342 cox. 



may hinder combustion, it prevents fine coal from falling through the 

 grate and in this way may partially compensate for its inconvenience. 

 The finer and dirtier coal from Batan Island after correcting for loss 

 of fine coal (i. e., calculated to coal actually burned), and the difference 

 in ash content, gave somewhat lower efficiencies than the larger and care- 

 fully selected sizes. The only apparent difference in the behavior and 

 quality of the various sizes is that the fine coal, high in ash, tends slightly 

 to smother the fire and steam can not be produced at as great a rate as 

 with the larger sizes. An inspection of Table II shows that the first test 

 of the coal from the military reservation with the highest percentage of ash 

 has a less evaporation per unit of combustible actually consumed than the 

 second and third, which contain less ash, and still less than the fourth 

 and fifth which contain still less ash. The variation, however, is not 

 believed to be due to the ash, but is largely accounted for far more easily 



by a consideration of the fuel ratio, i. e., — r-rn ^ — r^n ir~' 



■' volatile combustible matter 



the greater ratio giving the greater efficiency; although that very high 

 ash may reduce the draft, cause a slower rate of combustion and there- 

 fore less complete combustion in the furnace chamber and the range of 

 the water tubes is not without reason. 



Fire iox and grate. — This Bureau has what is ordinarily considered to 

 be a good boiler plant. .However, it has a short fire box and only the 

 usual vertical baffling and this is not sufficient to enable it to be run with- 

 out some black smoke and loss. It is a recognized fact that the loss of 

 heat due to the actual carbon in the escaping gases is small, perhaps never 

 more than 1 per cent, but smoke is a strong indication of the presence 

 of combustible gases the loss of which may amount to several per cent 

 and materially impair the efficiency. 



A short fire box is not at all suited successfully to bum Philippine 

 coal. I have often urged ^' the necessity of a setting with an elongated 

 fire box and combustion chamber for burning this class of coal. The 

 combustion space must be long and large enough for the combustible 

 gases and air to mis thoroughly and to produce comj)lete combustion. 

 The United States Geological Survey has expressed the same opinion 

 and further lays special emphasis on the necessity of an additional 

 baffle wall.^* Such a wall would undoubtedly cause more perfect mixing 

 and therefore more perfect combustion, which is the desired end. It 

 is probable that eddies such as one seeks to attain in a reverberatory 

 furnace, caused by any obstacle in the path of the gases, greatly aid the 

 mixing. Any scheme which works in the direction of retarding the 



"Cox, A. J.: This Journal (1906), 1, 877; Sec. A. (1907), 2, 41. 

 "V. S. a. 8. Bull. (1907), 325, 62. 



