350 TUBULAR BOILEE, SUPERHEATING STEAM, 



that the extreme safety of my improved steam-engine will be 

 seen, from considering that in case the boiler should explode 

 inwards into the flue, the power of the steam would be first 

 reduced by filling the flue and fire-place, and could not escape 

 through the chimney and fire doorway faster than it would 

 diffuse itself and be condensed by mixing with the surrounding 

 air, and thus lose all its force. But should the outside of the 

 boiler burst, part of the force of the steam would be spent in 

 filling up the interstices between the particles of the charcoal, 

 and would then probably be too weak to effect a breach through 

 the inner tube of the air-vessel ; and should such a second 

 breach be effected, the space within the air-vessel would allow 

 the steam to expand and partly condense, and a portion to 

 escape into and through the fire doorway, where it would divide 

 itself, and proceed harmlessly up the flue, and out at the door- 

 way ; so that the outer case being a reserve of strength, would 

 to a certainty withstand the force remaining in the steam after 

 the before-mentioned successive reductions of power." 



The patent of February, 1831, perfects the sketch in 

 his letter of July 27th, 1829, which in its turn made 

 more perfect the plans put into practice in 1815, just 

 before leaving England for America. 1 The prejudice 

 against the use of his high-pressure steam-engine he tried 

 to meet by calling it "a high-pressure safety engine." 

 The boiler was of six wronght-iron upright tubes, one 

 within the other. The inner one was the fire-tube, sur- 

 rounded by a tube of larger diameter, forming the water 

 and steam space. This was again surrounded by another 

 tube, 2 inches larger in diameter, the space being filled 

 with charcoal or other non-conductor of heat ; another 

 tube, 2 inches more in diameter, formed the inner circle 

 of the condenser, having an inch space for the passage of 

 cold air from the blowing cylinder, carrying the heat 

 from the condensing steam back to the fire-place. Still 



1 See Trevi thick's letters, July 8th, 1815, vol. ii., p. 80, and 7th, vol. i., 

 p. 364 ; and 16th May, vol. i., p. 370 ; and patent of Iblo, vol. i., p. 375. 



