PHILIPPINE COALS AS FUEL. 345 



Coals which burn low and close to the grate give greatest efficiencies; 

 those which burn high lose much through the grate, give low initial 

 temperature in the fire box, leaving the fuel bed comparatively cool, 

 and the result is combustion at the rear of the chamber, imperfect heat 

 absorption and therefore low efficiency. I think this loss is largely due 

 to the type of boiler, and one should be constructed for these coals that 

 would obviate these losses. I should like to be in a position absolutely 

 to name the best class of furnace for each coal, but not enough tests 

 have been carried on to enable me to do so; however, considerable 

 information as to the best form of furnace has been given. 



Loss through the grate. — A portion of the combustible matter of the 

 coal falls through the grate into the ash pit and is not burned. For a 

 definite coal this varies with the grate and for a certain grate it varies 

 with the coal. It is a most difficult task, not yet accomplished, to con- 

 stnrct a grate that is suitable under any and all conditions of operation. 

 Owing to my inability to have a grate suitable for each coal this 

 discrepancy is much larger in some cases than in others, and therefore 

 I have given, in addition to the usual data, recalculated results to show- 

 the values when this factor is eliminated, i.e., as if this amount of coal 

 had never been fired. 



Draft, chimney gases and loss through the stack. — Draft, measured by 

 the reduction of pressure as compared with that of the atmosphere, 

 which depends on the relation of boiler, furnace, grate and stack, largely 

 controls the air which enters and. the value of the fuel is influenced by 

 it to a marked extent. However, in a boiler plant in the tropics much 

 depends on the direction of the wind, since in most cases the boiler is 

 not protected at the sides. Too much air is better than too little; on 

 the other hand, an excessive amount dilutes the gases, lowers their 

 temjDerature and increases the waste to the stack by an amount equal to 

 the specific heat of the moisture from the excess of air and the heat 

 carried away by the additional quantity of dry chimney gases. The 

 loss up the chimney decreases and the efficiency rises with a reduction in 

 the ■ supply of air until a point is reached at which the loss due to 

 slightly incomplete combustion is just equal to the gain obtained by 

 decreased loss to the stack. Beyond this point the decrease in efficiency 

 is very rapid. It has been my aim to regulate the air supply as much 

 as possible without reducing the completeness of combustion, and in that 

 way I endeavored to control the quantity of gases leaving the system and 

 therefore the waste heat. Without experience with a given coal it is 

 not always possible accurately to supply the proper amount of air for 

 its ideal combustion. It may be noticed from an examination of the 

 tests that a certain amount of carbon monoxide was observed in the 

 chimney gases. This amount was greatest in those from the coal from 



