i879-] HEATING BY HOT WATER. 231 



no hesitation in saying that ' ' the circulation of the water in the pipes will be 

 as rapid with the bottom of the boiler one foot below the level of the return 

 pipes as it would be supposing the boiler was sunk several feet deeper." If by 

 this he means that it makes no difference to the circulation whether it is 2 

 feet or 4 feet from the lowest point where the return enters the boiler to the 

 highest point (whether this highest point is at the far end or immediately above 

 the boiler) of the flow-pipe, then I say, that I have no hesitation in stating that 

 Mr Hammond is labouring under a grievous mistake. Those having practical 

 experience know that, where it is practicable to place the boiler — say 10 or 

 12 feet below the floor upon which the pipes are laid — there is a very much 

 more rapid circulation than where there is only say 3 feet of difference between 

 the bottom of return and top of flow pipes. This result is what any one acquainted 

 with the motive power at work in a hot-water heating apparatus would expect. 

 Mr Hammond enters into this question ; but evidently it is a subject which he 

 has not yet mastered. It seems to me that the "primary reason " he gives " why 

 water circulates or moves in pipes " is just, to put it in plain language, because 

 water is water, a fluid, and not a solid, like iron, stone, lead, or ice. He seems 

 also to be of opinion that one particle of water cannot transmit its heat to an 

 adjoining particle, or, in other words, that water is an absolute "non-conductor." 

 This is an error. Water, as well as all fluids and gases, is not a good conductor ; 

 but it would be a serious mistake for any one to run off with the idea that it has 

 no power to transmit any heat by conduction. It is unnecessary to follow Mr 

 Hammond through his explanations of the principles upon which the water circu- 

 lates, but to show the utter fallacy of the idea that water circulates as rapidly in an 

 apparatus of (say) 4 feet mean height between its lowest and its highest points, 

 as in one with 10 feet, I will quote the formula of one of the greatest living 

 theoretical engineers, Mr Kinnear Clark, of London, who, in his splendid work, 

 ' A Manual of Rules, Tables, and Data for Mechanical Engineers,' page 485. says, 

 when treating of the circulation of hot water, " The velocity of circulation is 

 that of a falling body, due to the difference of height of two columns of water of 

 equal weights of pressure on the base, and it varies on the square foot of the dif- 

 ference of height. The velocity may be found by the aid of Table, No. 85, page 

 280. The difference of height is proportional to the difference of volumes, Table 

 No. 109 ; and if the mean height is increased in the same proportion, the in- 

 crease will be the height from which the velocity is to be calculated. For ex- 

 ample : let the mean height be 10 feet, and the difference of average tempera- 

 tures of the two columns 10° F., say between 170° and 180°. The respective 



volumes are as 1.0269 and 1.031, and 10 feet x ~^q 9 = 10 - 04 feet - Then 



10.04 — 10 = 04 feet the difference of height; and the velocity due to this 

 height is 1.61 feet per second, or 96.6 feet per minute. If the height be 20 feet, 

 the difference is .08 feet, for which the velocity due is 136.20 feet per minute. 

 In practice, of course, the velocities due are not attained, nor, at least in the 

 more complex forms, nearly attained. The actual velocities are in some cases 

 not more than a half, or even a ninth, of the velocities due to gravity. " This 

 quotation proves conclusively the great value of having depth of stokehole. 



And, moreover, when Mr Hammond speaks of his proposal not being appli- 

 cable where the pipes have to "cross under outside paths," why does he leave 

 out of consideration inside paths ? Is it not a fact that inside paths make the 

 application of the method proposed impracticable as well as outside paths ? And 

 is it not a fact that there are only very few places where there are neither out- 

 side nor inside paths to contend with in the way of having to cross under them ? 



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