242 Superheaters by Boulton and Watt, and by Beardmore. In the case of the "Alhambra" and "Ceylon," the apparatus was fitted to the old boilers, so that the economy is unmistakably due to it alone, and one great advantage of this form of superheating apparatus is its great adaptability to existing boilers, as it can be fitted without any trouble, and occupies but little more space on the boilers than the chimney itself. Another advantage is that the flues offer little obstruction to the draught of the chimney, whereas in many cases in which tubes have been used, the draught has been so impaired from the passages having become choked with soot and ashes, that steam enough for the engines could not be obtained, which has necessitated the removal of the apparatus altogether. Figs. 247 and 248 represent the superheating apparatus introduced Fig. 247. tubes may be easily swept, by passing a brush through them, as is done in sweeping the tubes of ordinary tubular boilers. In the Holyhead packets, Messrs Boulton and Watt accomplish the superheating of the steam by a still simpler arrangement. The lower part of the chimney is surrounded by a steam casing, which is divided radially by six partitions, and the steam ascends through one of the divisions of the annular steam space and descends through another, receiving heat during its progress from the surface exposed to the smoke in the chimney. Figs. 249, 250, and 251 are representations of Beardmore's superheater as applied to an ordinary tubular boiler, fig. 249 being a longitudinal section of a tubular boiler with a superheater applied Fig. 249. by Messrs. Boulton, Watt, and Co. into the steamer "Great Eastern." In this case the smoke passes vertically through a number of small pipes set in a chest, and the steam which is let in at one side of the chest is drawn off at the other side, being heated in its transit by coming in contact with the heated pipes. The chest, in which the pipes are contained is placed over the root of the chimney, and the chimney is in point of fact a prolongation or continuation of that chest. One advantage of this arrangement is that the BEARDMORE'S SUTERHEATING APPARATUS. Longitudinal Section. to it, fig. 250 a transverse section, and fig. 251 a ground plan of the same boiler and superheater. This superheater consists of a box of horizontal tubes set in the root of the chimney, and the steam passes through the tubes and is heated by the smoke which ascends among the tubes and impinges on their external surfaces. The steam follows the direction of the arrows and is made to pass forward through one half of the tubes and back through the other half. This species of superheater has now been applied to many vessels with much success. It is found in practice that the tubes of the superheater do not require to be cleansed from soot, unless they are pitched closer together than them. In this superheater stop valves are not used, but the superheating tubes form an integral part of the boiler. JAFFREY'S SUPERHEATING APPARATUS OF CAST-IRON. Sons, of Durham; figs. 252, 253, and 254 being representations of one species of apparatus, and figs 255, 256, and 257 being representa |