XXX. W. H. WARREN. 
as nearly as possible in accordance with these conditions. In 
testing beams, axles and rails, the loads necessary to produce this 
elastic limit and commencement of the permanent deformation 
should be determined, as well as the elastic and permanent 
deflections. 
Impact Tests. 
The importance of impact tests are fully recognized by the 
various Conventions, and continued study in this direction is 
recommended. The standard weight of hammer adopted by the 
Conventions is 1000 kilogrammes, but in certain exceptional cases 
hammers of 500 kilogrammes are permitted. The striking sur- 
faces should be of forged steel, the vertical axis of the hammer 
should be perfectly symmetrical with the plane of the leads, and 
the guided length should be at least double the clear width 
between the guides. The weight of the anvil block shall be at 
least ten times the weight of the hammer, and the foundations 
shall be inelastic. The American Society however, recommend 
that the weight of the anvil block alone or embedded in solid 
masonary should form a solid mass of at least fifteen times the 
weight of the hammer. The leads should be lubricated with 
plumbago, and the frictional resistances should not exceed 2%. 
In order to determine the etfect produced by various heights of 
fall the work done by the hammer upon standard copper cylinders 
should be carefully studied. The maximum height of fall recom- 
mended is six metres. “A sliding scale should be used, arranged 
so that the zero coincides with the level of the top of the test 
piece. It has been suggested that a short flexible cord or chain 
should be fixed between the detaching device and the hammer. 
The point of suspension should be on the vertical axis passing 
through the centre of gravity of the hammer. Impact tests are 
used at present in connection with the testing of tyres and axles, 
also for rails, but the apparatus used is rough and the results 
necessarily inaccurate. At the same time they give a good, rough 
indication of the suitability of the material for the purpose 
intended. Systematic tests made with apparatus designed to 
