AND SURFACE CONDENSER. 357 



The enlarging the fire-place end of boilers or fire- 

 tubes has led to many forms. Trevithick's model of 

 1796 1 had an oval tube giving a greater spread of fire- 

 bars ; the same is seen in the 1808 steamboat; 2 the 

 Dolcoath boilers of 181 1 3 show the oval arid also 

 the bottle-neck fire-tube ; the Welsh locomotive of 

 1804 4 had the fire-tube contracted at its bend or return 

 portion; the Tredegar puddling-mill fire-tube of 1801 5 

 tapered gradually from the fire-bridge to the chimney 

 end; in the London locomotive of 1808 6 the fire-tube 

 took the bottle-neck shape close to the fire-bridge. The 

 accompanying sketch shows the bottle-neck contraction, 

 only on the top and sides of the fire-tube was to give 

 breadth to the fire-bars d, and thickness to the fire at 

 bridge c, after which the flue portion of the fire-tube 

 was contracted : this boiler was for many years a 

 favourite in Cornwall. The bottle-neck contraction of 



BOTTLE-NECK BOILER. 



the ' Echo ' boiler was similar to the above, except that 

 the enlargement of the fire-place was downwards 

 instead of upwards, and the fire-tube, instead of going 

 through the end of the boiler, returned to near the 

 enlarged fire-place, when it passed out through the side 

 of the boiler to the chimney, just as in the Tredegar 

 puddling-mill boiler ; all those variations were with the 

 object of increasing the fire-grate, and at the same time 

 keeping down the gross size and weight of boiler and 

 its water. 



1 See vol. i., p. 104. 2 See vol. i., p. 335. 3 See vol. ii., p. 169. 



4 See vol. i., p. 181. 6 See vol. i., p. 223. 6 See vol. i., p. 207. 



VOL. II. 2 1} 



