104 



REPORT — 1844. 



fires, and the principle of form which approaches the nearest to a maximum 

 calorific effect. 



It is obvious that the hemispherical and waggon-shaped boilers are the 

 best calculated to ensure abundance ofspace ; and the furnace being detached 

 and entirely clear of the boilers, a discretionary power is thus vested in every 

 person choosing to experiment as to the length, breadth, or height of the 

 hearth plate and bars which contain the fuel. Hence arise the anomalies 

 which exist, and the innumerable theories which are advocated in every 

 direction for improved furnaces and perfect combustion. 



These discrepancies create great perplexities; and as much depends upon 

 the management of the fire, and the will as well as skill of the engineer, 

 it is next to impossible from such a mass of conflicting evidence to deduce 

 anything like a correct proportional of the area of the grate-bar, and the re- 

 cipient surface. 



From a careful examination of some of the best-constructed boilers and 

 furnaces in Manchester, the following results were obtained : — 



The ratio of grate-bar to absorbing surface is therefore as I : ITl, which 

 taken from fifteen different boilers of the best construction, and worked with 

 considerable skill, gives a fair average of the proportions of the furnace and 

 flue surface of each. Now, on comparing the above with the boilers at work 

 in Cornwall, it will be found that their relative proportions are as 1 to 2.5 ; 

 the Cornish boilers presenting from two and a half, and in some instances 

 three times the surface exposed to the action of the fire, in the ratio of the 

 furnace to the flue as a recipient of heat. Taking the disparities as thus 

 exhibited, it must appear evident that exceedingly defective proportions 

 must somewhere exist, otherwise the anomalous comparison of a small fire 

 and a large absorbent surface could not be maintained, unless the former 

 practice of large fires and limited flue surface had been found injurious and 

 expensive. That a great waste of valuable fuel is the con.sequence of these 

 defective proportions is abundantly manifest from the results obtained in the 

 quantity of water evaporated by a pound of coals in each. For example, 

 1 lb. of good coal will evaporate in the Cornish boiler about 11 1 lbs. of water, 

 and the utmost that the best waggon-shaped boiler has been known to ac- 

 complish is 8-7 lbs. of water to the pound of coal. Hence the advantage of 

 a small furnace and large flue surface, united however to abundance of boiler 

 space, in order to attain a maximum effect by a slow and progressive rate of 

 combustion. From the facts thus recorded, and the returns regularly made 

 of the performances of the Cornish engines and boilers, it will no longer ad- 

 mit of doubt as to the superiority of the practice which exists in one country 

 as compared with that in the other. Persons unacquainted with the subject 

 have attributed the saving to the engine; but that doctrine, although in some 

 degree correct, is no longer tenable, as experiments, and the monthly re- 



