28 ANNUAL OF SCIENTIFIC DISCOVER?. 



descent fuel at the back of the furnace is never allowed to burn 

 into holes, has, as we all know, certain advantages. Bat when 

 the back of the furnace is left to itself, I believe it to be a most 

 difficult matter to avoid the admission of cold air en masse, a con- 

 dition which cannot but be attended with loss of efficiency; and 

 in my attempts to discover the best method of mechanical firing, 

 I could not find that those systems in which the coal had a pro- 

 gressive motion from the front to the back were free from these 

 defects. Such methods appear to me to owe their advantages, 

 for no doubt they have advantages, to other causes than that of 

 the perfect combustion of the hydrocarbons ; and is not the com- 

 parative freedom from smoke in this system of firing the result, 

 in a great measure, of that union of carbon from the front with 

 carbonic acid from the back, producing carbonic oxide, and inev- 

 itable loss of heat, the pernicious prjnciple resorted to by a whole 

 army of smoke-burning patentees ? The apparatus which appears 

 to me most correct in principle does not profess to compete with the 

 more perfect mechanical stokers, inasmuch as the clinkers are 

 removed by the firemen in the ordinary manner. In short, since 

 my attention was drawn to the subject, I have come to the con- 

 clusion that the principle of what was probably the first attempt 

 ever made in mechanical firing I speak of Stanley's patent is 

 capable of the highest possible efficiency. Twenty years ago 

 nearly every furnace in Lancashire was fed by the apparatus pop- 

 ularly known as the "hopper." In a box on the front of each 

 furnace 2 fans revolved horizontally. Fuel was drawn from a 

 hopper by rollers which crushed and let it fall on to the 2 fans, 

 which in their turn propelled it into the furnace. It was possible 

 to adjust the speed in such a manner that the fuel was spread 

 uniformly over the whole surface of the bars. I would merely 

 add that when the 2-flued Lancashire boiler replaced the 

 wagon and egg-ended boilers then in use, the hoppers Avere 

 taken down, possibly in some places applied to the new flue 

 boilers, found not to throw the fuel evenly over the bars, and 

 discarded. In Leeds, however, they are still in use to a consid- 

 erable extent, probably because some makers there took the 

 trouble to adjust them to their altered circumstances. For a 

 single 2-flued boiler the hopper, as now in use at Leeds, re- 

 quires about 20 toothed wheels, and at least 2 worms to drive the 

 crushers and other portions ; and notwithstanding the fact that 

 the teeth of those wheels are constantly breaking, and that the 

 whole apparatus trembles under the sudden check caused by a 

 large lump of coal falling between the small crushing rollers, 

 manufacturers who have tried it for so many years give universal 

 testimony as to its economy. I understand that one engineer in 

 Leeds still makes a considerable number of them. This appara- 

 tus does not, of course, prevent smoke, but it distributes the 

 smoke from a given quantity of fuel over a longer period than in 

 hand-firing, and reduces its blackness in the same proportion. 



Now, does it not appear that if we can retain the manner of 

 throwing on the fuel, very considerably simplify the means, and 

 use it in conjunction wiLh the lire-bar arrangement already de- 



