THE SMOKE ABATEMENT EXHIBITION. 
239 
* In Chubb’s atmospheric blast means are devised to open or 
shut, by means of levers worked at the front of the furnace, 
certain openings at the back of the furnace for admitting air 
through the bridge to the unburnt gases. The air is drawn in 
owing to the difference in temperature between the furnace and 
the ash-pit, and in passing through the bridge becomes intensely 
heated. 
Hunter’s Smoke Consumer is interesting on account of the 
mechanical contrivances it contains. The furnace is hand fired. 
Each time firing takes place, and by the opening of the furnace 
door, an opening is made by which air passes to the bridge. 
This opening is kept from closing by a valve which contains 
mercury. This takes some time to flow through a hole, and 
until it has flowed away the opening will not shut. Thus air is 
admitted to the bridge, and escapes through perforations in it for 
a certain time, which can be regulated at will, after the furnace 
doors have been closed. 
A very convenient form of furnace front and firedoor is shewn 
by Mr. Thomas Henderson, of Liverpool. It has been largely 
used in marine boilers. It consists of a V-shaped casting, 
which serves as furnace door and dead plate, connected across by 
a perforated plate, which serves to admit air to the furnace. It 
is balanced by a spring, to prevent it from falling down. The 
length of the two parts of the V-piece is the same. To use it, 
the fireman pushes the door inwards. The door then serves as 
a dead plate, while stoking is going on. After stoking, the plate 
is restored to its old position, but for cleaning out, the door is 
pushed still further down, and a vacant space is left for the 
clinker to pass down, whilst, at the same time, the hot gases 
from the clinker pass through the vacant space to the furnace, 
and thence to the chimney, and the heat from the ashes is pre- 
vented from reaching the legs of the stokers by the door which, 
in this position, is interposed between them. 
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