26 Transactions. — Miscellaneous. 



accumulation of ash and small fuel, which would prevent a pi'oper sn]")ply of 

 oxygen to the rest of the fuel and to the evolved gases — the fire, therefore, 

 smoulders rather than barns ; and, secondly, wlien 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 tire, and tlien 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 eflfect 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 - - - - 1-26 

 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 



