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.