The average weight in Ibs. per cubic foot = 37.8. 



'' co efficient of elasticity in Ibs. per sq. in. = 754,000. 



" uiaxiiniini skin stress " " =8,300. 



safe working skin stress in Ibs. per sq. in.. .'} being at 



factor of safety = 1100. 



Further experiments will probably show that these data require some 

 modification. In fact, the actual skin stress and co-efficients of elast- 

 icity are certainly greater than those given in the preceding table, 

 which have been calculated <ai the as.-umption that the amount of the 

 compression at the central support is sufficiently small to be disregarded, 

 but it has been shewn, as for example, in the case of Beam XLIX, 

 that the skin stresses are largely affected by this compression. The 

 co-efficients of elasticity areaho necessarily increased by the diminution 

 in the effective depth. Similar remarks apply to the other timbers. 



From the experiments with the old White Pine stringers, it might 

 be inferred that these timbers have lost considerably in weight, but 

 that they have in a great degree retained their strength and stiffness. 

 Other old Timbers will require to be tested, however, before any definite 

 statement can be made on ihe subject. 



NEW SP.RUCE BEAMS. 



Beam LIV was tested Nov. 2nd, 1893, with the annular rings as in 

 Fig. 106. 



This stick was sent to the laboratory by Mr. T. J. Claxton. It was 

 cut out of a tree felled near the Skeena Eiver, Britisli Columbia, on 

 the Pacific Coast, about six hundred miles north of Victoria. The log 

 was felled in Dec., 1892, or January, 1893, and was over 100 ft. in 

 length, squared 36 ins. at the small end, and would have provided from 

 12,000 to 15,000 of market lumber. 



The beam in question was sawn from the log in June, 1893, and was 

 shipped by steamer at the end of June from the town of Claxton, situ- 

 ated at the mouth of the Skeena River, where the mills are located. 

 At Victoria il.c beam was transhipped and brought down in August 

 via the C.P.R. to Montreal. It was delivered at the laboratory early 

 in September. 



It might, perhaps, be of interest to note that the cost of freight for 

 this beam from Ulaxton to Victoria was 4.00 ; from Victoria to Van- 

 couver $2.00 ; from Vancouver to Montreal $46.00 ; and the cartage 

 to the University 4 00, making a total cost of freight of 56.00. 



It is said that the spruce from the Skeena District is of a specially 

 fine quality, having a clear straight grain, and possessing a large amount 

 of toughness. 



The load upon tlic beam was gradually increased until it amounted 

 to 36,800 Its., when the beam failed by the crippling of the fibres on 

 the compression side, Fig. 1 07. 



The maximum skin stress corresponding to this breaking load 

 5908 Ibs. per square inch. 



The total compression of the material at the central support was .5- 

 in., so that taking the effective depth as 17 ins., the maximum skin 

 compressive stress is 5941 Ibs. per square inch, the corresponding skin 

 tensile stress being U301 Ibs. per square inch. 



If it is assumed that the usual law holds good for the whole of the 

 effective depth of 17 ins., the maximum skin stress is 6260 Ibs. pel- 

 square inch. 



The co-efficient of elasticity, as deduced from an increment in the 



32 



