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increase may be explained by considering that when a beam is bent to the elastic 
limit of the outside fibres, connection between these fibres and those just below 
will prevent the free contraction or expansion of the outside fibres, and thus the 
beam has its elastic strength increased. In case of harder steels and materials 
such as cast iron or wood, no such increase may be expected. Experiments are 
being carried on by the writer to determine as completely as possible the increase 
of the elastic limit as a function of the shape of the cross section. Up to the 
present a series of | beams have been tested, and a series of flat plates. The tests 
in flexure are compared with tests in tension on material cut from the flexure 
specimens. The plates were partly 63” <1’ with span of 28” and partly 
73’ « 13” in section with a span of 40’. The increase in the elastic limit for 
the plates was 55 per cent. in the first case and 27 per cent. in the second case. 
A specimen 3” 4” in section tested with a span of 57’ showed an elasti 
limit of 42,000 lbs. [/’”. A tension test was not made of this material, but the 
44 
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yield point reported by the mill is 37,950 lbs. [_} Mr. Gus Henning has shown 
that the elastic limit of rolled material is some 4,000 lbs. "| less than the yield 
point from the billet, and if the 37,950 Ibs. [| is thus reduced, the 42,000-lbs. 
()” elastic limit in flexure will represent an increase of 27 per cent. 
When the height increases in comparison with the breadth, the excess 
strength in flexure disappears, and for the 7 beams tested the elastic limit in 
flexure was slightly less than that of a tension specimen cut from the web. 
It is to be noticed also that, in the case of flat plates, there is not free elastic 
expansion in the side direction during flexure; consequently the modulus of 
elasticity should be increased. The tests on seven plates show an average in- 
crease of 3.6 per cent. in Young’s Modulus. 
NorE ON COMPRESSIVE STRENGTH OF WrouGHT IRon. By W. K. Harr. 
While the tensile strength of wrought iron or steel is a definite quantity, the 
compressive strength is not so well defined. In the case of wrought iron the 
compressive strength is quoted by different authors in values from 40,000 to 90,000 
pounds per square inch for a state of stress consisting of compression in one direc- 
tion only. The strength of any specimen is a function not only of its physical 
properties but of its shape, and the maximum resistance to compression may be 
anywhere from the elastic limit to the plastic limit, depending on the shape of 
the specimen tested. It is not customary to test iron and steel in compression, 
since the results of a tension test give an index of the capacity of the material to 
