EXPLANATION OF THE PLATES. 355 



PLATE XXII. 



BOILERS OF H.M. STEAM VESSEL " AFRICAN." 

 See the description of the next plate. 



PLATE XXIII. 



BOILERS OP H.M. STEAM FRIGATE " MEDEA." 



This and the preceding plate are also furnished by Mr. Dinnen in connexion with 

 his paper in the Appendix on steam boilers. The following is his description. 



(The same letters refer to corresponding parts in the several views.) 

 a, Furnaces. 



a, Grate bars. 

 a", Bearer bars. 



b, Ash pits. 



c, Bridges. 



d, Flues. 



e, Smoke-joints,! ., 



/ Oi . . > tor connecting the fore with the after boilers. 

 e , Steam-joints, j 



/, Uptake, through which the smoke, &c., passes from the flues to the chimney. 



ff, Chimney. 



h, Air casing, which surrounds the base of the chimney to prevent too great a trans- 

 mission of heat to the deck, or other materials liable to be injured thereby. 



z, Dampers with their levers, for checking the draught of the furnaces. 



j, Water ways between the flues and fireplaces. 



/, Water ways of the bridges, and beneath the flues and fire-places, such that one 

 may enter at the mud hole doors, forward and aft, and pass over the entire 

 bottoms of the boilers, and under the flues. 



k, Mud hole doors, with a similar one on each after boiler. 



/, Furnace doors. 



m, Clinker bars, for supporting the levers employed in clearing the furnace bars. 



n, Feed pipe, with two branches and valve boxes, for supplying the boilers with 

 water. 



