134 OF THE GENERATION AND [SECT. in. 



grate next the hopper, and the fuel is pushed back from time to time along the 

 grate, and at the end vitrified portions fall into a cavity, the bottom of which 

 is furnished with horizontal slides. These, when drawn out by an iron hook 

 applied to the handle of the slide, discharge the clinkers into the ash-pit. (See 

 Plate ii.) 



249. The defect of Roberton's method as well as Mr. Watt's consists in 

 admitting a regular current of cold air when it is not regularly wanted, and where 

 it has an injurious effect in cooling the smoke as it rises against the bottom of the 

 boiler. This is greatly remedied by admitting air by means of small side flues, 

 or at the back of the fire, whence having to pass from the ash-pit, through small 

 channels in the hot brickwork, it becomes heated before it issues into the fire-place. 

 But abundance of air will pass the grate if it be properly constructed, and the 

 modification I would recommend is described in Plate 11. 



Air flues, when used, should have valves to open or close them ; and, on the whole, 

 very little good is derived from them unless they be attended to with more care 

 than is usually bestowed on the fire of an engine. 



250. Bruntons Fire-place. In consequence of the difficulty of supplying a 

 fire equably by hand, so as to sustain the regular demand for steam in a steam 

 engine, it has been attempted to use machinery for that purpose. Several schemes 

 have been tried, but the only one which has succeeded in practice is that invented 

 by Mr. William Brunton. 



The method consists in an apparatus for dropping the coals on the grate by 

 small quantities at short intervals of time, (not more than three or four seconds,) 

 and in such a manner that the smoke rising from the fresh fuel must pass over 

 that which is in a further stage of combustion, and consequently be consumed; 

 the uniform supply of air for that purpose being admitted. 



The machine is also so contrived that a quantity of coal is put on proportioned 

 to the quantity of work, and the air admitted is regulated in a similar manner. 



The advantages of such a method are obvious, and the increase of expense of 

 erection not so considerable as might be expected. 



A circular horizontal grate which receives the coals is 5 feet in diameter, and 

 revolves on a vertical axis at the rate of about one revolution per minute. During 

 its revolution the coals fall, from a hopper placed over the boiler, through a 

 vertical narrow rectangular opening, formed through the top of the boiler, of the 

 length and in the direction of the radius of the grate. The quantity discharged 

 at once by the hopper is regulated by the force of the steam in the boiler, and the 

 discharge is made at every fourth or fifth second of time ; by this means an 

 uniform fire, regulated by the work it is to perform, is obtained, and with a 

 certainty as absolute as the nature of things will admit. To prevent air being 



