348 



cox. 



oxygen unites readily with carbon monoxide to form carbon dioxide or tlie 

 hydrogen with oxygen to form water or hydrogen peroxide. If the dissociation 

 equilibrium is disturbed in either of these ways, more water molecules dis- 

 sociate into hydrogen and oxygen atoms. Wlien a tem[jerature of the furnace 

 is reached where this dissociation takes place faster than the dissociation of the 

 oxygen molecules of the air, we have an explanation of the catalytic action of 

 water in the combustion of coal and why a high combustion chamber tem- 

 perature is desirable. 



In the combustion of a highly bituminuous coal, the extent of the loss 

 due to the carbon monoxide and hydrocarbon gases of the gasified coal, 

 passing u-p the stack before combustion is complete may be seen by an 

 examination of the foUowinsr table: 



Element. 



Product of combustion. 



Heat of 

 combustion 

 in calories.22 



Carbon 



Carbon mono.xide 



Carbon dioxide 



2,435 

 8,140 

 34,180 



Do — _ 



Hj'drogen 



Water 







It will be observed that each unit of carbon burned only to carbon 

 monoxide will result in a loss of 5,715 calories (over half) and each 

 unit of hydrogen unburned will result in a loss of 34,180 calories. In 

 these experiments this loss has been regulated as well as possil)le with 

 the dampers and air supply at my disposition, but a difEerence in 

 construction of the boiler plant would seem advisable for some of the 

 varieties of coal. Approximatel}' jDerfect combustion can be obtained 

 by proper boiler and furnace design, construction and operation. 



An extremely rapid rate of evaporation, a low chimney temperature 

 and completeness of combustion are incompatible. Messrs. Brecken- 

 ridge, Parr and Dirks -^ found that the maximum rate of evaporation 

 was obtained with the boiler running at its rated capacity, with the 

 flue-gas temperature at about 260° C. With an increase in the rate of 

 combustion the flue-gas temperatuxe increased and the evaporation 

 dropped off. Most of the Philippine coals easily gave a rate of evapora- 

 tion equal to that obtained vnth Australian coal on an ordinary run. 



Absorption. — Highly bituminous coals are likely to cause a deposit 

 of soot which reduces the efficiency of the lieating surface. Boilers 

 must be thoroughly cleaned .before beginning tests. The necessity for 

 this precaution is evident in that if the drum and tulaes are insulated 

 from the hot gases on the one side by a layer of soot and from the water 

 on the other by a layer of scale, the absorption will be imperfect and the 

 greater this insulation the more resistance to absorption and tlie greater 



^ Calculated from the numbers of J. Thomsen : Thermo-chemische Untersuch- 

 ungen (1882), 2, 52, 283 and 288. 

 ■'Univ. of in. Bull. (1906), 3, 39. 



