_Making the test_: After the specimen is fitted in the machine the load is applied continuously at the rate of 22° per minute. A troptometer is used in measuring the deformation. Readings are made until failure occurs, the points being entered on the cross-section paper. The character of the failure is described. Moisture determinations are made by the disk method. _Results_: The conditions of ultimate rupture due to torsion appear not to be governed by definite mathematical laws; but where the material is not overstrained, laws may be assumed which are sufficiently exact for practical cases. The formulæ commonly used for computations are as follows: 5.1 M (1) T = ------- c^{3} 114.6 T f (2) G = ----------- a c a = angle measured by troptometer at elastic limit, in degrees. c = diameter of specimen, inches. f = gauge length of specimen, inches. _G_ = modulus of elasticity in shear across the grain, pounds per square inch. M = moment of torsion at elastic limit, inch-pounds. T = outer fibre torsional stress at elastic limit, pounds per square inch. SPECIAL TESTS _Spike-pulling Test_ Spike-pulling tests apply to problems of railroad maintenance, and the results are used to compare the spike-holding powers of various woods, both untreated and treated with different preservatives, and the efficiency of various forms of spikes. Special tests are also made in which the spike is subjected to a transverse load applied repetitively by a blow. For details of tests and results see: Cir. 38, U.S.F.S.: Instructions to engineers of timber tests, p. 26. Cir. 46, U.S.F.S.: Holding force of railroad spikes in wooden ties. Bul. 118, U.S.F.S,: Prolonging the life of cross-ties, pp. 37-40. _Packing Boxes_ Special tests on the strength of packing boxes of various woods have been made by the U.S. Forest Service to determine the merits of different kinds of woods as box material with the view of substituting new kinds for the more expensive ones now in use. The methods of tests consisted in applying a load along the diagonal of a box, an action similar to that which occurs when a box is dropped on one of its corners. The load was measured at each one-fourth inch in deflection, and notes were made of the primary and subsequent failures. For details of tests and results, see: Cir. 47, U.S.F.S.: Strength of packing boxes of various woods. Cir. 214, U.S.F.S.: Tests of packing boxes of various forms. _Vehicle and Implement Woods_ Tests were made by the U.S. Forest Service to obtain a better knowledge of the mechanical properties of the woods at present used in the manufacture of vehicles and implements and of those which might be substituted for them. Tests were made upon the following materials: hickory buggy spokes (see Fig. 5); hickory and red oak buggy shafts; wagon tongues; Douglas fir and southern pine cultivator poles.