AM) SURFACE CONDENSER. 329 



heating steam and surface condensation culminated in 

 the Binner Downs experiments of 1828, one immediate 

 practical result of which was the tubular surface con- 

 denser, enabling steamboat boilers to avoid, in a great 

 measure, the use of salt water, facilitating in a marked 

 degree the application of marine boilers and engines 

 with steam of an increased pressure. 



The Binner Downs engine, with a cylinder of 70 

 inches in diameter, and a stroke of 10 feet when working 

 with steam in the boilers of 45 Ibs. to the square inch 

 above the atmosphere, and using the heating flues around 

 the cylinder, required 13 gallons of injection- water at 

 each stroke, and consumed at the rate of 3 bushels of 

 coal an hour, to produce a duty equal to eighteen 

 millions; by removing the cylinder superheating flues, 

 the quantity of injection-water for the same amount of 

 work increased to 15i gallons, and the coal to 4i bushels. 

 Watt's rule for his low-pressure steam vacuum engine 

 doing a duty of eighteen millions, gave 57 gallons of 

 injection- water, and Hi bushels of coal. 



On the question of coal, this statement agrees very 

 nearly with Trevithick's letters of sixteen years before, 

 when he used the high-pressure boilers in the Dolcoath 

 pumping engine, 1 promising .that his high-pressure ex- 

 pansive engine would do the work with one-third of the 

 coal required in the low-pressure vacuum engine. 



The high-pressure steam required a less amount of 

 injection-water to condense it than the low-pressure 

 steam, in proportion to the work done, showing the 

 Watt rule and the Watt experience to be inapplicable 

 to high-pressure engines ; for instead of 57 gallons of 

 injection- water the Binner Downs engine with steam of 

 45 Ibs. to the inch required but 15i gallons of injectioii- 



1 Si-c vol. ii., p. 171. 



