38 INTRODUCTION TO GENERAL SCIENCE 



26. THE STEAM ENGINE 



Another application of the laws of nature is instanced in 

 the case of the steam engine. When a liquid evaporates, the 

 average velocity of its molecules is much greater than that 

 which they had in liquid form. When these rapidly moving 

 molecules strike the walls of any container which restrains 

 them from unlimited motion, they exert a pressure upon the 

 walls that is proportional to their velocity. The latter in- 

 creases with the temperature. When water is boiled, evap- 

 oration takes place rapidly, and the steam may also be 

 heated far above the boiling point. Therefore we can obtain 

 any pressure we may desire. 



The steam so generated is conducted alternately, by means 

 of automatic valves, to the opposite sides of a moving piston 

 which slides in a cylinder. The references give complete 

 details concerning various kinds of steam engines. 



References : - 



1. 1803:186-191. The Steam Engine. 



a. 1801 : 297-299. The Steam Engine. 



6. 1804: 308-313. The Steam Engine and the Locomotive. 



c. 1805 : 312-314. The Steam Engine. 



d. 1806:381-386. The Steam Engine. 



e. 1807:212-213. The Steam Engine. 

 /. 1808 : 245-247. The Steam Engine. 

 g. 1809:203-207. The Steam -Engine. 

 h. 1810 : 190-193. The Steam Engine. 



27. DISTILLATION OF LIQUIDS 



There is very little water which does not contain some 

 solid dissolved in it. It may be purified, however, both by 

 natural and by artificial methods. The evaporation from the 



