UNIFICATION OF METHODS IN TESTING MATERIALS, XXXI. 
record accurately the effect of the shock would furnish most 
valuable information not merely on railway axles, tyres, and rails, 
but on nearly all materials used in construction ; they would give 
information which could not be obtained in any other way, and 
they offer a very promising field for scientific investigation. 
Superficial penetration and perforation by shock are recom- 
mended by the various Commissions, also tests of hardness by 
scratching and by resistance to wear and tear, but the methods 
most suitable have not been definitely decided. 
Torsion TEsTs. 
Torsion tests should be made with machines arranged in such a 
manner that all disturbing influences such as transverse stresses 
and longitudinal tension should be prevented. The test pieces 
and the collars or holders should be concentric cylinders, and 
keyways should be cut in the test piece at each end to secure it to 
the holders, which should be capable of sliding longitudinally 
when the piece is under stress. Very delicate observations on 
the elastic twist may be made by means of a telescope fixed to the 
test piece reading on to an upright scale placed at some distance 
from the telescope. Mixed tests (shearing and punching) are 
recommended by the Commissions for study—they say mild steel 
and ingot iron should not be punched. 
Folding, curving, and bending tests are recommended, in which 
Strips 250 x 40 millimetres are used, excepting in the case of 
Copper and its alloys, in which the length may be reduced to 150 
millimetres, The apparatus should be slow moving, and expose 
clearly the weakest portion of the test piece, and the bending 
Should be made round a mandrel 25 mm. in diameter. The test 
Pieces cut from plates should have a width of three times the 
thickness with rounded edges. One American society recom- 
mends that the diameter of the mandrel should be twice the 
thickness of the plate. 
These tests niay be made upon the material cold or heated to a 
Standard temperature, or after quenching from a red heat in water 
