88 MECHANICS. 



Explosive Engine. 



This is an engine set in motion by the explosion of 

 oil gas and atmospheric air, the mechanical force of 

 the explosion being employed to drive the machinery. 

 Percussion powder and other substances that explode 

 by contact may eventually be employed for the same 

 purpose. 



Brown's Pneumatic Engine. 



The principle of this engine is a very sudden ex- 

 pansion and condensation, not of the gases used in 

 the operation, but of the small quantity of water, 

 formed bv the combustion of the hydrogen with the 

 oxygen of the atmospheric air, admitted into the 

 cylinder at every stroke of the engine. It is conse- 

 quently still a species of steam engine with this dif- 

 ference, that the elastic and condensable fluid is gene- 

 rated at a higher temperature from materials admitted 

 into the cylinder itself. The extent of the vacuum 

 produced must depend on the temperature at which 

 the combustion takes place. 



Bulk and Elastic Force of Steam. 



Under mean pressure, at the temperature of 212 

 (the boiling point), the bulk of steam is 1800 times 

 that of water ; or as a ready rule for calculation, a 

 cubic inch of water produces about a cubic foot of 

 steam. Latent heat of steam about 960. 

 At 212 the elastic force of steam isl 



equivalent to the pressure of a > 30 inch. high, 

 column of mercury - J 



At 226 ditto ditto 40 ditto. 



238 ditto ditto - 50 ditto. 



257 ditto ditto 60 ditto. 



273 ditto ditto - 9J ditto. 



285 ditto ditto 95 ditto. 



A cubic foot of steam at these temperatures will be 



