AND SURFACE CONDENSEK. 351 



another tube, 2 inches more in diameter, giving a space 

 into which the used steam from the cylinder passed to be 

 condensed. Then came the outside tube, 2 inches more 

 in diameter, forming a second space for the passage of 

 air, taking heat from the condenser into the fire. The 

 steam-boiler had its heat retained by a coating of 

 charcoal ; next to it came a current of cold air an inch 

 thick, carrying back to the fire any heat that had 

 passed through the charcoal coat, and also the heat 

 from the inner surface of the condenser. Then came 

 the inch-thick circle of steam, on its exit from the 

 cylinder, to be condensed ; and finally an outside circle 

 of cold air, performing the same functions as the inner 

 circle in condensing the steam and carrying its heat 

 back again to the fire. 



The object or principle of this engine was to avoid 

 the loss of heat,, and the necessity for either condensing 

 water or feed-water, as described in the letter and draw- 

 ing of August 19th, 1830, but the detail was changed, 

 mainly to facilitate construction. As in practice it 

 might be impossible to fully attain those objects, pre- 

 paration was made to get rid of the salt from such water 

 as might be required as feed- water to make good the 

 loss from leakage or other defects in the working of 

 marine steam-engines. The specification states : " For 

 the purpose of supplying the boiler with distilled water, 

 in case there should be a deficiency in it, a small vessel 

 made of two upright tubes, one within the other, is 

 placed on the cap-piece. The inner tube is of the same 

 diameter as the flue, and forms a continuation of it. 

 The water being heated by the flue is converted into 

 steam, which, passing into the condenser, is there reduced 

 to water again, leaving the sediment or salt in the sup- 

 plying vessel." 



