ENGINEERING BEFORE AND AFTER WAR 37 



of steam much further than has been found possible in 

 any reciprocating* engine, and owing to this property it 

 has surpassed it in economy of coal, and it realises to the 

 fullest extent Watt's ideal of the expansion of steam from 

 the boiler to the lowest vapor pressure obtainable in 

 the condenser. 



Among the minor improvements which in recent years 

 have conduced to a higher efficiency in turbines are the 

 more accurate curvature of the blades to avoid eddy losses 

 in the steam, the raising of the peripheral velocities of 

 the blades to nearly the velocity of the steam impinging- 

 upon them, and details of construction to reduce leakages 

 to a minimum. In turbines of 20,000 to 30,000 horse- 

 power 82 per cent, of the available energy in the steam 

 is now obtainable as brake horse-power ; and with a boiler 

 efficiency of 85 per cent, the thermo-dynamic efficiency 

 from the fuel to the electrical output of the alternator 

 has reached 23 per cent., and shortly may reach 28 per 

 cent., a result rivalling the efficiency of internal combus- 

 tion engines worked by producer gas. 



During the twenty years immediately preceding the 

 war turbo generators had increased in size from 500 kilo- 

 watts to 25,000 kilowatts, and the consumption of steam 

 had fallen from 17 Ib. per kw. hour to 10.3 Ib. per kw. 

 hour. Turbines have become the recognised means of 

 generating electricity from steam on a large scale, although 

 they have not superseded the Watt engine for pumping- 

 mines or the drawing of coal, except as a means for 

 generating electricity for these purposes. In the same 

 period the engine power in the mercantile marine had 

 risen from 3,900 of the King Edward to 75,000 of the 

 Mauretania. 



As regards the Royal Navy, the engine power of battle- 

 ships, prior to the war, had increased from 12,000 i.h.p. 

 to 30,000 s.h.p., while the speed advanced from 17 knots 

 to 23 knots, and during the war, in ships of the Queen 

 Elizabeth class, the power amounted to 75,000 s.h.p., 



