1JOILKI!, SI' I'KIl 1 1 MATING STEAM, &c. 315 



CHAPTER XXVI. 



TUBULAR BOILER, SUPERHEATING STEAM, AND SURFACE CONDENSER. 



" MB. GILBERT, " HAYLE FOUNDRY, December Uth, 1828. 



" Sir, On my return from London five weeks since I 

 was disappointed at not finding you in Cornwall. I have made 

 iiujuiry into the duty performed by the best engines, and the 

 circumstances they are under, from which it appears to me 

 there is something which as yet has not been accounted for, 

 particularly in Binner Downs engines. A statement was .given 

 to me by Captain Gregor, the chief agent and engineer of the 

 mine, which appears so plain that I cannot doubt the facts, 

 though they differ very widely from all former opinions. There 

 are two engines, one of 42 inches diameter, the other of 

 70 inches diameter, 10-feet stroke. 



" Formerly those engines worked without cylinder cases, when 

 the 70-inch cylinder burnt IJ'wey of coal, and performed a 

 regular duty of forty-one millions ; since that time brickwork 

 has been placed round the cylinder and steam-pipes, leaving a 

 narrow flue, which is heated by separate fires. These flues 

 consume about 5 bushels of coal in twenty-four hours ; the heat 

 is not so great as to injure the packing, which stands good for 

 thirteen weeks ; the saving for several months past has in- 

 creased the duty to sixty-three millions. 



" Before the use of this flue 108 bushels of coal were con- 

 sumed under the boiler, now only 67 bushels are needed, which 

 with the 5 bushels in the flue gives 72 bushels. The coal burnt 

 under the boiler gives a duty of sixty-six millions, or an expan- 

 sion of (JO per cent, by the heat of 5 bushels of coal in the flues, 

 .UK! a duty of 1781 millions gained in twenty-four hours by 

 5 bushels of coal, which amounts to 350 millions gained by 

 each of these 5 bushels. The 42-inch cylinder is as near ;is 

 possible under the same circumstances, no other alterations 



