102 



HEAT OR CALORIC. 



" It has been found, that when the effort made by the steam to 

 escape, in opposition to the valve thus loaded, is equal to about fif- 

 teen pounds for every square inch, in the area of the aperture, the 



height of the column of mer- 

 cury, C, C, raised by the same 

 pressure, is about equal to that 

 of the column of this metal, 

 usually supported by atmos- 

 pheric pressure, in the tube 

 of a barometer." 



" Hence the boiler, in this 

 predicament, is conceived to 

 sustain an unbalanced press- 

 ure equivalent to one atmos- 

 phere, and for every additional 

 fifteen pounds per square inch, 

 required upon the safety valve 

 to restrain the steam, the 

 pressure of an atmosphere is 

 alleged to be added. To give 

 to steam at 212, or the boil- 

 ing point, such an augmenta- 

 tion of power, a rise of 38 

 is sufficient, making the tem- 

 perature equal to 250. To 

 produce a pressure of four at- 

 mospheres, about 293 would 

 be necessary. Eight atmos- 

 pheres would require nearly 

 343." 



" When, by means of the 

 cock, an escape of steam is 

 allowed, a corresponding de- 

 cline of the temperature and 

 pressure ensues." 



" If the steam, as it issues 

 from the pipe, be received un- 

 der a portion of water of known 

 temperature and weight, the 

 consequent accession of heat 

 will appear surprizingly great, 

 when contrasted with the ac- 

 cession of weight, derived from 

 the same source. It has in 

 fact been ascertained, that one 



