356 
Philippine Journal of Science 
1919 
Thus the durability or resistance of timbers to the attack of 
termites is not effected by hardness or weight; that is, the im- 
munity of timbers is not due to their physical properties. 
RELATIONSHIP BETWEEN THE RESISTANCE AND THE CHEMICAL 
PROPERTIES OF TIMBER 
Snyder 7 states that the immunity or relative resistance of 
ironwood is not due to hardness — since Asiatic termites attack 
the hardest wood, lignum-vitse — but to the presence in the wood 
of a substance (oils or alkaloids) repellent or distasteful to 
termites. lie also states that the presence of tyloses or of gums 
may be factors in determining the durability and resistance of 
hardwood species. It has been proved that the physical prop- 
erties of woods are not the real factor of resistance as suggested 
by that author. However, another suggestion of Snyder, that 
the presence of certain chemical substances in woods is the 
true factor, is somewhat dubious. As he gives no data in detail, 
it is hard to understand what are the principal ingredients and 
how they act in preventing the damage. 
In order to determine the relationship between the resistance 
and the chemical properties of woods, I made the following 
investigation : 
The quantity of ash and benzene extract in the above-men- 
tioned woods was measured and compared with the percentage 
of damage obtained at Tainan. 
Sampling. — A block of wood is cut along the three planes 
crossed at right angles, and the sawdust is collected. By the 
diagonal method reduction of the amount of the sample is made 
repeatedly, until about 20 grams of the sawdust are obtained. 
This sample is exposed for one hour in an air bath at 105° to 
110° C. Then it is kept in a desiccator as a representative 
sample. 
Method of estimation of ash. — A 1-gram sample is heated to 
redness in a platinum crucible over a Bunsen burner, and the 
incombustible substances are brought to a constant weight. 
Method of estimation of benzene extract. — To estimate the 
benzene extract 5.00 grams of the sample are put into a Soxhlet 
apparatus and extracted with pure benzene for from six to 
ten hours. The benzene is driven off on a water bath, and 
afterwards the container is heated in an air bath at 120° C. 
to a constant weight. All determinations are made in duplicate. 
7 Bull. U. S. Bur. Ent. 94 (1916) 79, 80. 
