Hood on Xmrmbig Buildings hy Hot Water. 53 



intensity, tliat tlie heat of a building wliich is warmed in this manner will be 

 materially affected by the least alteration in the force of the fire, instead of 

 maintaining that permanence of temperature which is so peculiarly the charac- 

 teristic of the hot-water apparatus with large pipes. 



" 185. These inconveniences and objections against the apparatus, however, 

 are of but secondary importance in comparison with the question which exists 

 respecting its security. But, as there are no means of regulating the tempera- 

 ture in hermetically sealed pipes, so there can be none for limiting the pressure 

 which they sustain ; and it is only by methods far too refined for general use, 

 that the real amount of the expansive force can be ascertained. An apparatus 

 which, to all appearance, therefore, is perfectly safe at any given time of in- 

 spection, may, in a i&N minutes afterwards, have the pressure so much in- 

 creased by adventitious circumstances, as to render it extremely dangerous, 

 particularly if its management be confided to unskilful hands; and each day 

 that it is used must add to its insecurity, in consequence of the pipes which 

 form the coil continually becoming thinner by the action of the fire. 



" 186. This invention undoubtedly exhibits gi'eat ingenuity; and, could it 

 be rendered safe, and its temperature be kept within a moderate limit, it 

 would be an acquisition in many cases, in consequence of its facile mode of 

 adaptation. Its safety would, perhaps, be best accomplished by placing a 

 valve in the expansion-pipe, which, from its large size, would be less likely to 

 fail of performance than one which was inserted in the smaller pipe. If this 

 valve were so contrived as to press with a weight of 135 lb. per square inch, 

 the temperature of the pipes would not exceed 350° in any part : the pressure 

 would then be nine atmosjiheres, which is a limit more than sufficient for any 

 working apparatus, where safety is a matter of importance. 



Chap. X. Summary of the Subject, and General Remarks. 

 Chap. XI. Ventilation. Chap. xii. Hot- Air Stoves. 



There are few gardeners who have not occasion either to 

 erect a hot-water apparatus, or to manage one ; and all such will 

 find Mr. Hood's Treatise of real use. The more it is studied, 

 the more will appear the merits of Mr. Kewley's system. As a 

 slight improvement on the details of this system, it is suggested 

 by Mr. Hood that the return end of the siphon, instead of being 

 continued down through the hot water in the boiler nearly to its 

 bottom, should be continued down the outside of the boiler, and 

 entered horizontally at its bottom. The object is to increase the 

 difference of weight between the returning column in the siphon 

 and the ascending column (which is the grand cause of the much 

 greater rapidity of the motion of the water in Kewley's apparatus 

 than in any other), by preventing the former from receiving any 

 degree of heat before it reaches the bottom of the boiler. It 

 occurs to us that, perhaps, this might be effected by a water-tight 

 case round that part of the returning leg of the siphon which is 

 immersed in the boiler. If this case were of such dimensions as 

 to preserve an inch of dry air all round the siphon, and was 

 open to the atmosphere at the top, an inch or two above the 

 water, very little heat would be conducted from the hot water in 

 the boiler to the cold water in the siphon. Whether the circu- 

 lation, by this means, would be much accelerated, will often de- 

 pend on the temperature of the water in the boiler. \^ a stove 

 were to be kept np to the temperature of 70° or 80°, the water 



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