26 Transactions.— Miscellaneous. 
accumulation of ash and small fuel, which would prevent a proper supply of 
oxygen to the rest of the fuel and to the evolved gases—the fire, therefore, 
smoulders rather than burns; and, secondly, when the fire is stirred (and also 
when fresh fuel is added) a certain amount of the burning fuel is broken and falls 
through the bars to waste, and if the fire-bars are placed nearer to each other, 
with a view to prevent the fuel passing through them, so much more will the 
draught be impeded. Another evil arising from the stoppage of air through the 
fire will be that unburnt gases and smoke pass up the chimney. Now, if these 
sources of waste were removed, there would, of course, be the same quantity of 
heat evolved from the 1} tons of Green Island coal as from the ton of 
Newcastle coal ; but considerably more time would be required, first in getting 
up the fire, and then in consuming it, which is a serious drawback to its use 
for steam purposes, and determines the use of Newcastle and other coals even 
in those places where the brown coals may be said to be at our very doors. 
It becomes a matter of importance, therefore, to consider whether a special 
construction of furnace could be devised in which the ashes are removed as 
soon as formed from all parts of the glowing fire, and all the evolved gases 
which are capable of uniting with the oxygen of the air thoroughly oxidized, 
while, at the same time, such a degree of intensity may be imparted to the 
combustion as to render it available for the generation of steam with the 
rapidity requisite for marine boilers and locomotives. 
To effect this, I propose to do away with the fire-bars, and to use a certain 
fraction of the heat force of the furnace (when changed into its equivalent 
motive force), so that it shall send a gentle blast of air upwards through all 
parts of the fuel, and thence through a great number of small and thin copper 
tubes of the boiler till it reaches the smoke box. It now becomes necessary, 
before proceeding further, to consider the relative specific gravities of the 
contents of the furnace after the fire has been kindled some time and the blast 
in operation ; and there is this remarkable property which must have struck 
everyone that has used these brown coals, with regard to their ashes, namely, 
their extreme lightness and the ease with which they are reduced to an 
impalpable powder. 
Specific gravity of Clutha coal «e ж d DEM 
Specific gravity of its ash flake - - - - 0°04 
The ash is therefore about thirty times lighter than the fuel, and twenty times 
lighter even when the volatile gases are driven off from it. It is important 
that these bulky ashes be removed, not only from the bottom of the furnace, 
but from every part of the glowing fuel, for dust would not be more 
obstructive to the proper action of the human lungs than accumulations of ash 
to that of a furnace. The difference between the specific gravities of coal and 
its ash flake allows, therefore, of its removal as fast as it is formed, while the 
