Periodical Literature. 101 



The author proposes certain standard ratios of fibre strain in 

 relation to speed for compression, bending and shearing tests. 



C. D. H. 



The effect of the speed of testing upon the strength of wood and the 

 standardisation of tests for speed. Reprint from Proc. American Society, 

 Testing Materials. 1908. 



Janka, of the Austrian Experiment Station, 

 Hardness reports on a series of hardness tests with 



of his improved ball test, (an improvement 



Wood. over Brinell's method with metals) in which 



one-half iron ball, the area of the largest of 

 which is one square cm, hence its radius 5.462 mm, is pressed 

 into the wood until fully imbedded, when the pressure employed 

 is a direct expression of hardness. A parallel series tested with 

 a cone impression gave invariably lower results, due according to 

 the author to the splitting effect of the cone which called into 

 requisition the cleavability and in part elasticity rather than hard- 

 ness. Practically, however, this hardness test by cone corres- 

 ponds to that of a nail or screw, but more important is the re- 

 sistance to saw, file, plane, knife, axe, chisel, etc. The author 

 thinks that owing to the impossibility of devising special tests 

 for all these uses of tools, the "neutral" tests with ball as devised 

 by him most satisfactory. 



A tabulation of the comparative tests by cone and ball show no 

 parallelism, but in general broadleaf wood was more resistant to 

 the cone than coniferous wood, when tested on the cross cut face, 

 not on length sections, the different cleavability in the first case 

 furnishing the explanation. The hardness of spruce and fir, when 

 tested with ball on the cross section was to that tested on the 

 length sections, about as 100:60. 



The law of relation between hardness and specific gravity which 

 for the same species was well maintained, did not appear so well 



XT 



from species to species. This relation -q- was considerably smaller 



in coniferous than broadleaf wood i. e. the latter in proportion to 

 its weight is harder. 



That the hard summer wood of the pine and larch in tests on 

 length sections would increase resistance is only natural, hence 

 the difference of hardness of cross section and longitudinal sec- 



