TIMBER: ITS STRENGTH, AND HOW TO TEST IT. 15 
Cross Breaking Stress per square inch, tn lbs. 
: Mean 
. Kind of Wood. Maximum. Minimum. Mean. Modulus of 
Elasticity. | 
| 
Spruce, . , : Sa et a | 2, 88 I, 330,000 
Mien eA 75 994 4,093 339; 
Yellow Pine, . : : = PLEE;300 | | “3,962 7,239 | 1,744,000 
(Pinus echinata). | | 
Oaks. : ; 2 ; 7,660 4,985 | 6.074 | 1,292,000 
| (Quercus alba). 
| White Pine, . ‘ : silk Ja25o 3437 4,807 | 1,080,000 
(Pinus Strotus). 
Professor Johnson’s experiments upon cross bending for the 
Forest Department research were made upon beams 4 inches 
square, and tested upon a 6 foot span; and, in his investigation, 
great care was taken to arrange the load in such a way that 
it increased gradually, and increased the deflection gradually, 
at a rate of about + inch per minute, until the final rupture point. 
There is no doubt whatever that different results can be 
obtained in cross-bending tests of timber by varying the rate 
at which the load is applied. This is a fact well known, of 
course, to all experimenters, and is true not only of timber, but 
of all other materials. 
The next Table gives the results obtained by Professor Johnson, 
and I have collected into this Table not only the cross-bending 
stresses, but the crushing strength, both endwise and across the 
grain, and also the shearing strength of the timber. 
Cross Breaking Stress per Crushing >tress Sh 
Weight square inch. Lbs. persq in. Lbs. Ena 
Kind of Wood. Sp. gr. | Pei. ] in Ibs. 
| foot. | Limit of | Final | Modulus of | End- | 4.0... | POS? 
Elasticity.| Load. Elasticity. | wise 5 : 
4 | Ibs. 
Long-leaf Pine, .| o61 38 10,000 | 12,600 | 2,070,000 | 8,000 | 1,260} 835 
(Pinus palustris). 
Red Pine, . =| O750,| 31 7,700 | 9,100 | 1,620,000 | 6,700} 1,000} 500 
(Pinus resinosa). 
White Oak, . . | 0°80 | 50 9,600 | 13,100 2,090,000 | 8,500 | 2,200 | 1,000 
(Quercus alba). 
White Elm, . IMO s4cl 34 7,300 | 10,300 | 1,540,000 | 6,500} 1,200| 800 
(Ulmus americana).| 
All these results have been reduced to 12 per cent. moisture conditions. 
In order to give some idea of the great variation in the 
strength of timber, I may say that in these tests, out of one 
hundred samples of the same kind of timber, 54 per cent. of 
