TIMBER FOR AEROPLANE AND PIT-PROP PURPOSES. 



95 



It has been pointed out earlier in this paper that it was very 

 difficult during war years to obtain really representative samples 

 of the various woods selected for testing, hence in comparing 

 the relative compressive strength of home and foreign-grown 

 timber it would be wiser to neglect the results of the 1918 tests ; 

 if this is done we obtain the following results for the important 

 home-grown species : — 



It will be seen that the strengths of the three home-grown 

 timbers — larch, spruce, and Scots pine — are very close to that 

 obtained in the tests of the foreign-grown Finnish red wood. 



While the 1918 tests were being carried out, it was decided to 

 make some attempt to determine the relation between the com- 

 pression strengths of timber in the form of pit-props and the 

 compressive strength of the same timber as determined by 

 testing small standard specimens (see vol. xxxvi. p. 60). These 

 standard specimens were prepared from short lengths cut from 

 selected pit-props before these props were tested ; two props of 

 Japanese larch and two of black Italian poplar were used for 

 this purpose. Standard specimens were turned from a block of 

 wood cut from the central part of the cross-section of the prop, 

 and also from a block near the edge of the cross-section. The 

 results obtained are given in the table below : — 



The "A " specimens were from the middle of the cross-section of the prop. 

 The "B" specimens were from the edge of the cross-section of the prop. 



