186 



HOT-WATEli BOILERS 4.ND I'lFES. 



Difference in weight of two columns of water each one foot high, at vcrious 



temveratures. 



The above table has been calculated by the formula given 

 with table IV., (see xA.ppendix,) for ascertaining the specific grav- 

 ity of water at different temperatures. The assumed tempera 

 ture is from 170° to 190°. 



It will be observed, in the foregoing table, that the amount 

 of motive power increases with the size of the pipe ; for instance, 

 the power is four times as great in one of 4 inches diameter as 

 in one of 2 inches, and nearly six times as great in one of 5 

 inches. The power, however, bears exactly the same relative 

 proportion to the resistance, or weight of water to be put in 

 motion, in all the sizes alike ; for, although the motive powder is 

 four times as great in pipes of 4 inches as in those of 2 inches, 

 the former contains four times as much water as the latter. 

 The power and the resistance are, therefore, relatively the same. 



These calculations are given with the view of showing how 

 trifling a cause may impede the proper circulation of the hot 

 water in pipes, and that, when once obstructed, how impossible 

 it is for an apparatus to work. Trifling as this power may 

 appear, yet upon its action depends entirely the efficiency of an 

 apparatus. Seeing that the motive power is so small, it is not 

 surprising that, by an injudicious arrangement of its parts, the 

 motion may frequently be impeded and even destroyed ; for the 

 slower the circulation of the water, the more likely is it to be 

 interrupted in its course. 



