The Locomotive Of Today

The Boiler: Chimney, Formation of Scale. 27 exhausting device in conjunction with the escaping steam from the biast pipe, whereby the contents of the smokebox are withdrawn by virtue of its velocity, causing the draught already spoken of; and secondly, that the smoke, etc., may be carried away above the level of the driver and the train. It may be of cast iron, in one piece, as at D, built up of a cast top, pressed base, and connecting cone of plate, as E, or built up of plate entirely, as F. It has various external shapes, depending more or less upon individual fancy. We will now refer to the great difficulties to be contended with in the formation of deposit, and incrustation or scale in the boiler. When this is not more than the tliickness of an egg-shell where circulation is most active, it is no disadvantage, but is good rather than otherwise, as it forms a protection to the plates against the corrosive action of the water; but when it becomes thick enough to threaten the closing up of the water spaces, or gathers in large quantities on the tubes and plates exposed to g'reat heat, it causes a wasteful expenditure of fuel, tends to shorten the life of the boiler, and may become a source of danger. The heat from the firebox, when not carried off rapidly, as it should be by the fresh water brought to it by circulation, on account of the scale being a bad concluctor, overheats the plates, so that in course of time they may become burnt through. The formation of scale, when it gives rise to slight over- heating, causes unequal expansion, which is one of the principal sources of wear and tear in a boiler. Most waters used for locomotive boilers contain solid matters in solution, which are deposited by the high tempera- ture, or are left behind by evaporation. The first effect of the precipitation of these solids, unless cleaned out, will be to harden and form scale. There are usually from 20 to 40 grains of such matters to a gallon of ordinary water used for boilers, and it is easy to conceive what an excessive thickness would accumulate over the whole surface of the boiler below the water line if cleaning out be neglected for any length of time. It may be observed that the production of steam in a new locomotive boiler will increase at first, then remain stationary, and afterwards decrease. This may be, however, in part due to the elimination of priming, generally so great in new boilers, and which becomes less as the grease and dirt is removed. It has been stated that Tx^ of an in. of scale on the tubes is equivalent to a loss of 20 per cent, of fuel, and that the loss inereases in a very rapid ratio. Another observer has demon-