ON ATLANTIC STEAM NAVIGATION. 25 



jackets of the cylinders, of 162 feet square surface, amounts to upwards of 4 tons! equal to 



143-36 cubic feet. 



Now, according to the foregoing, 



143-36 cubic feet x 96 cwt. = n>24 cwt> of coalg in 24 hourS; to meef . the radiation of heat 

 1224 cubic feet 



from the jackets of the cylinders ; and when they are placed forward, and at a considerable 



distance from the boilers, the expense is much greater. 



The saving of fuel and comfort in the engine-room would be, on the whole, very con- 

 siderable, particularly in 400 horse engines, were the loss, before estimated, prevented by 

 clothing. 



34. WASTE OF HEAT FROM BOILER. As to the waste of heat from the boilers, from 

 experiments I made in the coal-boxes, I found that when the thermometer ranged from 50 

 to 59 on deck during five days, it increased to 116 in the boxes, the thermometer being 

 suspended from the beams in the neighbourhood of scuttles, which were left open more or 

 less night and day, and through which the heated air was constantly escaping from the 

 coal-boxes ; this heat was radiated through a space of 6 or 7 inches, at which the coal-boxes 

 were distant from the boilers, a large hatch directly over the boilers being at the same time 

 kept open for ventilation. The thermometer, when the bulb was applied to the coal-box 

 plates, two-thirds of their depth from the deck, varied from 138 to 148 ; and when applied 

 to the front plates of the boilers, the temperature indicated was 169, not very greatly 

 exceeding that of the coal-box plates. 



One important fact was elicited on these experiments, that when the surface of the coals 

 was removed, and the thermometer introduced amongst the lower portion, it was raised 36 

 above the temperature of the air in the boxes, vapour being given out from the surface 

 exposed ; that coal which was immediately in contact with the coal-box plates appearing as if 

 dry distilled. From this I was led to judge, that the lower portion of the coal being pressed 

 upon by the superincumbent mass, and constantly receiving heat from the moment of getting 

 the steam up, maintained this heat embodied in the form of vapour ; which, not being able 

 to escape through the mass, assisted in extracting the gaseous portion of the coal, tending to 

 produce spontaneous combustion ; which I have witnessed in several instances, although these 

 consequences are mostly found to be brought about by defective smoke-joints. The injurious 

 effect of this heat on the constitution of the coal trimmers, and the great amount of fuel 

 wasted by this channel, clearly demand every attention from those interested in the Atlantic 

 voyage. 



From the data furnished by the loss of fuel from the jackets of the cylinders, all other 

 circumstances being the same, an approximation may be arrived at of the waste by radiation 

 from the boilers ; thus, the entire external surface of the boilers and steam-chests of the 

 ' African ' amounts to 855 feet square ; and the area of the belts being 50 feet square, effecting 



a loss of 3-45 cwt. of coals per day, we have, 3 ' 45 cwt ' x ** 5 sq " ft ' = 58-99 cwt., or 2-95 



50 sq. it. 



tons of coals required in 24 hours to meet the loss from radiation in these comparatively small 

 boilers : in this calculation, the surface of the bottoms of the boilers is included ; the loss 

 from which, it should be observed, is trifling when shielded, by platforms, from exposure to the 

 bilge water. 



d 



