1879.] HEATING BY HOT WATER. 57 



point of the boiler, throughout the structures to be heated, it is impos- 

 sible for the hottest volume of water contained in the apparatus to 

 occupy the highest point of the latter, when heat is applied to the 

 boiler. The reason for this is plain : as soon as the fire acts on the 

 boiler, the particles of water in contact with its inner surface bound 

 upwards, continuing to do so until they come in .contact with the inner 

 surface of the upper side of the flow-pipes. Here the particles imme- 

 diately part with a portion of their heat, and consequently become 

 of greater specific gravity than they were at the time of starting on 

 their upward course, and would now commence to descend towards 

 the point from which they started, but that they are still lighter than 

 the particles composing the body of cold water contained in the flows 

 at the time of setting the fire agoing : hence the partially cooled par- 

 ticles proceed along between the colder body of water and the inner 

 surface of the upper side of the flows, continuing to do so until the 

 cold water has found its way to the boilers in a contrary direction. 

 Thus, to begin with, we have two bodies of water of different degrees of 

 temperature moving in opposite directions in the same pipe, and at the 

 same time. This fact hot-water engineers admit, but tell us that as 

 soon as all the water in the flow-pipes becomes of equal temperature 

 the process will cease ; and no doubt it would, providing it were possible 

 for all the water in the flows to become of an equal temperature. This, 

 however, cannot occur in an apparatus of any great extent so long as 

 combustion takes place below the boiler; and for this reason the water, 

 as it travels from the hottest towards the coldest point of the appar- 

 atus, is continually parting with its heat, and the coldest particles in 

 the volume of water at any given point of the apparatus will occupy 

 the lowest place ; consequently the coldest particles, throughout the 

 length of the pipes, will rest on the inner surface of their under side, 

 and as the inner surface of the under side of the flows descend in the 

 direction of the top of the boiler, the coldest or heaviest particles of 

 the water contained in them will roll or gravitate down the inclined 

 plane, just as the coldest or heaviest particles did at the time of 

 starting the fire under the boiler. On these grounds we say that a 

 continuous rise in the flow-pipes is a hindrance rather than otherwise 

 to the circulation of the water. Therefore, the flow-pipes of a properly 

 adjusted hot-water apparatus should be carried to the highest point of 

 action in the structures to be heated as soon after they leave the boiler 

 as the general arrangements of the structures and the position of the 

 boiler in relation thereto will admit, and from this point the pipes 

 should gradually descend until they connect with the boiler again at 

 its lowest point. Thus the heated water, when it leaves the boiler, 

 cannot return when it becomes colder except by the legitimate route 

 of travelling through the whole length of the pipes, and entering at 

 the lowest point of action of the apparatus. J. Hammond. 



Brayton Hall. 



