EXPERIMENT OF THE ELECTRIC RESISTANCE IN WOOD 



By JUJIRO HIRUMA, Forest Expert 



It is generally known that wood offers great resistance to the 

 electric current but the resistance in no small degrees, is influenced by 

 the quantity of moisture contained in the wood. Wood is since long time 

 looked upon as an imperfect insulator but no experiment has been tried 

 to determine its resistance. 



The experiments undertaken by me to determine the resistance of 

 wood to the electric current were tried on different species of wood in 

 regard to the disposition of wood tissues, amount of moisture content and 

 specific gravity. 



I. Apparatus used for the Determination 



Meg-ohm Normal Resistance Box; D'Arsonval's Galvanometer and 

 Shunt. 



II. Connection of Electric Poles with the Wood to be Tested 



To ensure the close contact of electric poles with the wood to be 

 tested, copper plates, copper gauze and tin-foil were first used. The 

 experiments showed, however, that the resistance varied according to the 

 amount of the different pressure used in bringing these materials in 

 contact, thereby giving rise to apparent irregularities in the resistance 

 of the wood. We, therefore, used mercury instead of the materials above 

 named, and perfect contact was secured so that no irregularity arose. 

 One end of the wood to be tested was dipped into a vessel filled with 

 mercury while the other end was wrapped with insulating tape or fitted 

 with a projecting wooden frame into which mercury was poured in. 

 The two electric poles were then inserted in the upper and lower vessels 

 of mercury. 



III. Electro-motive Force 



In the case of high resistance, the voltage should generally be equal 

 to or twice or thrice as great as that which used for the material to be 

 tested in practical use. 



