HEATING. 



219 



boiler, where there is no possibility of solid 

 matter accumulating to cause the iron to burn, 

 and thus destroy the boiler. This boiler is pre- 

 ferable to others when anthracite coal is the 

 fuel used. 



What are called tubular boilers have been 

 much patronized by horticulturists; they are no 



Fig. 284.— Weeks's Duplex Upright Tubular Boiler. 



doubt both powerful and rapid in their action, 

 but they are liable to crack from unequal cast- 

 ing when cast in one piece, and to leak from 

 defective joints when made up of many separate 

 parts. In order to meet these objections Messrs. 

 Weeks & Co., of Chelsea, have provided the 

 Duplex Upright Tubular Boiler, represented by 

 fig. 284, the leading principle of which is that 

 it is made up of two equal parts, which in 

 ordinary cases can be worked as one, and in 

 case of any accidental defect becoming manifest 

 can be at once separated into two, the one half 

 carrying on the work while the other is being 

 repaired. The duplex boiler is made in two 

 sections, each of which consists of the following 

 parts — the upright tubes forming the boiler 

 proper; the horizontal tubes forming the fur- 

 nace; the diaphragm, by which perfect com- 

 bustion of the fuel is obtained; the flow-pipe; 

 the return-pipe. These parts being in dupli- 

 cate, the one half, if need be, can be removed 

 for repairs while the other is left standing in 

 full working order. 



Upright tubular boilers are not suited for 

 common coal, as the products of combustion 

 and the coal-tar and other matters which distil 



from the fuel without being consumed, con- 

 dense upon the tubes if a brisk fire is not kept 

 up; and if these be at too low a temperature to 

 burn them off', the ashes adhere, and so choke 

 the furnace. Coke is preferable, though not 

 indispensable, for the effective working of such 

 boilers. 



Fig. 285 represents another type of boiler, 

 which appears to be constructed on sound prin- 

 ciples. It is called the Centrifugal Boiler, and 

 is invented and constructed by Mr. Deards, of 

 Harlow. It consists of a continuous coil of pipes, 

 constructed of half-circles turned and faced to 

 form a true joint, and held together by clips 

 and screws cast on the pipes. The base of the 

 coil rests on the furnace bars, so that the fire is 

 in the centre, and by an ingenious arrangement 

 of flues, formed by iron plates built into the 

 brickwork, is forced to act upon each separate 

 coil. The upper end is the flow-pipe, along 

 which the heated water travels; and the lower 

 end forms the return-pipe, by which the cooled 

 water is brought back to be reheated. There is 

 provision made for cleaning the flues, and a 



Fig. 285.— Deards' Centrifugal Boiler. 



T-pipe with tap is inserted near the base of the 

 boiler to remove sediment. 



The Rochford Horizontal Tubular Boiler (fig. 

 286) is much in favour with market growers, 

 and is also in use in private gardens, where a 

 powerful and economical boiler is needed. Its 

 essential feature is that the flues are in a direct 

 line to the smoke shaft, ensuring perfect com- 

 bustion and a quick draught, whilst the heat is 

 all absorbed by the extension of the boiler-pipes 



