STEAM AS A WORKING POWER 



3IS 



connected with a machine, work can be obtained from the 

 steam. 



When water is heated in an open vessel, the pressure of its 

 steam is too low to be of practical value, but if on the contrary 

 water is heated in an almost closed vessel, its steam pressure 

 is considerable. If steam at high pressure is directed by noz- 



FJG. 187. Steam as a source 

 of power. 



FIG. 1 88. Steam turbine with many blades 

 and 4 nozzles. (De Laval.) 



zles against the blades of a wheel, rapid rotation of the wheel 

 results just as it did in Figure 184, although in this case steam 

 pressure replaces water pressure. After the steam has spent 

 itself in turning the turbine, it condenses into water and makes 

 its escape through openings in an inclosing case. In Figure 

 188 the protecting case is removed, in order that the form of 

 the turbine and the positions of the nozzles may be visible. 



A single large turbine wheel may have as many as 800,000 

 sails or blades, and steam may pour out upon these from 

 many nozzles. 



