PERMEABILITY OF WOOD TO AIR 



195 



Now cut a few centimeters from each end and fasten the end 

 of the branch originally uppermost to a glass tube 6 cm. in 

 length by means of a section of pressure tubing (rubber). Now 

 connect the glass tube with an air pump, or filter pump, and dip 

 the lower end of the twig in a 

 solution of ferric oxychloride. 

 This may be made by adding 3 

 parts of water to 1 of the officinal 

 preparation of liquid ferri oxychl- 

 orati, which may be procured of 

 pharmacists. Exhaust the air 

 from the upper end of the branch. 

 If the fluid exuding from the 

 branch, a quarter of an hour later, 

 is colorless, cut away a few centi- 

 meters from the lower end of the 

 branch and immerse the newly 

 cut surface in the liquid. Repeat 

 at same interval until the brown 

 fluid appears at the upper end of 

 the branch. The length of the 

 branch when this occurs gives the 

 maximum extent of free air com- 

 munication in the vessels. The 

 liquor is colloidal and may not be 

 forced through membranes. If 

 the first test has been performed 

 with a twig two years old, repeat 

 with one of the same species five 

 or six years old, and note the increased length of the free air 

 communication. The results will be approximate. 



269. Permeability of Wood to Air. Make some rods of wood 

 from the outer portion of newly -felled trees of Abies, or Taxus, 

 which are entirely free from dry rot, and insert the short arm of 

 one end in a U-tube and seal tightly with wax. The long arm 



Fig. 96. Demonstration of the 

 length of air-passages in woody stems. 

 a, filter pump attached to water tap. b, 

 large glass tube in the lower end of 

 which is fixed a branch of chestnut, 

 standing in a dish containing coloring 

 fluid, or injection material. After 

 Belzung. 



