The Washington herald., 1921-09-18
CHEAP @nIRERAL RUBBER
MADE OF ASPHALT.

ChEhf lhEhAb hDbbEh
MADE OF ASPHALT.
New uses for a substance czIeo
mineral rubber. although IL con-
tains no rubber. were detailed by
C. o. North. OF Akron. Ohio, At the
recent meeting Of the division Of
rubber chemistry OF the American
Chemical Society At New York.
Mineral rubber, or NIB as IL IL
more commonly known. gets its
name from the fact that Il was for
merly prepared by blending natural
asphalt with a harder bitumen such
as gilsenite. Today IL is largely
manufactured by heating to a high
temperature while blowing with
air. a mixture OF gilsenfte and stfU
residue from the distillation OF
Mexican or Oklahoma petroleums.
he said.
1T is not a rubber. which is
strictly a vegetable product. How
ever. it has sor1e OF its properties.
Before heating with sulfur under
pressure, l. e., before IL is vulcan
lied, rubber is plastic. When
strained il flows like coal tar or
other amorpheus solid. Similarly.
its viscosity is materially altered by
temperature change. When vulcan
lied il becomes elastic: that is IL
now has the property Of recovering
its original length when released
from strain. Unyulcanized rubber fy
largely plastic with little elasticity.
Eulcanized rubber is chiefly elastic
and but slightly plastic. Minerar
rubber is plastic both before and
after Inflammation
Mineral rubber is not q rubber
substitute nor an aduIterant Of rub
ber goods. II is strictly an aid ur
compromising ingredient II Is ono
Of the cheapest, costing but to
cents per pound. il is usually pres
ent in tires and other rubber ar
ticles. When properly used il m
creases the life and service Of tho
articles containing il. a common
example Of incorrect and excessive
use of MR is found in many cheap
overshoes. When purchased they
can hardly be put on. Due TO plss-
ticity introduced by the Mr. thev
soon acquire a decided stretch auI
can hardly be kept on ones shoes.
When a vulcanized compound
containing mineral rubber is
stretched the Mr. flows out with
the rubber and is pulled hack by DO
on release Consequently as mu-I
as 40 per cent Of Mr. by volur.
may be added TO rubber without
greatly affecting its tensile strength
or the limit TO which il may he
stretched II these were the only
factors MR. would be very eNIen-
sively employed.
Unfortunately il has no tough
ening properties. such as are i'm
parted by gas black or zinc oNidr.
When used in excess Of Is per cont
by volume il slows Up the recover,
of compounds containing it THIS
property is known as loECiness r-
laziness and Is due to th- slow Tru
Of MIR when pulled back by tls rub
ber on contra ction. This may Co.,
illustrated by a gum band cyrra. .--
ing more MIR than desirable When
released il comes back quickly ty
a certain point and then conrfnur~
to slowly contract for about
tventy-foUr hours. At this tim.
the length will Approximate that uf
a pure gum band within a lev
minutes after release
The time factor fntroducrs FE
excessive employment Of nfrc-a
rubber is very serious. czuSr--
tread separation in pneumatic rf--.
and other kindred troubles wh..
properly used its effect is parti~l-
larly beneficial.
The properties Of mineral r-uhto-
may be altered by using dTfo-,-.
materials and methods OF prepara
tion. IL an MR. can be prcpa-ra
without the excessive Elasticity ,.
the present material IL will b. ,rr-
ployed more extensively ana r
larger amounts than are puss.1-.
today, thus decreasing the COS, %.
rubber goods Of all kinds