Steam:
Its Generation and Use

work after sixteen to twenty years, but most of them have been altered to the later type. Nos. 8 and 9 are what were known as the Griffith & Wundrum boilers, afterwards merged improvement in action over No. 9. The four passages of the gases did not add to the economy in either Nos. 8, 9 or 10. into the Babcock & Wilcox. In these, ex- periments were made on four passages of the gases across the tubes, and the down- ward circulation of the water at the rear end the furnace before being delivered into the drum above. The tendency was as in all similar boilers, to form steam in the middle of the coil and blow the water out from each end, leaving of the boiler was carried to the bottom row of tubes. In No. 9, an attempt was made to reduce the amount of steam and water capacity, increase the safety and reduce the cost. A drum at right angle to the line of tubes was tried, but found to be insufficient to secure dry steam or regularity of action. The changes were not found to possess any advantages. No. 10.—A move in the same direc- tion. A nest of small horizontal drums, 15 in. in diameter were used instead of the single drums of larger diameter; and a set of circulation tubes were placed at an intermediate angle, between the main bank of heating tubes and the horizontal the tubes practically dry until the steam found an outlet and the water returned. This boiler not only had a defective circulation but a decidedly geyser-like action, and produced wet steam. All the above types, with the exception of tubes which formed the steam reservoir, to return the water carried up by the circulation to the rear end of the heating tubes, allowing the steam only to be delivered into the small drums above. The result was exceedingly wet steam, with no Nos. 5 and 6, had a large number of bolted joints between their several parts and many of them leaked seriously, from unequal expansion, as soon as the heating surfaces became scaled ; enough boilers having been placed at work