SECT, viii.] MANAGEMENT OF THE STEAM ENGINE. 271 



counter is still used in Cornwall, in order that the effect of the engines may be 

 reported on by the inspectors ; and it is useful in various instances where a check 

 on the consumption of fuel is desirable. 



OF WORKING STEAM ENGINES. 



564. The first attention should be directed to the qualities of the fuel and the 

 water. The fuel, of whatever kind, should be dry, in small parts, and free from 

 earth, &c. No coals should be above the size of an egg, and they should contain 

 as little pyritical matter as possible. Wood should be in billets not more than a 

 foot long, nor two or three inches diameter. The water used should be pure and 

 soft when it can be had. 



All natural waters contain a quantity of matter, which they derive from the 

 strata through which they flow. The purest springs usually rise in beds of gravel, 

 or in siliceous or argillaceous rocks ; and they contain, for the most part, only a 

 minute portion of saline matter, which is principally common salt. The water of 

 limestone or calcareous districts generally contains a much larger quantity of solid 

 matter, most frequently lime in solution, either carbonate or sulphate of lime, which 

 occasions that peculiar quality in waters commonly known by the name of hard- 

 ness. 1 The waters of mines are still more impure ; they often contain earths, acids, 

 alkalies, and saline compounds. Hence water in its natural state is often unfit for 

 a steam engine. 



Almost the only practicable method of improving water is that of exposing it 

 long to the air in ponds : a more effective one is to use the same water over and 

 over again, with only such addition as compensates for loss ; but even this requires 

 a larger reservoir to allow the water time to cool. Foul river-water may be cleared 

 by filtering through sand or gravel. 



To prevent the sediment from the water adhering to boilers, it is common to put 

 in crushed potato, the refuse of malt, and the like, and change it frequently. 



565. For sea-boat engines sea water must be used, and it deposits salt after 

 the water is saturated. This may be prevented by letting a small quantity of hot 

 water escape constantly from the boiler. One hundred parts of sea water contains 

 three parts of its weight of saline matter ; and is saturated when it contains thirty- 



1 Hard waters do not readily dissolve soap, nor form a good lather with it ; on the contrary, 

 they partially decompose it, and a light flocculent substance is produced, which is insoluble in 

 water. 



