406 



Burr weighed 65'58 lbs., or 60*53 lbs. per cub. ft. But after 

 seasoning for two years the weights per cub. ft. were 31*29 

 and 35*69 lbs., respectively, the whole set averaging out at 

 32*96 lbs. per cub. ft. The 6 in. x 4 in. pieces of Pinus 

 canariensis weighed. on the average 65*42 lbs., or 60*4 lbs. per 

 cub. ft. on receipt at the Laboratory, but reduced finally to 

 41*83 lbs. per beam, or 38*61 lbs. per cub. ft. Some of the 

 insignis beams from Mount Burr contained as much as 158 

 per cent., of moisture, calculated on the dry weight of the 

 timber, but the moisture contents of all the timbers had fallen 

 to about 11 or 12 per cent, by March, 1919. 



Even when dried to approximately the same percentage 

 of moisture contents there was a considerable difference in the 

 weights per cub. ft. of the timber from the three trees from 

 which the insignis beams were cut, and an analysis of the 

 results of the tests on the seasoned wood shows that this 

 difference in weight was accompanied by a corresponding 

 difference in strength. With the notable exception of the 

 beam tests for the 20-year-old tree from Wirrabara the 

 strengths were very nearly proportional to the densities of 

 the timber, as the following table shows: — 



Ratios or Densities and Strengths of Pinus insignis. 

 Timber from Different Trees. 



From From 



Wirrabara. Mount Burr. 

 30 years 20 years 33 years 

 old. old. old. 



Ratio of densities ... ... 1 : : 



Ratio of strengths in compres- 

 sion along the grain ... 1 

 Ratio of shearing strengths ... 1 

 Ratio of strengths of beams 1 



1*08 : 1*21 

 1*09 : 1*20 



0*91 : 1*17 



Similar results, however, were not found to apply to the 

 maritima tests. Here again the timber from Mount Burr was 

 considerably heavier than that from Wirrabara, both when 

 green and when seasoned : but the tests showed that the Mount 

 Burr timber was distinctly the weaker. Tested as beams the 

 ratio of the strength of the Mount Burr timber to that from 

 Wirrabara was 13 : 21, and in all tests except shearing the 

 denser timber was inferior to the other. Density is evidently 

 by no means the only factor in determining the strengths of 

 woods, even of the same species. 



The tests made upon the timbers comprised measurements 

 for shrinkage with seasoning, transverse tests carried out on 

 beams 6 ft. between supports and either 6 in. x 4 in. or 

 4 in. x 2 in. in section, shearing tests, and determinations of 

 the strength of the timber in compression both longitudinally 



