230 Forestry Quarterly. 



The "hardness quotients" for the woods lie between S.5 (pahn) and 

 13.7 (ebony). Comparing these quotients with the "relative quan- 

 tity quotients", i. e., Compression strength, a very considerable dif- 



Specific Aveight 

 ference appears. In conifers the hardness quotient is smaller than 

 the quantity quotient, the reverse in broadleaved wood; for instance, 

 for spruce the two quotients are 6.7 and 9-1 respectively; for oak, 

 9.8 and 5.1. Hence the latter are better where resistance to shock 

 and wear is required, the conifers better for building purposes, 

 where the relation of strength to weight is to be most favorable. 



From this consideration it follows that influences other than hard- 

 ness determine compressive strength, hardness probably depending 

 on coherence of fibres sideways, compressive strength on stiffness, or 

 resistance to binding of fibres. From the specific weight of different 

 species of woods no final conclusion as to their hardness or strength 

 is possible. 



Lastly, the author brings forward as germane to the hardness 

 tests, a series of tests on the resistance to the penetration of an axe, 

 made with an axe-like wedge of 6 cm. width, made to penetrate 2 

 cm., on bolts free from knots 10 cm. thick and 50 cm. long, which 

 are tested green and dry in two directions. The lengthwise test 

 could be made only on green wood, since on dry specimens the wood 

 would invariably split. 



It was shown that here again moisture produces a considerable 

 diminution of resistance; that is to say, wet wood splits easier, 35 

 per cent, in coniferous w^ood and in length direction of broadleaf, 26 

 per cent, in the cross grain direction of the latter. 



The relation to specific strength was not clearly shown by the 

 tests. To drive the axe across the fibre into coniferous wood re- 

 quired about double the force needed for doing so lengthwise, for 

 the tested broadleaf wood somewhat less than double. The soft 

 conifer wood, spruce, fir, pine, showed pretty nearly the same resist- 

 ance radially or tangentially, but the broadleaved woods showed ra- 

 dially much less resistance than tangentially. The failure of the 

 tests on the cross-section of the latter by splitting called attention to 

 the ease with which the latter split radially, i. e., in the direction of 

 the pith rays, and also to the toughness (in these tests) of the 

 conifers. 



A large number of tables and diagram.s bring out the detail of this 

 instructive series of tests. 



Die Hdrte des Holzes. Centralblatt ftir das gesammte Forst- 

 wesen. May, June, 19O6, pp. 193-202, 241-260. 



