54 
Tests upon the crashing strength (tensile and transverse) of different 
specimens of the same species of wood show that there is a quite con- 
stant ratio between each and the specific gravity, thus agreeing with 
what has been stated as to the presence or absence of certain dense 
cells in the microscopical structure of the layers. So that one who is 
skilled, with the aid of a iniscroscope, can make a very close estimate of 
the comparative suitability of different pieces of wood for definite pur- 
poses. As a case in point, a railroad company, doing a heavy freight 
business, being able to buy cedar ties for one-third the cost of oak, for 
this reason put them down, but only to find that after they had injured 
one set of rails these ties were too soft for their heavy traffic. Ami. 
croscopical examination of the timber would have enabled one to predict 
what the result would be and to save the expensive trial. 
Table IV. shows the ratios between the longitudinal crushing strength 
and the specific gravity of the woods under consideration. The ratios 
are obtained by dividing the crushing weight per square inch by the 
specific gravity, which gives a ratio representing the crushing weight 
of a square inch having a specific gravity of one. The average for 
White Oak, as given in the table, is 9,923 pounds, which for practical 
purposes might be called 10,000 pounds. If we compare oak grown 
south of the fortieth parallel, the result will be 10 per cent, higher. 
Having another piece of oak, the specific gravity of which is 0.6578, 
and wishing to know its approximate crushing weight, we obtain it by 
multiplying its specific gravity by 10,000, which gives 6,578 pounds. 
The same method applies to other woods. 
Comparing one wood with another, taking White Oak as unity, the 
comparative crushing strength of Chestnut is 1.3 per unit of specific 
gravity; White Cedar, 1.07; Yellow Pine, 1.25; Hemlock, 1.3; West- 
ern Larch, 1.55 ; Tamarack, 1.38. The crushing strength given in 
the table is for blocks eight diameters in length. For larger ones the 
strength would be less. In using them a factor of safety must be 
adopted most suitable for the work. The table gives data which, to a 
great extent, can be used to determine the proper size of columns of one 
wood to be substituted for another, by giving the proper dimensions and 
retaining approximately the same factor of safety, a matter which has 
been neglected in too many cases. 
Table V. — Resistance to Indentation.* 
[Pressure in pounds per square inch for indentations of one twenty-fifth of inch.| 
Woods. 
Pressure. 
251 
290 
329 
380 
387 
401 
402 
White Oak 
Chestnut 
White Cedar 
Yellow Pine ... 
Hemlock 
Tamarack 
Western Larch 
2, 974 
1, 446 
878 
2, 637 
1,359 
1,265 
2, 271 
*From tho Tenth Census Pveport, Vol. IX., 1880. 
