SECT. ii. J PROPERTIES OF STEAM. 89 



relative bulk and pressure of the steam, the height of the column of steam will be 



found. 



C~ 1 Ib. per square inch is 2'31 feet. 



The height of a column of water at 60 equivalent to I 1 Ib. per circular inch is 2-94 feet. 

 the pressure of j 1 inch of mercury is 1'133 feet. 



[_ the atmosphere is 34-0 feet. 



The water is supposed to be of the temperature 60, and the atmosphere equal to 

 a pressure of 30 inches of mercury : the bulk of the steam will depend on the 

 pressure and temperature, and will be given for the range of practice in a table at 

 the end of the volume, or may be found by art. 121. For example, the volume 

 of steam at 212 being 1711 times the bulk of the equivalent quantity of water at 

 60, and the pressure being 30 inches of mercury, or 34 inches of water, we have 

 1711x34=58174 feet, the height of an atmosphere of steam at 212. 



136. If an aperture were formed so that there would be no oblique action in 

 passing it, a gaseous fluid or vapour would rush through it into a perfect vacuum, 

 with the velocity a heavy body would acquire in falling through the height of the 

 column of the same fluid equivalent to the pressure. 



And this velocity in feet per second is equal to eight times the square root of the 

 height of the column ; l but through pipes and other apertures the velocity will be 

 only 5, or 6^, or other number of times the square root of the height of the column, 

 as shown in the table, art. 133. for each kind of aperture. 



137. RULE. If the height of a column of steam equivalent to the pressure of 

 steam in a boiler be determined, and also the height of a column of the same steam 

 equivalent to the pressure on the piston of a steam cylinder, then the velocity will 

 be equal to 6 '5 times the square root of the difference between the heights of the 

 two columns. This result is the velocity in feet per second through a straight pipe. 



1 In algebraic notation ; let / be the inches of mercury equal to the force of the steam or the 

 pressure on the fluid, b the bulk of the fluid when the same weight of water is 1, and h = the 

 height of an atmosphere of the fluid of uniform density. Then, 1-13 fb^=h ; and 



8 >/* = w = 8 V 1-13/4, 



when the fluid flows into a perfect vacuum without contraction at the aperture. In the best 

 formed pipes it is 



in common formed ones 



6-5 Jh = v. But * = 76-5(459 + (art m) . 



hence 



v = 6-5 v/86-5 (459 + ^), the velocity into a vacuum, 

 when t' is the temperature of the steam. 



X 



