57. To obtain some notion of the economy which has actually been obtained, we may take the alleged performances of the best Cornish engines, and some other interesting practical cases, as examples.[1]
(1) The engine of the Fowey Consols mine was reported, in 1845, to have given 125,089,000 foot-pounds of effect, for the consumption of one bushel or 94 lbs. of coals. Now the average amount evaporated from Cornish boilers, by one pound of coal, is 8½ lbs. of steam; and hence for each pound of steam evaporated 156,556 foot-pounds of work are produced.
The pressure of the saturated steam in the boiler may be taken as 3½ atmospheres;[2] and, conse-
- ↑ I am indebted to the kindness of Professor Gordon of Glasgow for the information regarding the various cases given in the text.
- ↑ In different Cornish engines, the pressure in the boiler
hence the steam-engine worked in this most advantageous way has in reality the very fault that Watt found in Newcomen's engine. This defect is partially remedied by Hornblower's system of using a separate expansion cylinder, an arrangement the advantages of which did not escape Carnot's notice, although they have not been recognized extensively among practical engineers, until within the last few years.
