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


of on tho unsuspeeting merchant as caout-
ehoue, are made into balls, and sold as
"negro head" The negro head rubber is
frequently made into crude representations
of animals, which win pass about equally
well for horse, pig, or a crocodile.
The milky juice Of tho Para rubber
trees has approximately the following com.
position:
Caoutchouc
Aibufnihous, cxtracttve, and saline matters..l2
"ater...'".'"""..",....
tf boz. rt ~ r.. 100
As rubber producing tree, the Fcus
etdsticd stands next 10 importance Of the
heyeas, The Flcw eiastica grows abun-
dantly in India aud the East Indian Is
lands, one district in Assam, thirty miles
long by eight miles wide, being said to
contain about $4,000 trees, many of them
attaining height of hundred feet. This
tree also grows freely in Madagascar, and
il is well known 10 US as greenhouse
pant.
The juice Of the Ficas elastica contains
notably less caoutchouc than that OF the
American trees, the proportion very often
falling as low as ten per cent. Of the juice.
a vine like plant, the Urceola eidstica,
which grows abundantly 10 Madagascar
Borneo, Singapore, Sumatra, Penang, and
other places, yields considerable amount
of caou,chouc of very good quality.
Africa yields a considerable quantity Of
caoutchouc, but generally soft and of infe
rior quality. 1t is believed to be yielded
by various species of lundolphia, fcus, and
toxicophea.
Caoutchouc is nearly colorless, and when
10 thin leaves tolerably transparent. 1t,
like very many other substan noes, contains
nothing but carbon and hydrogen, but its
properties differ very widely from those Of
other hydrocarbons almost identical ia
composition. 1t has been found to con-
tain, in one hundred parts, 1875 of hydro
| gen aud S7'5 Of carbon.
Caoutchouc, asmight be supposed, burns
very readily, aud leaves no residue. 1t is
soft, aud very imperfectly elastic, 10 the
true sense Of the term that is to say, il
does not return to its original dimensions
after having been considerably stretched
As regards the stretching Of Indiarub-
Der, there is point at which il requires n
greatly increased force to stretch Il and At
this point il seems to become fbrous in
texture, as you may perceive by examin.
ing this extended sample by the aid of a
magnifying lens. India rubber has valua.
bic electrical properties, as Won are no
doubt aware, il being an admirable insu.
lator, aud having a remarkable tendency
to become electrical by friction.
Freshly cut surfaces of India.rubber
cohere very strongly when brought into
contact, and this is well illustrated bv tho
old way Of making a tube of unyulcanized
caoutchouc.
Cold has remarkable effect on caout.
chouc, rendering it rigid aud ipelastic and
this circumstance considerably detrac,s
from the value of unyulcanized Indin.rub.
Der. A strip of India.rubber soft and
pliable, will, upon exposure for a few
minutes to temperature Of % Cent. OF
the freezing point, become rigid and stiff
but its original pliatilty may be restored
either by warming or by applying suficien,
tensile strain to it, to extend il to three n,
four times its length. In each case il i.
restored to its original condition. In tho
case Of the stretching it is very likely tha,
the effect is due to heat evolved durino
the operation.
The effects Of heat on India rubber pre.
sent many points of interest. A band Of
caoutchouc attached one end to an iuder
stretched to the zero of a paper scale will
If gentle heat be applied to il eon,roct
as regards length, but EXPANDS in a trims.
verse direction, causing the index TO move
rapidly thrUugha space of several degrees
This property, which stretched caoutcboue
possesses, Of contracting by heat. NAV he
described BY saying that within certain
limits the tensile elasticity of eaoutcbonc
is increased by an elevation Of temnoro.
ture. Caoutchouc, however, If heated "a
1909 Cent, softens considerably. and al
most entirely loses its elasticity. while .
heat Of l206 Cent produces a mos, 5eo;,
ded softenipp effect ON eaou,cbou, of ,ho
best quality, but after expospre 10 iii,
temperature il RECEIVERS its nr;s,;no s,a,,
by exposure to cold for n moderate nsr;od
II, however, lhe action of heat has hasr
pushed still further, saw to 9ooo Csn,
the caou,chouc becomes converted into !
permanently viscous BODY. which has lit,lo
or no tendency to harden ngain Th;.
viscous substance possesses tho sams eo,r
position as unaltered caoutebouc and i .,
value as medium for makinc air,,;ab,
joints, which can be easily undoue
When eaoutchouc is subjected ton Tom.
peraturc somewhat above 2OOo Cent !,
becomes converted into n variety of vola
tile hydrocarbons. which nresent monv
points of interest, aud YOU win 6od n toi.
erably full account Of them il The man
uals Of chemistry India. rubber il ssubise,
to two kinds of deterioration and decav
In one instance It tends to become so4
and loses its elasticity. while in Tho other
it becomes friable, ycllowish. and resino6.
in its nature. The last ment;onod Iin5
I