178 HEATING AS APPLIED IN HORTICULTURE. 



other cases where only a small reserve of Greenhouse and Stove/' presents a great 



heat is required for the night. surface to the action of the fire, and, from 



Figs 219 to 224 present other forms, 

 all of which, except the third and fourth, Fig. 226. 



Fig. 219. 



Fig. 220. 



Fig. 221. 



Fig. 222. 



Fig. 223. 



Fig. 224. 



contain but a small quantity of water in 

 proportion to their heating surfaces. We 

 have elsewhere explained that it is not 

 necessary to have a boiler of great capa- 

 city, as the return-pipe is continually 

 bringing in a fresh supply of cold water 

 in proportion to the rate of discharge of 

 hot water by the upper or flow pipe. Fig. 

 219 appears to be the form best adapted 

 for leaden boilers, the expansion and con- 

 traction being more equal than in boilers 

 of other forms; they are thence less 

 liable to lose their shape, or to cause un- 

 equal thickness in the metal. 



Atkinson's original boiler, fig. 225, con- 

 tained a greater 

 quantity of water 

 than was abso- 

 lutely necessary. 

 It had, however, 

 this advantage, 

 that when once 

 heated it conti- 

 heat longer than 



nued to give out its 

 those of less capacity. 



Thomsons boiler — fig. 226 — 

 known by us some years ago in 



made 

 " The 



the mode of settiug, allows full scope for 

 the flame to play round it. 



Burbidge and Healfs new boiler — fig. 

 227. This boiler has been extensively 



employed in 

 the estab- 

 -tT~| lishment 



Fig. 227. 



of 



the royal gar- 

 dens at Kew, 

 |fffl|M and else- 



«| I f J i \ where, and 



1 Iff If' i 8 spoken 



I IIBBHI highly of "as 



M1JH being supe- 



rior" to some 

 of those used in the same gardens. " The 

 fire plays," says our informant, "beauti- 

 fully all round it but he adds, " I think 

 that there is a great deal in setting them 

 properly. It is 2 feet 6 inches in diameter 

 at the top, 1 foot at the contraction, and 

 2 feet at the bottom, and 3 feet deep. It is 

 calculated to heat about 200 feet of 5-inch 

 pipe, and 360 feet of 3-inch pipe. Here 

 at last we have an instance of what may 

 be done by a small boiler, and we are quite 

 sanguine as to the result. The form, how- 

 ever, of this boiler is bad, as that of all 

 circular boilers is ; a long shallow form 

 would have produced the same effect with 

 a much less quantity of fuel." 



These eminent engineers have also 

 another form of boiler in use in the same 

 establishment, upon the sides, bottom, 

 and interior surfaces of which the heat of 

 the fuel is made to play. 



Dalkeith wrougM-iron boiler. — Fig. 228 

 is a section of a boiler of which we have 



