. With chain grate stokers the cleaning is continuous and
automatic, and no periods occur when smoke will necessarily be produced.

In the earlier forms, chain grates had an objectionable feature in that
the admission of large amounts of excess air at the rear of the furnace
through the grates was possible. This objection has been largely
overcome in recent models by the use of some such device as the bridge
wall water box and suitable dampers. A distinct advantage of chain
grates over other types is that they can be withdrawn from the furnace
for inspection or repairs without interfering in any way with the boiler
setting.

This class of stoker is particularly successful in burning low grades of
coal running high in ash and volatile matter which can only be burned
with difficulty on the other types. The cost of up-keep in a chain
grate, properly constructed and operated, is low in comparison with the
same cost for other stokers.

The Babcock & Wilcox chain grate is representative of this design of
stoker.

Smoke--The question of smoke and smokelessness in burning fuels has
recently become a very important factor of the problem of combustion.
Cities and communities throughout the country have passed ordinances
relative to the quantities of smoke that may be emitted from a stack,
and the failure of operators to live up to the requirements of such
ordinances, resulting as it does in fines and annoyance, has brought
their attention forcibly to the matter.

The whole question of smoke and smokelessness is to a large extent a
comparative one. There are any number of plants burning a wide variety
of fuels in ordinary hand-fired furnaces, in extension furnaces and on
automatic stokers that are operating under service conditions,
practically without smoke. It is safe to say, however, that no plant
will operate smokelessly under any and all conditions of service, nor is
there a plant in which the degree of smokelessness does not depend
largely upon the intellige