304 TIMBER 



Barlow, Laslett, and many others in this country, we owe 

 a great deal, since it was from the tests on small pieces of 

 timher made in a primitive manner, but with the best 

 means at their disposal and before the days of large testing 

 machines, that men had to deduce the scantlings required 

 for constructional work ; now, however, when better means 

 are available, endeavours should be made to produce results 

 which can be depended upon with something akin to the 

 reliance placed upon tests of steel, although there are 

 difficulties in connection with the testing of timber which 

 do not occur in the testing of steel. 1 



The amount of moisture in timber considerably affects 

 the result of tests, probably to a greater extent than any- 

 thing else. The drier the timber, the higher the results 

 obtained ; in other words, seasoned timber is stronger than 

 (/reen timber, and that to a very considerable extent, as will be 

 shown ; but in general it will be safer in making calculations 

 for strength of constructional timber to make use of the 

 tests for moderately seasoned wood, as it is not often that 

 highly seasoned timber is used ; it too often has to season 

 in the work. 



It is, therefore, useless making comparisons between tests 

 of timber unless we compare their conditions of moisture. 

 It takes a very long time by air seasoning to thoroughly 

 dry timber of large sizes. Two pieces of pitch pine 16 ft. 

 by 12 inches by 12 inches and 16 ft. by 16 inches by 8 inches, 

 after air seasoning for two years, showed that whilst in the 

 outer portion of the wood there was only 17 per cent, of 

 moisture, the inner portion still contained 25 per cent. ; - 



1 A number of tests on large-sized columns and beams of oak were 

 made by M. P. S. Girard in France so far back as 1798, but these tests 

 appear to have been lost sight of, and others of less value used. (See 

 Barlow's Strength of Materials, 1837.) 



2 Bulletin No. 70, United Status Dept. of Agriculture, p. 123. 



