336 TUBULAR BOILER, SUPERHEATING STEAM, 



water, f)(J feet above the bottom. This was done with two 

 bushels of coal per hour, therefore it will not cost above one 

 penny per square fathom to lift the sand over this embankment. 

 It is intended to get down Mr. Telford to give his opinion on it. 

 Your remarks on it would be of service. 

 " I remain, Sir, 



" Your humble servant, 



" RICHARD TREVJTHICK." 



The writer having worked at these experiments, 

 knows that their object was to employ high-pressure 

 steam in the boiler, using it very expansively in the 

 cylinder, and by cold surface sides reducing its bulk 

 either to low-pressure steam or boiling water, and then 

 force it again into the boiler. 



" MR. GILBERT, " HAYLE FOUNDRY, November l-ith, 1829. 



'* Sir, I have both of your letters and sketches, which 

 shall be put in hand. I understand it perfectly well. Since I 

 wrote to you last I have made several satisfactory trials of the 

 engine, and think it unnecessary to make any further experiments. 

 The statement below may be depended on for a future data. 

 The load of the engine was 6280 Ibs., being 20 Ibs. to the inch 

 for a 20-inch cylinder with a 6-feet stroke, 12 strokes per minute, 

 with three-quarters of a bushel of coals per hour, giving a duty 

 of 361,728,000 for 1 bushel of coal, a duty far beyond anything 

 done in the county by so small an engine. The cold water 

 sides round the condenser was 60 feet, and the water at 

 112 degrees temperature, not having a sufficient stream of cold 

 water to supply the cistern. Each foot of cold water sides 

 did 7536 Ibs. per minute, about three times the work done in 

 the county per foot of hot boiler sides ; therefore the condenser 

 need not be more than one-third of the boiler sides. By making 

 the condenser of 4-inch copper tubes and of an inch thick, it 

 would stand in one-twentieth part of the space of the boiler. 



" I put a boiler naked to try cold air sides ; it was very rusty, 

 and did not condense as fast as I expected. The engine worked 

 exceedingly well, but slow. The duty performed for each foot of 



