24 APPENDIX. 



Portugal, Spain, and elsewhere ; and although no shot has yet penetrated a boiler, the paddle- 

 boxes and other parts have borne strong testimony of the risk to which they are liable. 



The increase of expense to effect all suggested, is not worth mentioning as an item in the 

 value of a steam-engine. 



To illustrate the construction of marine boilers those of the ' Medea' and 'African' steam 

 ships are represented in Plate xxn. 



REMARKS ON ATLANTIC STEAM NAVIGATION. 



33. In Atlantic steam navigation the fullest effect should be brought out with the engines 

 and boilers as now constructed, the necessities being greater than that of any other effort of 

 steam as a propeller. 



WASTE OF FUEL FROM CYLINDERS. I have alluded to the advantages of non- 

 conductors ; this should be carried as far as possible in these ships. Cylinders, slide casings, 

 as well as boilers, should be completely incased. The following facts will remove all question 

 of the propriety. 



In the ' African ' the cylinders are about 5 feet 3 inches distant from the boilers : there 

 are no hatches immediately over them, and the short steam-pipes are covered with fear- 

 nought, &c. The quantity of distilled water produced from the belts of 50 feet square surface 

 which girt the cylinders (there are no jackets surrounding them) in the Mediterranean, was 

 constantly about 270 gallons in 24 hours ; that is, a quantity of fuel was lost by radiation 

 from the belts of the cylinders in 24 hours, equal to that which would raise 270 gallons of 

 water, at a boiling temperature, into steam. 1 



From experiments made on board the 'African' in December, 1831, moored in still 

 water, without the influence of tides, 306 cubic feet of fresh water (measured) were required 

 to maintain the engines at an uniform velocity of 12 revolutions per minute for 6 hours, 

 at an expense of 24 cwt. of Heaton Main coal ; one boiler or two furnaces only being 

 employed ; a certain portion of heat being abstracted by the joining boiler, which was in all 

 respects distinct from that employed : now 270 gallons = about 44 cubic feet of water pro- 

 duced in 24 hours from the belts of the cylinders; and 306 cubic feet x 4 == 1224 cubic feet 

 of water evaporated in 24 hours by 24 cwt. x 4 = 96 cwt. of coals, according to the 

 experiment above noted. 



Hence 96 cwt. x 44 cubic feet = 3 . 45 f coa , s &s ft dead 



1224 cubic feet 

 required in 24 hours to maintain the temperature of the belts alone. 



Here the tops and other portions of two cylinders of 38 inches in diameter only, and slide 

 casings, are not at all taken into consideration. The loss here recorded is rather under than 

 over rated. The water thus procured was constantly appropriated to the use of passengers 

 and the ship's company ; and, when on the Alexandrian station, no other water was made use 

 of in the ship, 10 tons only excepted, being the greatest quantity received at Malta, the 

 absence from which port being never less than 18 days. 



In the steam frigates, the quantity of distilled water produced at sea in 24 hours, by the 



1 The steam pipes, although covered, no doubt contributed in some measure to the loss above stated. 



