imth Observations on different Fuels. 197 



Lastly, it must be borne in mind that the furnace is to be 

 filled full of fuel ; and that the fuller it is kept, the more 

 steadily and efficiently will it work. If allowed to get low, it 

 burns too fiercely, and heat escapes up the chimney. On the 

 other hand, the throat of the furnace must not be choked up, 

 or the draught may be completely checked ; a few days' experi- 

 ence is the best guide on this point. 



One word of caution may be also necessary on the subject of 

 clinkering and stoking. I am afraid some gardeners will be 

 quite dismayed when they are informed that the last operation 

 is altogether inadmissible. The fuel being thrown in at the 

 top, falls by its own weiglit, and must never be either poked or 

 stirred. When the bars are clogged, they are to be cleared 

 from below with a hook, similar to those employed in Dr. 

 Arnott's stoves, which is furnished with the boilers. If clinkers 

 have formed, which will be easily detected, the aperture above 

 the bars may be opened, and the clinkers dragged out, with as 

 little general disturbance of the fuefas possible. Where Welsh 

 coal is employed, no clinkers are produced, which is a great 

 recommendation of this fuel. But, under all circumstances, the 

 aperture above the bars should be closed, as directed in my 

 former paper, and opened only to remove clinkers. I am par^ 

 ticular in repeating this direction, because I know that many 

 persons will disregard it, and will use this opening to stoke the 

 fire ; the consequence of which will be, that their fires will burn 

 rapidly to waste, and the apparatus be rendered less efficient : 

 nothing but absolute necessity has induced me to give them the 

 opportunity of so doing, by adopting this opening in front. 



The following experiments were made with a ] 0-inch cast- 

 iron boiler, of the 'form described in my former paper. It is set 

 precisely in the manner there directed, with this exception, that 

 instead of a chimney partly brick and partly iron, with 

 a feeding-door in front, as there figured, my chimney 

 is a mere cone of sheet iron, with a T-piece at the 

 top, as shown in the annexed sketch. (j%. 38.) It is 

 2 ft. 9 in. high to the top of the T-piece, 8 in. diameter 

 at the base, and 3 j in. at the top. It is lifted on and 

 off by hand; and, as it is never too hot to touch, if the 

 fire be properly managed, it affords both a criterion of 

 the management of the fire, and a proof that little heat 

 is wasted by the chimney. It is light and easily moved, 

 and its conical form prevents it from being easily 

 blown off, of which there might otherwise be some 

 danger. This boiler is attached to 44? square feet of radiating 

 surface, in a small hot-house, 14 ft. by 12 ft. The heating pipes 

 consist of 22 ft. of 4-inch, and 39 ft. of 2-inch, with a few feet 

 of leaden connecting pipes, and a copper reservoir containing 



