202 SCIENCE OF COMMON THINGS. 



"What is high-pressure steam ? What is a steam-engine ? 



In cookery, if steam raised from boiling water be 

 allowed to pass through meat and vegetables, it will be 

 condensed upon their surfaces, imparting to them the 

 latent heat which it contained before its condensation, 

 thus cooking them as effectually as if they were im- 

 mersed in boiling water. 



1341 What do we mean when we speak of high-pressure steam f 



High-pressure steam is merely steam condensed, not 

 by withdrawal of heat, but by pressure, just as high- 

 pressure air is merely condensed air. To obtain a 

 double, triple, or greater pressure of steam, we must 

 have twice, thrice, or more steam under the same vo- 

 lume. 



1343 Is high-pressure steam, escaping from a boikr heated to 300 or 

 more, hotter than low-pressure steam escaping from a boiler at 212 ? 



No ; for the instant that high-pressure or condensed 

 steam escapes into the air, it immediately expands and 

 becomes low-pressure steam, and is greatly cooled down 

 by its expansion. 



1343 Does high-pressure steam, acting in a boiler at a high tempera- 

 ture, exert a greater mechanical and chemical power than low-pressure 

 steam f 



It does f high-pressure steam acting upon bones, 

 breaks up and dissolves the whole mass, extracting all 

 the glue and fat, when ordinary steam would dissolve 

 nothing. 



In the Western States, where large quantities of lard are manufactured, 

 the whole hog is exposed to high-pressure steam, and the carcass reduced 

 in a short tune to a fat fluid mass. 



1344 Can high-pressure steam be raised to a very elevated degree of 

 heat? 



It can / in some of the methods lately introduced for 

 purifying oils, etc., the temperature of the steam, before 

 its application, is required to be sufficiently elevated to 

 enable it to melt lead. 



1345 What is the steam-engine f 



The steam-engine is a mechanical contrivance by 

 which coal, wood, or other fuel is rendered capable of 

 executing any kind of labor. 



