Sir jfohn Snell 255 



depends entirely on electric power. In Norway four hun- 

 dred thousand horse-power is used in producing nitric 

 acid by this process, and the output is one hundred and 

 eighty thousand tons yearly. 



Electric furnaces are used for the making of special 

 steels. Before the Great War the amount of power used 

 for this purpose in Great Britain was only about three 

 thousand horse-power a year, but by 1918 it had risen to 

 no less than one hundred and thirty-five thousand horse- 

 power, and electric steel was being produced at the rate 

 of two hundred thousand tons a year. From seven 

 hundred to eight hundred units of electricity are used in 

 making a ton of electric steel. 



Here it may be convenient to explain what is meant by 

 a unit of electricity. One B.T.U. (Board of Trade unit of 

 energy) is sufficient to heat about two gallons of water 

 from the temperature of the melting-point of ice to 

 boiling-point. 



Electric power is largely used in making brass, but 

 power must be cheap for this purpose, because every ton 

 melted requires two thousand units. Another important 

 industry is the electrolytic recovery of zinc, a process 

 which absorbs no less than five thousand units per ton. 

 A large factory has recently been erected for this purpose 

 in Tasmania, where water-power is easily obtainable. 

 Chromium, the metal which gives to rustless steel its 

 special qualities, is prepared in electric furnaces, and so 

 too is rustless steel itself. 



Another very important electrical industry is the manu- 

 facture of graphite. Graphite, which is a form of carbon, 

 is much used as a lubricant and for making crucibles. It 

 is best known, however, as the black-lead in pencils. 

 Acheson, the American scientist, noticed that the crater 

 end of a carbon that had been used for arc lighting turned 

 to graphite. Then he discovered that a small amount of 

 silica greatly assisted the change, and worked out a new 



