Current Literature. 103 



been issued and they present data in regard to the number of 

 second growth hardwood trees required to make a cord ; kimber 

 and cordwood equivalents ; compound interest made by a log ; 

 shipping weights in pounds per 1,000 B. M. ; effect of moisture on 

 strength of timbers ; wholesale lumber prices, 1882-1908, New 

 York market ; approximate average rate of growth for northern 

 forests ; approximate current annual increase in per cent, of 

 volume for trees of different diameters when the average 

 number of rings in the last radial inch is known. 



Data upon the lumber industries of the state are being gathered 

 and those of three counties are included in the present report. 



C. D. H. 



The Physical Structure of Wood in Relation to its Penetra- 

 bility by Preservative Fluids. By Harry D. Tiemann. Reprint 

 from Bui. 120, American Railway Engineering and Maintenance 

 of Way Association. 1910. Pp. 16. Illustrated. 



This paper embodies the results of research to determine effect 

 of condition of wood on its permeability to gases and liquids ; 

 more especially the physical changes in the wood elements during 

 seasoning which affect their permeability. 



Every cell in fresh green wood is completely separated from 

 neighboring cells by the primary wall — middle lamella — which is 

 continuous. Water may percolate through this membrane 

 gradually but even under high pressure the rate is slow. The 

 membrane is practically impermeable to gases, regardless of the 

 pressure. This explains why green timber cannot be successfully 

 impregnated with preservatives. 



Seasoning of wood, whether naturally or artificially, effects 

 changes other than loss of moisture. One of great importance is 

 the opening up in the walls of the wood elements — tracheids, 

 fibers and vessels — of long narrow slits, visible only under high 

 magnification and appearing to run always spirally round the 

 cell. It is impossible to dry wood by any known method without 

 producing these slits, which increase in size as drying progresses, 

 and when once produced cannot be eliminated. It follows that 

 wood once dried cannot be restored -to its original condition. A 

 beamx dried and then soaked is always more brittle than the green 

 material. 



