CHARACTERISTICS OF PHILIPPINE COAL. 15 
We tried to operate continuously on this coal alone, but found 
it was not practicable, as results were obtained similar to those 
reported in Table IV, and we could not keep up steam.® 
By mixing with an equal weight of Australian coal we ob- 
tained very satisfactory results. The calorific value as shown 
by the above analysis is equal to 70 per cent of that of the 
Australian coal used, while the average evaporation for it alone 
was but 60 per cent of that for Australian coal. The evapora- 
tion for three consecutive trials, in which a ratio of 1:1 between 
Australian and Batan coal was maintained, was slightly more 
than 70 per cent, which is the theoretical value for the coal. 
It may be true that the Australian coal itself burns slightly 
more economically by being thus mixed. 
Certain Japanese coals give entire satisfaction when fired under 
our boilers; Batan coal mixes well with these and gives results 
as satisfactory as with Australian coal. .Other Japanese coals 
have so fusible an ash that, with the rapid combustion and 
consequent high furnace temperature continuously maintained 
under boilers operated at full or over-load, it fuses and even- 
tually closes the air spaces in the grate. This entails a certain 
amount of labor in keeping the grate free, with a consequent 
loss of heat during the working of the fires. For this reason 
the coal in question can be used satisfactorily only under boilers 
operated at a light load. I made an unsuccessful attempt to 
find a mixture of one of these coals with that from Batan, which 
we could operate with the usual grate surface. Light firing 
would not generate sufficient steam, and heavy firing of any 
one of the mixtures caused it to cake so badly that it became 
inefficient. With sufficient grate surface the Japanese coals 
with fusible ash, mixed in any proportion with that from Batan 
Island, burned satisfactorily with an average reduction of over 
10 per cent of combustible matter in the ash of the Batan coal 
and a proportional increased evaporation such as was to be 
expected from the greater calorific value of the foreign coal, but 
no more grate is needed to burn Batan coal alone. From the 
standpoint of heat value, the only gain by mixing a small 
percentage of this class of Japanese coal with that from Batan 
Island is the reduction of the percentage of combustible matter 
® We have since doubled the grate surface, that is, used two boilers where 
one was sufficient with Australian coal, and find that under these conditions 
Batan Island coal is satisfactory. With an under-load a boiler can be ope- 
rated efficiently on this fuel for long periods with the production of prac- 
tically no smoke. 
