26 



HOT WATER APPARATUS. 



column (c d) of fluid above the centre of the upper pipe is of a greater 

 weight than the column f e above that centre, motion will commence 

 along the upper pipe fi'om A to B, and the change this motion produces 

 in the equilibrium of the fluid, will cause a corresponding motion in the 

 lower pipe from B to A, and in short pipes the motion will obviously con- 

 tinue till the temperatui'e be nearly the same in both vessels, or if the 

 water be made to boil in A, it may also be boiling hot in B, because the 

 ebulhtion in A ^ill assist the motion." 



Here Mr. Tredgold goes at some length into an investigation of some of 

 the most impoitant points relating to motion that requires attention in prac- 

 tice, wliich want of space compels us to pass over. We cannot, how- 

 ever, refi'ain from making the following quotations : From the common 

 principles of hydi'ostatics and the equations we have obtained,'' says !Mr. 

 Tredgold, the following practical deductions may be derived. 



" 1st. The more expansible tlie hquid is, by a given change of tem- 

 peratiu'e, the greater v^ill be the velocity. 



2ud. All other things being the same, the velocity will be increased in 

 proportion to the square root of the depth of the boiler, therefore, in a 

 boiler four times as deep, the velocity' v^iU be doubled. 



" 3rd. If there be sufficient service of pipe for the object required, a 

 reservoir is not necessaiy to the motion of the water : a simple bent pipe as 

 ^in the annexed chagram, being all that is essential to motion ; the reservoir 

 is only to receive a hot mass of water to maintain the heat after the fire 

 has gone out. 



'''4th. If a boiler has sufficient suiface to receive the effect of the fire, 

 and the whole apparatus contains as much water as will convey the heat 

 from the lire to the heating siutace in the time coiTesponding to its 

 velocity, its capacity need not be fiu'ther increased, except as a reservoir 

 of heat to act when the fire ceases to biu'n. 



5th. Where heat is required only dming the action of the fire, a large 

 surface in proportion to its capacity' may be used with advantage, to give 



