242 The Philippine Journal of Science im 



purpose by several of the smelters is the residual clay which 

 results from the decomposition of the granite. A chemical 

 analysis of this clay appears in Table XI, page 254. Before 

 each smelting-run the sides of the crucible and runner are lined 

 or veneered with a mixture of clay and charcoal. 



A feature of the furnace which is essential to successful smelt- 

 ing is a quartz-sandstone block 20 by 30 by 40 centimeters in 

 size which is set in the wall of the crucible over the tap hole 

 just where the blast, entering through the tuyere from the 

 opposite side, will impinge upon it. This stone, which the Fili- 

 pinos call bato buga, is more refractory than the furnace clay, 

 and resists the highest temperature of the furnace at a point 

 where without it the furnace wall would be quickly eaten 

 through. These refractory stones for all the furnaces are ob- 

 tained from the bedded quartz-sandstone at the base of the sedi- 

 mentary series near the barrio of Bayabas. 



The tuyere (bombon) is a tube 60 centimeters long, 6 centi- 

 meters in interior diam.eter, and 20 centimeters in exterior di- 

 ameter, which is made of unbaked furnace clay. 



The blowing apparatus {joncoy) is a hollow log, 35 centi- 

 meters in interior diameter and 3.5 meters long ; it is fitted with 

 a wooden piston which is edged with soft chicken feathers to 

 prevent the leakage of air around it. The piston rod is long 

 enough to permit a full stroke of the piston when worked back 

 and forth by hand. The blower is double acting, wooden tubes 

 conducting the blast from valves at both ends of the displacement 

 chamber to the tuyere. In operation the blower lies almost 

 horizontal, one end being raised slightly from the floor to facili- 

 tate the work of the operator. 



The molds {hormas) are made of clay reenforced by rattan 

 or occasionally by wire. Each mold consists of a base, which is 

 fixed rigidly to a frame or rack, and a removable cover. One 

 end of the frame rests always on the ground, but the other end 

 can be raised to a seat on two crotched sticks so that the molds 

 when in position to receive the metal are inclined at a convenient 

 angle, about 40° from the horizontal, for pouring. The frames, 

 together with the small posts upon which the raised ends rest, 

 are called horses (caballos), and the usual equipment for a 

 smelter includes a train of about 15 horses, 3 mounted with 

 large single plowshare molds and the rest carrying each a pair 

 of smaller plowshare or plowpoint molds. 



Charcoal burning. — An essential attribute of the smelter is the 

 cluster of charcoal kilns which surrounds it. There are some- 



