ON CONSUMPTIOX OF FUEL AND PREVENTION OF SMOKE. 119 



which take place in the combination of the hydrogen with oxygen, the bulk 

 of the products is found to be to the bulk of the atmospheric air required 

 to furnish the oxygen, as 10 is to 11. The amount is therefore 49- 104. This 

 is without taking into account the augmentation of the bulk due to the 

 increase of the temperature. In the combination which takes place be- 

 tween the carbon and the oxygen, the resultant gases (carbonic acid gas and 

 nitrogen gas) are of exactly the same bulk as the amount of air, that is, 

 105"71 cubic feet, exclusive, as before, of the augmentation of bulk from the 

 increase of temperature. The total amount of the products of combustion 

 in a cool state would therefore be 49"104.< + 105"71 = 154'"8I4 cubic feet. 



" The general temperature of a furnace has not been very satisfiictorily as- 

 certained, but it may be stated at about 1000^ Fahrenheit, and at this tem- 

 perature the products of combustion would be increased, according to the 

 laws of the expansion of aeriform bodies, to about three times their original 

 bulk. The bulk, therefore, of the products of combustion which must pass 

 off must be 151"S14 x 3 = ^S-i-^i-^ cubic feet. At a velocity of 36 feet per 

 second*, the area, to allow this quantity to pass off in an hour, is '516 square 

 inch. In a furnace in which 13 lbs. of coal are burnt on a square foot of 

 grate per hour, the area to every foot of grate would be "516 x 13 =6"708 

 square inches ; and the proportion to each foot of grate, if tlie rate of com- 

 bustion be higher or lower than 13 lbs., may be found in the same way. 



" This area having been obtained, on the supposition that no more air is 

 admitted than the quantity chemically required, and that the combustion is 

 complete and perfect in the furnace, it is evident that this area must be much 

 increased in practice where we know these conditions are not fulfilled, but 

 that a large surplus quantity of air is always admitted. A limit is thus found 

 for the area over the bridge, or the area of the flue immediately behind the 

 furnace, below which it must not be decreased, or the due quantity could 

 not pass off, and consequently the due quantity of air could not enter, and 

 the combustion would be proportionally imperfect. It will be found ad- 

 vantageous in practice to make the area 2 square inches instead of '5 16 square 

 inch. The imperfection of the combustion in any furnace, when it is less 

 than 1'5 square inch, will be rendered very apparent by the quantity of 

 carbon which will rise unconsumed along with the hydrogen gas, and show 

 itself in a dense black smoke on issuing from the chimney. This would give 

 26 square inches of area over the bridge to every square foot of grate, in a 

 furnace in which the rate of combustion is 1 ^ lbs. of coal on each square foot 

 per hour, and so in proportion for any rate. Taking this area as the pro- 

 portion for the products of combustion immediately on their leaving the 

 furnace, it may be gradually reduced, as it approaches the chimney, on ac- 

 count of the reduction in the temperature, and consequently in the bulk of 

 the gases. Care must however be taken that the flues are nowhere so con- 

 tracted, nor so constructed, as to cause, by awkward bends, or in any other 

 way, any obstruction to the draught, otherwise similar bad consequences will 

 ensue." 



From this statement it would appear, that 26 square inches of area over 

 the bridge is about the correct proportion for the combustion of 13 lbs. of 

 coal per hour on each square foot of grate-bar. Now these proportions are 

 rather more than is given in stationary boilers; as the mean of a number of 

 experiments, taken where the combustion was most perfect, gave about 18 

 square inches over the bridge, and about 28 square inches as the area of the 

 flues to every square foot of grate-bar. 



* See Dr. Ure's experiments, reail before the Royal Society, June 1836. 



