171. It frequently happens in framework that one piece is pressed against the side of another, and should the resistance which the latter offers to the force be insufficient, a degree of compression may take place that would produce considerable derangement, if not the total failure of the framing.

With the view of obtaining some information on this point the author prepared two pieces of good Memel fir, and placing the end of one piece against the side of the other, he found that a pressure of 900 lbs. to the square inch produced only a faint impression, but with 1000 lbs. the impression became very distinct. Therefore, 1000 lbs. per square inch is the greatest force that should be applied transversely to yellow fir.

The resistance varies with the position of the annual rings, for in other trials the impression was very distinct with 950 lbs. With a load of 1400 lbs. per square inch the impression on English oak appeared to be about the same as was produced on Memel fir by 1000 lbs.; but the variation, owing to the position of the annual rings, was not so great.

172. The following Table by Mr. Hatfield shows the resistance of various woods used in America, to a pressure across the grain.*

Table XXVI

Kinid of Wood.

Specific gravity.

Force per square inch required to Crush the Fibres transversely 1/20th inch deep.

lbs.

Spruce...........................

.369

500

White Wood...................

.397

600

White Pine..........

.388

600

Hemlock..........................

.423

600

Chestnut..........................

.491

950

Ohio Pine ..........

.586

1250

Mahogany (Baywood)....................

.439

1300

Black Walnut ........

.421

1600

Georgia Pine.......................................

.613

1700

Oak ............

.612

1900

White Oak................................

.774

2000

Maple....................................

.574

2050

Locust..................................................

.762

2100

Ash ............

.517

2300

Hickory..........................................

.877

3100

Mahogany (St. Domingo)...............

.837

4300

Live Oak........................................

.916

5100

Lignum Vitae...................................

1.282

5800

173. It is obvious that the strength of a piece of framing is limited by the resistance of the parts which are pressed across the grain, and no greater force should be transmitted through any part which has its bearing on the side of another piece than the latter can support without being indented thereby.

* ' American House Carpenter.'