1879.] HEATING BY HOT WATER. 327 



I am quite prepared to believe what "J. H" says in support of Mr Ham- 

 mond's system. Hot water is wonderfully accommodating where it has but 

 one way to circulate. I am acquainted with an old fitter who boasts of his 

 firm having successfully heated a house for a gentleman with only one pipe for 

 both flow and return. (He did not say it was a four-inch.) "J. H." will no 

 doubt be done for ever with the "old system." Suppose, now, for the sake of 

 experiment, he was to fix pipes to his boiler, and give them the usual ascent 

 from, and descent to, the boiler, does he believe that he would get as good a 

 circulation in the pipes that descend from the boiler as in those that/ascend ? 

 I venture to predict that the water would flow into the latter in preference to 

 the former, if no check is put upon it in the shape of a valve. I shall not tres- 

 pass further upon your valuable space. E,. Inglis. 



III. 



I have been rather interested the last few months in the question which has 

 been raised by Mr Hammond on the circulation of hot water, and I think he 

 is entitled to many thanks for bringing forward such a subject for discussion. 

 I understand the main point raised in his first paper to be this : Is a continuous 

 rise in the flow-pipe a hindrance to the circulation ? Hot-water engineers say 

 it is not, but I think a rational view of the case may prove the contrary. 

 While quite agreeing with the correctness of Mr Makenzie's quotation from 

 Mr Clarke's tables, I would only ask, Why continue the rise throughout the 

 whole length of the flow-pipe ? Is it done to give an increased fall to the body 

 of water in the return-pipe, or is it to assist the circulation in the flow ? If 

 the latter, I think the proper designation ought to be the force-pipe. Mr 

 Hammond points out, in his reply to Mr Inglis (p. 210), "The water owes its 

 expansion and relative lightness to heat, in the first instance, and as heat fails, 

 the water contracts and becomes heavier ; it therefore follows that the heated 

 volumes of water should reach the highest points of the apparatus before any 

 diminution of their temperature takes place," — and goes on to say, that when 

 this point is reached by a slow gradient, the water must have become colder 

 than at the time it left the boiler ; and of course the greater distance it travels, 

 the greater is the decrease of temperature — that every inch it has to be raised 

 thereto adds an extra tax on the "pushing and pulling" powers of the colder 

 and heavier water in the return-pipes. With which I entirely agree ; and not 

 only must this be the case, but every inch it has to be raised in the length of 

 the flow is a gradually increasing tax on its own powers of flow. 



Mr Hammond says, at p. 57, "As soon as the fire acts on the boiler, the 

 particles of water in contact with its inner surface bound upwards, until they 

 come in contact with the inner surface of the upper side of the flow-pipes. 

 Here they part with a portion of their heat, and 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 whence they started, but 

 that they are still lighter than the particles composing the body of cold water 

 in the flows," &c. So they would, but I would also take into account the cold 

 water rushing in from the return-pipes, which I think is one of the principal 

 causes of circulation ; and as an instance of the descent of the w r ater after reach- 

 ing the top of the boiler, and the absence of this return current, I need only 

 mention the homely illustration of a common tea-kettle. Therefore I should 

 consider that to have the highest point of circulation as near to the boiler as 



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