NOVEMBER 19, 1897.-] 
ofrupture. This can be readily felt in even 
the breaking of one of the small bands of 
partially vulcanized rubber now so univer- 
sally employed for filing papers and other 
purposes. At the end of the period of ex- 
tension the resistance rises so rapidly as to 
produce the sensation of bringing the hand 
up against a rigid obstacle, resisting further 
elongation. 
Figure 1 is the stress-strain diagram of a 
strip of rubber, partially vulcanized, but not 
sufficiently to disguise the peculiar charac- 
teristics of the material. 
Studying this diagram, it will be ob- 
Sar 
SCIENCE. 
759 
any indication of that method of flow of 
the mass which, in the case of the irons 
and softer steels, for example, permits a 
falling-off of resistance after passing a point 
of maximum tenacity well within the 
breaking limit. The ratio of increase of 
load to increase of elongation steadily in- 
creases from the zero point, as with all sub- 
stances, other than iron and steel, so far as 
known, up to this point of contrary flexure 
on the diagram; at which place the ratio is 
inverted and resistance increases in greater 
proportion than extension, finally assuming 
a comparatively high value. 
o:35 
Strain per Unit Length. 
Fie. 1.—Stress-Strain Diagram of India Rubber. 
‘ 
served that the substance behaves precisely 
like other familiar materials, up to a point 
which, in this case, is found at a load of 
thirty per cent. of the maximum, the break- 
ing load, and at an extension one half the 
maximum. At this point there exists a re- 
versal of the line, and the curvature is 
thence maintained convex to the axis of X, 
up to the point of rupture; fracture tak- 
ing place, at the end, sharply and without 
The singularity of this action will be 
brought into relief by examining the dia- 
grams produced with other materials em- 
ployed in the arts.* Swedish or Norway 
Iron, Common Merchant Iron, ‘ Mild’ Steel, 
and Tool-Steel have been subjected to 
loads increasing to the point of rupture, 
with occasional removal of the load. 
*Thurston’s Materials of Engineering, Vol. II., p. 
611, 
