The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1880-11-27

than unaltered caoutchouc; aud il is quite
possible to obtain photographic print by
exposing q film Of India,rubber under a
negative, and then dissolving away those
parts on which the light has not acted by
means Of benzole. II is generally q dis
Greet thing to keep India-rubber where il
will not be exposed to the prolonged action
Of powerful light, although there are
cases in which exposure to light is use
full aid TO the process of vulcanization.
lndia-rubber is, to certain extent, porous
and cellular in its texture, as may be seen
by a microscopical examination Of a thin
section. Again, il thin leaf Of caout.
chouc is boiled for a long time in water il
absOrbs a considerable proportion of this
liquid. The amount may, in some cases,
rise as high as 25 per cent In similar
manner alcohol is absorbed by India-ru
Der, but this fluid Is absorbed more readily
than is the case with water.
Now We pass on to a moro important
matter, namely, the action Of such liquids
as benzole or coal naptha on caoutehouc
Here are two cubes OF Para rubber, each
being three .eighths Of nm inch across the
face. One Of these I will preserve as
pattern, and the other viii suspend in
a bottle containing benzole. The cube
suspended in the bo1Iole will imn ediatey
begin to swell, and will continue to do so
until it has attained bulk about one hun
dred times as large es its original size.
During the time that the cube is swelling
in the benzole a certain proportion of the
caOutchouc will become dissolved out, and
incorporate itself with tho bulk Of the SOL
vent. Now, as a matter Of fact, every
kind Of natural India.rubber contains two
distinct notifications Of caoutchouc, one
ofwhich tends to swell up in such liquid
as benzole, while tic other dissolves and
forms true solution. The first mentioned
Of these bodies may be referred to as the
fibrous constituent of caoutchouc, while
the second may be spoken of as the viscous
constituent The proportions in which
these two bodies occur 10 raw rubber va.
ries extremely; Para rubber, Of good
quality, containing only small proportion
Of the viscous constituent, while African
tongue, on the other hand, consists prin.
cipally Of the viseous modification Of caout.
chouc. The viscous constituent Of caout.
choac is the agent principally concerned
in the joining together Of freshly cut edges
Of lndia-rubber. The treatment of the
juice Of the Iudia-rubber trees is often Of
such nature as to greatly deteriorate the
caoutchouc obtained q considerable pro-
portion being thus changed from the fibrous
to the viscous condition. This kind of in.
jury to the caoutchouc can be obviated by
coagulating the milky juice, and carefully
drying the clot after it has been subjected
to pressure. For experimental purposes
alcohol may be employed as a coagulating
agent; while, on an Industrious scale,
alum has been tried with apparently an
excellent result The milk is strained to
remove solid impurities, after which a
small proportion of alum solution is added.
The clot which separates Is next drained
or pressed, after which il is dried. Caout-
chouc dissolves more or less perfectly, nc
cording to its condition, in various liquids,
among which may be mentioned the various
fixed aud hydrocarbon oils, chloroform,
ether, and carbon disulphide. Unless how
ever, the caoutchouc has been masticated
or otherwise degenerated, it is doubtful
whether a true solution is obtained. When
clear limpid solution is required, one oil
the best solvents is that proposed by Payen,
namely, carbon disulphide, mixed with
per cent. Of absolute alcohol. If one part
of masticated caoutchouc is dissolved iu
thirty parts Of the above solvents solu.
tion is obtained which can be filtered
through paper, and may be employed in
covering the most delicate moulds with
successive myers of caoutchouc.
Caoutchouc may be utterly ruined by
the use Of impure solvents, and those ex.
perimenting with 1ndia-rubber solutions
should in cases where il is desirable to re.
generate the caoutchouc, by allowing the
solvent to eyaporate, take the utmost care
not to employ any solvents which contain
fatty or greasy matter.
Weak or diluted acids have little or nc
action on caoutchouc in the majority oil
cases, but strong sulphuric acid slowly
acts on il, the action becoming rapid i
heat be applied. Strong nitric acid acts
on it with some energy, causing its entire
destruction, and in similar manner it j.
destroyed by the prolonged action of chic.
rine, bromine, or iodine although these
reagents, when their action is kept under
control, have yulcauizing or strengthen,
ing action. lETT T-Ff / =