Steam:
Its Generation and Use

water inside the tubes, as it is heated, tends to rise towards the higher end, and as it is convert- ed into steam — the mingled column of steam and water being of less specific gravity than the solid water at the back end of the boiler—rises through the vertical passages into the drum above the tubes where the steam separates from the water and the latter flows back to the rear and down again through the tubes in a continuous circula- tion. As the passages are all large and free, this circulation is very rapid, sweeping away the steam as fast as formed, and supplying its place with water; absorbing the heat of the fire to the best advantage; causing a thor- ough commingling of the water through- out the boiler and a consequent equal temperature, and preventing, to a great degree, the formation of deposits or incrus- tations upon the heat- ing surfaces, sweep- ing them away and depositing them in the mud drum whence they are blown out. The steam is taken out at the top of the steam-drum near the back end of the boiler after it has thoroughly separated from the water. ADVANTAGES. The following are the prominent advan- tages which this boil- er presents over those of the ordinary con- struction : 1 .—Thin Heating Sur- face in Furnace. The thick plates nec- essarily used in ordi- nary boilers, in the furnace, or immediately ex- posed to the fire, not only hinder the transmis- sion of heat to the water, but admit of overheat- ing, and even burning the side next the fire, with consequent strains, resulting in loss of strength, cracks, and tendency to rupture. This is admit- tedly the direct cause of most explosions. Wat- er-tubes, however, admit of thin envelopes for the water next the fire, with such ready trans- mission of heat that even the fiercest fire cannot over-heat or injure the surface, as long as it is covered with water upon the other side. 2 .—Joints Removed from the Fire. Riveted joints with their consequent double thickness of metal, in parts exposed to the fire, give rise to serious difficulties. Being the weak- est parts of the structure, they concentrate upon themselves all strains of unequal expansion, giv- ing rise to frequent leaks, and not rarely to actual rupture. The joints between tubes and tube sheets also give much trouble when exposed to the direct fire, as in locomotive and tubular boilers. These difficulties are wholly overcome by the use of lap-welded water-tubes, with their joints removed from the fire. 3 .—Large Draught Area. This, which is limited in fire tubes to the actual area of the tubes, in this boiler is the whole chamber with- in which the tubes are enclosed, which, with down draft, gives ample time in the passage of the heat- ed gases to the chim- ney for thorough ab- sorption of theirheat. 4 .—Complete Com- bustion. The perfection of combustion depends upon a thorough mixture of the gases evolved from the burning of fuel with a proper quantity of atmospheric air; but this perfect mixture rarely occurs in or- dinary’ furnaces, as is proven by chemical analysis, and also by the escape of smoke, upon the introduction of any smoke- producing fuel. Even when smoke is not visible a large percentage of the com- bustible gases may be escaping into the chimney, in the form of carbonic oxide, or half-burnt carbon. Numerous attempts have been made to cure this evil, by admitting air to the furnace or flues, to “burn the smoke;” but though this may allow so much air to mingle with the smoke as to render it invisible, and at the same time ignite some of the lighter gases, it in reality does little to promote combustion, and the cooling effect of the air more than over- balances all the advantages resulting from the burning gas. The analysis of gases from va- rious furnaces shows almost uniformly an ex- cess of free oxygen, proving that sufficient air is admitted to the furnace, and that a more thorough and perfect mixing is needed. Every particle of gas evolved from the fuel should have