BOILERS FOR STATIONARY ENGINES.

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is formed in the flues, for if the gases are not consumed before reach-ing the flues, it is impossible to burn the smoke with the ordinaryarrangements; but those who are under the impression that smoke,or at least what we term smoke, cannot be burned when once formed,labour under a sad mistake, for the densest volume passing througha regenerative furnace is effectually consumed.

We will take the Butterly boiler, having two internal flues or fur-naces meeting in one combustion chamber at the back of the bridge:fire both of these furnaces at one and the same time,- and densevolumes of smoke will be seen issuing from the top of the chimney;the smoke is formed in the furnace, and passes over the bridge.Now this arrangement, with careful firing, in a great measure preventssmoke issuing from the chimney. One fire should be bright whilethe other one is dull, or in the act of firing, and what is the conse-quence? the combustion chamber is in a perfect glow, from the brightfire; and the smoke evolved by the dull one is effectually consumedby the other. This simple fact is half of the battle; careful firingis the best and most economical means for the prevention of smoke;so by alternately firing little or no smoke is seen issuing from thetop of the chimney. Such practice every good fireman is perfectlyconversant with.

As hydrogen is the main element in the gases evolved, and bythe admixture of the oxygen of the atmosphere flame is produced;and as neither hydrogen nor oxygen can bum of itself, it remains forus to supply a current of air, so as to obtain the most economicalresult from the fuel. With the common blow-pipe an intense heatis obtained by simply blowing a current of air through a flame ofgas, or rushes, as used by the gasfitter. And in the smelting fur-nace air is forcibly blown through a coil of pipes, surrounded andinclosed in a furnace, the air is thus intensely heated, and, indeed,will melt a bar of lead before it is admitted into the smelting fur-nace; this is termed the “hot bläst” and is familiär to all metallur-gists. Were it not for the complication entailed, this method wouldbe by far the best plan that could be adopted for steam boilers, butsuch an intense heat is not at all desirable, for should the water inthe boiler fall below the working level, the plates would get intenselyhot, and an explosion would be the inevitable result; so a moderatemeasure of heated air is all that is required.

A very simple plan for introducing heated air is by arrangingsmall pipes, fixed to the front plate of the boiler, as in the double