474 Philippine Journal of Science 1919 
is built in a zigzag form below the hearth and extends across 
the width of the furnace. From the plan it may be seen that 
this furnace belongs to the gas-producer type, for the combus- 
tion in the fire chamber is incomplete. The heat radiating from 
the hearth preheats the air passing through the zigzag passage 
before it mixes with the hot gases in the combustion chamber. 
The result is that a more complete combustion of the gases takes 
place, and a higher temperature is obtained from the flame 
around the crucible. The peep hole c, which is covered with 
a sheet of mica, permits the operator to observe the temperature 
around the crucible and also enables the removal of any soot 
that may have accumulated along the passage from the crucible 
chamber to the chimney. When slot b is obstructed, the door 
d permits the cleaning of the passage from the fire grate to the 
combustion chamber. 
The operation of this furnace is very simple. After the fire 
has been started, sufficient coal is piled in the fuel chamber to 
fill it to the door level. The height of the fuel bed is kept at a 
constant level by feeding the fire chamber with 1 to 2 kilograms 
of coal every fifteen to twenty minutes, and occasionally cleaning 
the grate to avoid accumulation of cinders. If the temperature 
around the crucible decreases, it is an indication that the quan- 
tity of coal burning in the fire grate is insufficient; that too 
much or too little air is being admitted through the air passage 
a or in the fire grate; or that the passage from the crucible 
chamber to the chimney is obstructed with soot. This furnace 
gives a temperature sufficiently high to expel the gas bubbles 
from the molten glass and, besides being economical in fuel, 
has the additional advantages of simple construction and easy 
operation. 
If a glass factory is to be established in the Philippine Islands, 
the following facts should be taken into consideration: 
The quality and price of fuel available are as important fac- 
tors as are the raw materials to be melted. At present the 
market price of coal in Manila varies from 40 to 50 pesos per 
metric ton, depending upon the quality and the market condi- 
tions. With such a high price for coal, it may prove advanta- 
geous to use coconut shells when practicable. This fuel can be 
obtained in commercial quantities at from 8 to 10 pesos per 
metric ton. : 
Labor is also an important factor. Glass making is a new, or 
practically unknown, industry in the Philippines, and naturally 
there are few glass blowers in the Islands. If a factory with 
