18 



cox. 



account of the vaporization of this water. The crackling observed during 

 the combustion of some woods may be explained on this basis. The 

 popping of soft M'oods might be explained by the contained water being 

 converted into steam whereupon the wood explodes, not being able to 

 resist the strain. A large quantity of alkaline salts which are quite 

 easily volatilized occur in the mangrove ash. Common salt (sodium 

 chloride) melts at 8"20°. "WTien mangrove woods are burned a large 

 quantity of the ash is volatilized, which condensing on the walls of the 

 furnace gradually builds up a clinker. Mangrove wood grown in the 

 edge of the salt water was burned at the plant of a mining company in 

 Masbate. It was found after a time that the furnace walls were clinkered 

 badly. A specimen of this clinker, which is very saline, presented to me 

 by Mr. Boag is shown in the following figure. 



Fig. 1. — Furnace clinker formed when mangrove wood was burned. 



The sample left on a cupboard shelf in my laboratory since September, 

 1907, over three years ago, shows crystals of sodium chloride due to 

 efflorescence. The subject of volatile ash is Avorthy of special considera- 

 tion, inasmuch as wood of this character used in the burning of pottery 

 would materially influence the character of the glaze, or the glaze on 

 crude pottery- might be controlled by carefully selecting the firewood. 



