te 54: Teesdale, Clyde II.: The absorption of creosote by
the cell walls of wood. Cir. 200, U. S. Forest Service, 1912, p.
7.]

Soaking in kerosene seems to have no significant weakening
effect.[55]

[Footnote 55: Tiemann, H.D.: Effect of moisture upon the
strength and stiffness of wood. Bul. 70, U. S. Forest Service,
1907, pp. 122-123, tables 43-44.]

PART III TIMBER TESTING[56]

[Footnote 56: The methods of timber testing described here are
for the most part those employed by the U. S. Forest Service.
See Cir. 38 (rev. ed.), 1909.]

WORKING PLAN

Preliminary to making a series of timber tests it is very
important that a working plan be prepared as a guide to the
investigation. This should embrace: (1) the purpose of the
tests; (2) kind, size, condition, and amount of material needed;
(3) full description of the system of marking the pieces; (4)
details of any special apparatus and methods employed; (5)
proposed method of analyzing the data obtained and the nature of
the final report. Great care should be taken in the preparation
of this plan in order that all problems arising may be
anticipated so far as possible and delays and unnecessary work
avoided. A comprehensive study of previous investigations along
the same or related lines should prove very helpful in outlining
the work and preparing the report. (For sample working plan see
Appendix.)

FORMS OF MATERIAL TESTED

In general, four forms of material are tested, namely: (1) large
timbers, such as bridge stringers, car sills, large beams, and
other pieces five feet or more in length, of actual sizes and
grades in common use; (2) built-up structural forms and
fastenings, such as built-up beams, trusses, and various kind of
joints; (3) small clear pieces, such as are used in compression,
shear, cleavage, and small cross-breaking tests; (4)
manufactured articles, such as axles, spokes, shafts,
wagon-tongues, cross-arms, insulator pins, barrels, and packing
boxes.

As the moisture content is of fundamental importance (see WATER
CONTENT, above.), all standard tests are usually made in the
green condition. Another series is also usually run in an
air-dry condition of about 12 per cent moisture. In all cases
the moisture is very carefully determined and stated with the
results in the tables.

SIZE OF TEST SPECIMENS

The size of the test specimen must be governed largely by the
purpose for which the test is made. If the effe