PHILIPPINE COALS AS FUEL. 351 



economy in the working of blast furnaces by reducing the moisture in 

 the air blast to a low and practically constant amount. It is stated 

 as demonstrating this economy that prior to drying the air, throughout 

 a period of eleven days the daily production of iron in the blast furnace 

 was 358 tons with an average consumption of 2,147 pounds of coke per 

 ton of iron, while for a period of sixteen days when the dry-air blast 

 was used the daily production of iron was 447 tons with an average 

 consumption of 1,726 pounds of coke per ton of iron. This shows a 

 credit balance of 20 per cent greater output of iron and 20 per cent 

 reduction in fuel consumed per unit of pig ii'on and output. However, 

 there are other considerations. Unquestionably the greater out23ut was 

 largely caused by the more perfect maintenance of the regularity of the 

 furnace owing to the practically constant amount of water in the blast. 

 The gases in the former case were composed of 22.3 per cent of carbon 

 monoxide and 13 per cent of carbon dioxide escaping at a temperature 

 of 538° and in the latter of 19.9 per cent of carbon monoxide and 16 

 per cent of carbon dioxide escaping at a temperature of 376°, so that 

 the economy of fuel is partly traceable to more perfect combustion and 

 less loss through the escape of the gases. However, the fact remains 

 that the saving through the use of dry air and the loss due to the specific 

 heat of the moisture in the use of ordinary air is a great one, and this 

 applies alike to all combustion furnaces. 



The moisture of the air is a large factor in the tropics, where the 

 atmosphere is of almost unvarying temperature, the thermometer normally 

 standing at 30°, and the humidity is high, the air often being almost 

 completely saturated. The average weight of the water entering the 

 furnace in the above tests was about 5 per cent of the water evaporated 

 in the boiler. 



Even when all of these factors are taken into consideration there are 

 sometimes abnormalities in the evaporative efficiency of a boiler which 

 it is hard to explain. Some boilers owing to individual superiority, 

 due to rapidity of water circulation, the use of water that does not foam, 

 etc., are more efficient than others ; some furnaces bum all of the volatile 

 matter of a coal while others waste it and even the same furnace behaves 

 differently with different coals. 



Theoretically, the volatile matter should be expelled from a coal on the 

 grate and the fixed carbon simultaneously burned, thereliy keeping the 

 fuel bed intensely hot. The combustion of the volatile combustible 

 matter should be coinpleted in the combustion chamber. Coals high in 

 fixed carbon burn with a short, hot, smokeless flame and combustion is 

 nearly completed a short distance above the fuel l^ed, but with higlrly 

 volatile coals the combustion is incomplete even at the rear of the 

 combustion chamber. 



