372 



Philippine Journal of Science 



All the blocks treated with 1 per cent solution were seriously 

 attacked after the lapse of six months. The blocks that were 

 treated with 2 and 3 per cent solutions were also seriously- 

 attacked, although a small number of them remained in sound 

 condition for more than two years. By the last inspection it 

 was found that the percentage of damage was very much lower 

 in the blocks treated with 5 per cent and 10 per cent solutions 

 than in those treated with 1 and 3 per cent solutions. 



There is no doubt that the camphor green oil itself is effective 

 in preventing the attack of termites. However, when it is used 

 in a too diluted condition it is not absolutely effective, the per- 

 centage of damage being inversely proportional to the amount 

 of the oil contained in the solution. 



Table XXVIII. — Damage done by termites to Japanese -pine blocks treated 

 with different percentages of camphor green oil solution. 



• Length of exposure to termites. 



Percentage of damage to blocks containing— 



1 per cent 

 of oil. 



2 per cent 

 of oil. 



3 percent 

 of oil. 



5 per cent 

 of oil. 



10 per 



cent of 



oil. 





100 



89 

 90 

 94 

 94 



7G 

 90 

 90 

 90 



19 

 44 

 49 

 53 



• 7 

 M 

 37 



46 

















The amount of the oil that is effective in preventing the 

 damage may vary with different kinds of timber. I regret 

 that at present I am unable to show the exact amount of oil 

 applicable to different Japanese timbers. 



Experiment 3. — From an economic point of view, it is desir- 

 able to use a minimum amount of the camphor green oil; 

 therefore, the discovery of an economical, efficient solvent in 

 making a dilute solution of the green oil becomes a most im- 

 portant problem. For this purpose I have selected a neutral 

 oil of petroleum produced from the crude oil obtained at Niizu, 

 Japan proper, because it is produced in large quantities at a 

 reasonable price; it is almost colorless, giving no stain to 

 timbers ; and it is highly effective in killing the termite. 



The following is the result of the test made to determine the 

 exterminating power of various neutral oils. A small amount 

 of oil was placed in a watch glass and a worker of Coptotermes 

 formosanus was immersed. Under a dissecting microscope the 

 motion of the insect was observed and the time at which it 

 became motionless was recorded. 



