Manipulation:  Soon after cutting, each specimen will be weighed and its volume will be determined by the method described below.  The rings per inch and per cent summer wood, where possible, will be determined, and a carbon impression of the end of the specimen made.  It will then be air-dried in the laboratory to a constant weight and afterward oven-dried at 100 deg.C.  When dry, the specimen will be taken from the oven, weighed, and a carbon impression of its end made.  While still warm the specimen will be dipped in hot paraffine.  The volume will then be determined by the following method: 

On one pan of a pair of balances is placed a container having in it water enough for the complete submersion of the test specimen.  This container and water is balanced by weights placed on the other scale pan.  The specimen is then held completely submerged and not touching the container while the scales are again balanced.  The weight required to balance is the weight of water displaced by the specimen, and hence if in grams is numerically equal to the volume of the specimen in cubic centimetres.  A diagrammatic sketch of the arrangement of this apparatus is shown in Fig. 51.

[Illustration:  FIG. 51.—­Diagram of specific gravity apparatus, showing a balance with container (c) filled with water in which the test block (b) is held submerged by a light rod (a) which is adjustable vertically and provided with a sharp point to be driven into the specimen.]

Air-dry specimens will be dipped in water and then wiped dry after the first weighing and just before being immersed for weighing their displacement.  All displacement determinations will be made as quickly as possible in order to minimize the absorption of water by the specimen.

STRENGTH VALUES FOR STRUCTURAL TIMBERS

(From Cir. 189, U.S.  Forest Service)

The following tables bring together in condensed form the average strength values resulting from a large number of tests made by the Forest Service on the principal structural timbers of the United States.  These results are more completely discussed in other publications of the Service, a list of which is given in BIBLIOGRAPHY, PART III.

The tests were made at the laboratories of the U.S.  Forest Service, in cooperation with the following institutions:  Yale Forest School, Purdue University, University of California, University of Oregon, University of Washington, University of Colorado, and University of Wisconsin.

Tables XVIII and XIX give the average results obtained from tests on green material, while Tables XX and XXI give average results from tests on air-seasoned material.  The small specimens, which were invariably 2” X 2” in cross section, were free from defects such as knots, checks, and cross grain; all other specimens were representative of material secured in the open market.  The relation of stresses