96 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



The mean crushing strength of the two Japanese larch pit- 

 props from which the above standard specimens were cut was 

 1548 lbs., and of the two black Italian poplar was 1145 ^^s. 

 The compressive strength of the small standard specimens was, 

 therefore, rather more than double in each case that of the 

 pit-props. This fact must be borne in mind when comparing 

 the results obtained in this investigation with many of the 

 published results of British-grown soft woods, in view of the fact 

 that such tests were usually made on specially-selected samples 

 of the timber, free from all knots and other imperfections. For 

 this piece of research to have any real practical value, it was 

 essential to test the timber in the actual condition in which it 

 would be used in the mines. 



During the early part of the present year a few additional 

 tests of pit-props were carried out, the first being on three poles 

 of hybrid larch grown at Murthly, sent to the laboratory in June 

 192 1. When received these poles were quite green and in an 

 unfit condition for testing ; it was, therefore, decided to keep the 

 poles in the laboratory for a period long enough to ensure 

 complete seasoning ; they were, therefore, not tested till March 

 1924. The temperature of the laboratory is uniformly between 

 55° and 60° and there is good ventilation. The results are 

 given in the following table : — 



Hybrid Larch, grown at Murthly. 



The advantage of good seasoning of pit-props is well shown 

 when these results are compared with the mean figures given for 

 larch in the previous table, each of the three having a greater 

 strength than the mean figure for all the previous tests. 



While these tests were in progress, one specimen of Douglas 



