BOILERS AND PIPES. 



231 



pipes is similar. Shallow cisterns are 

 connected with the upper part of the 

 pipes, fig. 311, about 18 feet from each 

 other, by means of hollow screws, shown 

 at a, fig. 312, which admit the water to 

 pass to and fro reciprocally. The capa- 

 city of the cistern is more than sufficient 

 to receive the increased bulk of the water, 

 which expands when heated, and returns 

 again to the pipes as the water cools. The 

 external diameter of the front pipes in 

 this instance is 13 inches, and of the back 

 pipes 10i inches. Each set of pipes is 

 divided in the middle of their lengths, 

 except that the nearest division of the 

 front pipe returns about half way round, 

 the end being in length rather more than 

 60 feet. These water-pipes have inch- 

 and- quarter steam-pipes extending in 

 them their whole length, and returning 

 again, preserving a regular inclination 

 throughout. The back pipes have steam- 

 pipes 1 inch in diameter passing through 

 them in a similar way ; and the feeding- 

 pipes are so arranged that either division 

 of the pipes may be heated separately or 

 in conjunction with the rest. Another ad- 

 vantage of applying this mode of heating 

 is, that as no returning-pipes are neces- 

 sary, as in the common hot-water appara- 

 tus, the bulk of water is doubled, with 

 the same extent of heating surface, and 

 the retaining power of the apparatus is 

 doubled accordingly. The cisterns are 

 farther serviceable for regulating the hu- 

 midity of the house, which can be done 

 with the greatest accuracy by attending 

 to the covers." 



We have stated that, in extensive 

 ranges like that at Sion House, steam 

 may be most advantageously applied ; 

 still, on the other hand, we find far larger 

 spaces heated by hot water, as those of 

 the large conservatories at Chatsworth, 

 and the new palm stoves at Kew. 



In drawing a comparison between the 

 advantages of heating by hot water and 

 heating by steam, it may be observed 

 that, in the former case, it is not desir- 

 able to raise the water to the boiling 

 point, (212°,) because, in such a case, 

 steam would be formed, and, escaping by 

 the top of the boiler or otherwise, would 

 abstract much useful heat from the ap- 

 paratus. In the latter, on the other 

 hand, the water must be maintained at 

 212°, because, at a lower temperature, the 



steam would condense, and also absorb 

 much useful heat. And to effect this 

 temperature, a much greater consump- 

 tion of fuel must take place. From the 

 necessity of maintaining the temperature 

 of 212° in steam-pipes, it is evident that 

 a given length of steam-pipe will afford 

 more heat than the same quantity of hot- 

 water pipe ; but remarks by Hood on the 

 relative permanence of temperature of 

 the two methods quoted at p. 191, will 

 show an advantage in favour of the hot- 

 water system. 



§ 7. — BOILERS AND PIPES. 



Of boilers, there is now a great variety, 

 as the illustrations in this work will show. 

 As it is in form that these principally differ 

 from each other, we may here observe that 

 that form must be the most perfect which 

 presents the greatest extent of surface to 

 the action of the fire, either at bottom, 

 through the centre, or over the sides; 

 but, at the same time, complicated forms 

 should be avoided. The rage for im- 

 provement in this department has led to 

 an endless number of odd shapes, as if it 

 was supposed that the contriver who hit 

 upon the most out-of-the-way form had 

 achieved the greatest feat ; while a large 

 portion of the public, ever on the scent 

 for novelty, have from time to time been 

 severely bitten. The more whimsical 

 and unphilosophical the form, the greater 

 the expense ; the more intricate and com- 

 plicated, the more likely it is to get out 

 of order ; while such forms are not cal- 

 culated to stand the wear and tear which 

 those of more simple construction do. 

 Copper, zinc, wrought and cast iron, and 

 latterly lead and earthenware boilers, 

 have been recommended. Of these, we 

 prefer cast-iron, as being the strongest, and 

 as less liable to corrosion than wrought- 

 iron. The metal requires to be of excel- 

 lent quality, and carefully cast, so as to be 

 of equal thickness throughout, else they 

 are liable to crack upon fire being applied 

 to them for the first time, on account 

 of the inequality of expansion ; and for 

 this purpose they should be gradually 

 heated when first subjected to the fire. 



Copper is expensive, and zinc can only 

 be safely used upon a very small scale, 

 and, like copper and lead, it is incapable 



