The external energy of the blow (_i.e._, the weight of the hammer X the height of drop) is compared with the energy used in static tests at equal amounts of compression.

For instance: Energy delivered, impact test 35,000 inch-pounds Energy computed from static test .26,400 " " Efficiency of blow of hammer .75.3 per cent.
_Preparing the material_: The material used in making impact tests is of the same size and prepared in the same way as for static bending and compression tests.

Bending in impact tests is more commonly used than compression, and small beams with 28-inch span are usually employed.
_Method_: In making an impact bending test the hammer is allowed to rest upon the specimen and a zero or datum line is drawn.

The hammer is then dropped from increasing heights and drum records taken until first failure.

The first drop is one inch and the increase is by increments of one inch until a height of ten inches is reached, after which increments of two inches are used until complete failure occurs or 6-inch deflection is secured.
The 50-pound hammer is used when with drops up to 68 inches it is reasonably certain it will produce complete failure or 6-inch deflection in the case of all specimens of a species; for all other species a 100-pound hammer is used.
_Results_: The tracing on the drum (see Fig.