[Footnote 33: In boilers constructed for stationary purposes, or for steam navigation, the steam-pipe, after it has passed through the blowing box, is continued and made to form a series of returned flues over the boiler, so as to take up the waste heat after it has passed the boiler, and before it reaches the chimney. But in locomotive engines for common roads, it has been found by experience, that the power gained by the waste heat is not sufficient to propel the weight of the material necessary for taking it up.]
So far as the removal of all inconvenience arising from noise, this contrivance has been proved by experience to be perfectly effectual.[34]
[Footnote 34: See Report of the Commons.]
In all boilers, the process of violent ebullition causes a state of agitation in the water, and a number of counter currents, by which, as the steam is disengaged from the surface of the water, it takes with it a considerable quantity of water in mechanical mixture. If this be carried through the cylinders, since it possesses none of the qualities of steam, and adds nothing to the power of the vapour with which it is combined, it causes an extensive waste of heat and water, and produces other injurious effects. In every boiler therefore, some means should be provided for the separation of the water thus suspended in the steam, before the steam is conducted to the cylinder. In ordinary plate boilers, the large space which remains above the surface of the water serves this purpose. The steam being there subject to no agitation or disturbance, the water mechanically suspended in it descends by its own gravity, and leaves pure steam in the upper part. In the small tubular boilers, this has been a matter, however, of greater difficulty. The contracted spaces in which the ebullition takes place, causes the water to be mixed with the steam in a greater quantity than could happen in common plate boilers: and the want of the same steam-room renders the separation of the water from the steam a matter of some difficulty. These inconveniences have been overcome by a succession of contrivances of great ingenuity. I have already described the rapid and regular circulation effected by the arrangement of the tubes. By this a regularity in the currents is established, which alone has a tendency to diminish the mixture of water with the steam. But in addition to this, a most effectual method of separation is provided in the vessel I, which is a strong iron cylinder of some magnitude, placed out of the immediate influence of the fire. A partial separation of the steam from the water takes place in the cylinder H; and the steam with the water mechanically suspended in it, technically called moist steam, rises into the _separator_ I. Here, being free from all agitation and currents, and being, in fact, quiescent, the particles of water fall to the bottom, while the pure steam remains at the top. This separator, therefore, serves all the purposes of the steam-room above the surface of the water in the large plate boilers. The dry steam is thus collected and ready for the supply of the engine through the tube N, while the water, which is disengaged from it, is collected at the bottom of the separator, and is conducted through the tube T to the lowest vessel D, to be again circulated through the boiler.