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merely pressed together into masses, which acquire a dark outward
appearance owing to superficial drying, and come on to the market
packed in casks as Negroheads, Sernamby, and, in the case of
certain kinds, as Cametas. According to the latest accounts,



Cametas in particular are derived from rubber-trees which have
become so badly scarred that it is no longer possible to extract the
latex in such a way that it can be smoked. The product obtained
in this way not only contains more water, but is a good deal more
impure than smoked Para, owing to its having coagulated on the tree.
In addition to particles of bark, sand is also an objectionable im-
purity in these unsmoked kinds of Hevea rubber. Still, when they

Fig. 5.

have been carefully cleansed, even these lower grades of rubber are
very useful.

A peculiar kind of Hevea rubber is " Mattogrosso Para" or
"Virgin Para" (not to be confused with the similar, but more
impure, "Virgin Sheets"). It is probable that this rubber is
derived from several species of Hevea; it is separated from the
latex by the addition of alum or other substances, and comes on
the market in large loaves with a pronounced cheese-like smell.
"Virgin Para" gives a very hght-coloured rubber when washed,
and vulcanises quite as readily as ordinary Para. Unfortunately


" Virgin Para " has, as a rule, the drawback of containing the hard
scales of beetles which have crawled into the rubber during the
coagulating process, and these cause endless difficulty in the
cleansing operations. Frequently they simply cannot be removed,
and the use of Virgin Para for certain purposes must for this
reason be, in general, excluded.

Fortunately, marked success has attended the efforts made to
grow the valuable Brazilian Hevea in plantations, and to cultivate
it instead of the unsuitable indigenous rubber-plants in Africa and
Asia. The plantations in Ceylon and the Malay Peninsula already
play some part in the actual production of rubber. On the planta-
tions, however, the rubber is not as a rule prepared from the latex
by smoking, but is separated by mechanical means. In order to
prevent premature coagulation of the rubber the vessels are partly
filled with water before use. The collected latex is filtered through
sieves, before undergoing further treatment, and is then allowed to
stand until the rubber-yielding substance has separated as a cream
on the surface. The cream is freed from the greater part of its
occluded water by a gradually increasing pressure, and is then
rolled or pressed into thin sheets, which are converted by slow,
carefully controlled drying into the wonderfully pure product which
is now known and valued under the name of "Ceylon Para." It
has now, however, become the general practice to wash and dry
the product on the plantations, by methods similar to those in use
in rubber-goods factories. However, the last word on the prepara-
tion of rubber on the plantations has not yet been said. In com-
paring the plantation Para produced sa far, with South American
Para, it must, of course, not be forgotten that there are no 150-year
old Heveas to deal with as yet on the plantations, as there are in the
Amazon district. The speed of vulcanisation of plantation Para is
the same as that of ordinary Para.

The Brazilian province of Ceara also produces, from its dry
stony soil, a rubber-tree — the Manihot Glaziovii — belonging, like
the Heveas, to the Eitj^horbia family. Rubber is obtained from
the Manihot by making an incision in the bark, and allowing the
latex to flow out and to coagulate without attention, partly on the
tree itself, and partly on the ground. When the rubber is scraped
up together, it is unavoidable that it should be badly contaminated
with fragments of bark and particles of sand. Despite the presence
of these impurities, Ceara rubber, which is also called in the trade
Manitoba (pr. Manissdba), after the Portuguese name for the
Manihot, is a good, strong rubber, very useful for many purposes.


Its resin-content is very little higher than that of Para, and its
speed of vulcanisation is very nearly as great. The inorganic
constituents are relatively high in Ceara, the high percentage of
magnesia being, apparently, characteristic of this kind of rubber.

The rubber from Hancornia speciosa, also a Brazilian product,
is of very much lower value than Hevea and Manihot rubbers.
The Hancornia grows in the provinces of S. Paulo, Bahia, Per-
nambuco, and Maranhao. Coagulation is effected by adding alum
or sea-salt to the latex, or even by merely allowing it to stand until
the rubber-cream separates. The cream is lightly squeezed and
dried, but still retains a considerable quantity of water. In the
trade the rubber obtained from the Hancornia bears the general
name of " Mangabeira," but latterly one has come across more pre-
cise names such as Santos Sheets, Rio Sheets, Pernambuco-Manga-
beira, etc. This Hancornia rubber is generally of a pale pink
colour, and has a strong smell of Moselle wine. One particular
sort only, Mattogrosso-Mangabeira, which has been on the market
for some time, is almost white in colour, with the same wine-like
smell. Mangabeira rubber contains about 6 to 12 per cent, of
resins, and differs from Para and Ceara in exhibiting a marked
sluggishness in vulcanisation, which necessitates the employment
of higher proportions of sulphur and higher vulcanising tem-

Formerly opinions differed very widely as to the tree from
which the so-called " Caucho " or " Peruvian ball " of commerce
is derived. On the one hand, it was assumed that Caucho was
yielded by Hevea, Cameraria latifolia and Hancornia speciosa.,^
whilst Henri ques ^ brought forward grounds on which he himself
doubted whether either Hancornia or Castilloa, which had
been mentioned by others as a source of Caucho, occurred on the
eastern slopes of the Andes at all. The present position is that
Dr. Ule's recent journey of investigation has shown that on the one
hand Hancornia speciosa does actually occur on the eastern slopes
of the Andes, and is much more widely distributed than had been
hitherto supposed, but that, on the other hand, Caucho is derived
from a species of Castilloa, viz., Castilloa Ulei- Warburg.^ This
fact explains the great similarity between " Peruvian " and " Ecuador
balls " and " slabs," of which latter the source was long ago shown

^ See Franz Clouth, Rubber, Gutta-percha, and Balata, Leipzig, 1899, p. 78.
Translation, London, 1903, p. 90.

3 Der Kautschuk und seine Quellen. Dresden, 1899, p. 13.
^ Gummi-Zeitung, 1905, xix. p. 962.


to be a species of Castilloa. The similarity spoken of is not limited
to external characteristics, but extends to the chemical composition
and the speed of vulcanisation of the rubber. The only surprising
thing is that, according to statements which formerly were frequently
made, the Caucho-Castilloa cannot stand even careful tapping, but
is completely destroyed by it, this being proffered as an excuse for
felling the Caucho trees, a usual practice in Peru and Western
Brazil, whereas Castilloa elastica stands tapping very well, and is
tapped in plantation -fashion over a considerable area in South and
Central America. The latex of the Caucho tree is mixed with the
sap of the Sachacamote, or with soapy water; the clots which
separate are partly freed from water and pressed together, the balls
so obtained being bound round with strips of raw rubber, thus
giving to the Caucho of commerce its characteristic outward appear-
ance. It is asserted that cutting down the Caucho trees would not
necessarily lead to their extermination, since the stump would very
rapidly throw up shoots, develop new branches, and in a few years
in the place of one felled tree a group of trees would be found.^
In spite of its abominable smell and the dirt which it contains, and
from which it is not easily freed, Caucho is a very valuable rubber.
Its resin-content is low, its speed of vulcanisation only slightly less
than that of Para sorts. In contradistinction to the latter and to
Ceara, Caucho is very dark in colour, after normal vulcanisation to
the stage of soft vulcanised rubber.

Castilloa elastica, mentioned above, with its numerous varieties,
is found growing wild in all parts of Central America, and as far
south as Peru in South America, and is already being extensively
cultivated. When carefully prepared the rubber obtained from
Castilloa is of quite a superior quality, containing little resin, light
in colour, not unpleasant in smell, and having a high speed of
vulcanisation. Unfortunately the methods of dealing with Castilloa
latex are generally still so crude and uncleanly that the rubber
produced for the most part lacks the good qualities which originally
belonged to it. The amount of Castilloa rubber which comes on to
the market, under the names West Indian, Ecuador, Gua^^aquil,
Centrals, etc., is very considerable. It is to be hoped that the
example of the planters in Southern Asia, who have obtained such
excellent results, both as regards the quality of their rubber and
financially, may serve as an incentive, and that we shall shortly
have upon the market notable quantities of fine Castilloa plantation

^ Clouth, Gummi, Gutta-percha, und Balata, 1899, p. 39. Trans., p. 56.


Within the last two or three years America has put on the
market yet another kind of rubber known as Guayule. The North
Mexican tableland produces a shrub — Partheniuni argentatum, A.
Gray, also known scientifically as Synantherea mexicana — in large
quantities. The bark of the shrub contains no latex, but the cell-
sap appears to contain the rubber-producing substance in suspen-
sion. The rubber is obtained from the plant in the following
way : — The plants are dried, milled and pounded, then macerated
with hot water, with or without the addition of caustic soda, the
cream of rubber which floats to the surface being then sieved in
order to remove as much as possible of the fragments of plant
tissue. The sieved product is partly freed from water by pressure,
made into the form of loaves, and packed in sacks. Guayule
cannot, indeed, be completely purified, but forms at the moment, on
account of its low price, a much-desired material, although its resin-
content is very considerable and its pungent, aromatic smell cannot
be destroyed.^

Whilst the greater part of American rubber is obtained from
large trees, Guayule forming an exception, in Africa the vines of
the genus Landolphia are at present the principal rubber-producers.
Besides the numerous vine species, however, certain trees, in par-
ticular the species of Kickxia (Funtuinia), play some part in rubber
production; further, the rhizomes (undergound stems) of certain small
shrubs, amongst them Landolphia Henriquesiana, Heim (formerly
called Clitandra Heiiriquesiana, K. Schumann), yield the so-called
herb- or root-rubber. Rubber-collection in Africa is still in a very
primitive condition. In spite of all regulations and prohibitions,
robbery of the trees, resvilting in their destruction, is still largely
practised. The methods of coagulation are still very varied.
The latex is either allowed to stand, with or without previous
dilution, until the rubber separates ; or, to effect a rapid separation
of the rubber, acid plant juices — for example, the juice of wild
citrons, or Bossassanga-juice — are added ; or the latex is sprinkled as
it flows from the incision with an acid plant extract or with salt
water, thus enabling the collector to draw away the rubber in the
form of a thread or ribbon, which can then be wound up into a
ball; or the negro smears the latex over his body, where it is
allowed to dry, and is then rolled up into the form of balls or
strips. Sometimes typical pieces of rubber are found in one and
the same parcel, which clearly show that the individual native

' With reference to the future supply of Guayule rubber, see Board of Trade
Journal lltb June 1908.


collectors have employed quite distinct methods of collection. The
quality of African rubbers varies very much even amongst parcels
of the same origin. A cursory examination of the announcements
of auctions published by the registered Antwerp brokers, which in
every case give a correct idea of the condition of the lots coming
under the hammer, is sufficient to show this. Unfortunately there
is to be found against so many brands of rubber otherwise known
as good, the warning : ''fort collant " (very tacky) ; "fort charge de
matiere etrangere, de sable " ; " en ferraentation," etc. (containing a
laFge amount of foreign matter, or sand ; fermented, etc.).

Generally speaking, African rubbers vulcanise a good deal more
slowly than Para and Ceara, and require more sulphur — particularly
the more resinous sorts — and higher vulcanising temperatures.
The smell of the drier sorts of African rubber is, as a rule, quite
tolerable, sometimes even pleasant ; but the softer sorts generally
possess a most unpleasant smell. The drier sorts usually give a
much lighter-coloured sheet, after washing and drying in the
factory, than do the softer kinds. There are only a few sorts of
African rubber which are constantly of a very good quality, and
amongst these should be named in particular the so-called " Massai
niggers " of French Guinea and Sierra Leone, the " red " and
" black " Kassai of the Congo, Equateur, Upper and Lower Congos,
Lopori, etc. ; and in the case of East African sorts, Mozambique
"balls" and "spindles." In the case of Lopori, Equateur, and
similar sorts of Congo rubber, considerable variations in quality no
doubt occur, but the quality which is designated " Prime " from
these sources is always pretty constant ; at any rate the slight
variations that do occur are of practically no importance in the case
of goods vulcanised by heat. The medium and lower sorts of African
have a very high resin-content. It may be mentioned that certain
sorts of Madagascar rubber have the reputation of being particu-
larly suitable for ebortite manufacture. In the Gold Coast colony,
in West Africa, Hevea hrasiliensis is also cultivated. In several
of the African colonies Government regulations have been framed
prescribing the planting of a certain number of rubber trees for
every given quantity of rubber collected. If these regulations
were strictly conformed to, the wholesale destruction in the African
rubber districts, which was at one time feared, would be prevented.
Such a long period must, however, elapse between the planting of the
tree and the first tapping, that competent authorities fear that the
total rubber output of Africa will drop during the next few years.
Finally, rubber cultivation has been taken up in the Cameroons,


and amongst others the " Kamerun-Kautschuk Compagnie A.-G."
has been registered in Berlin with a capital of three million marks.

In Asia rubber is obtained from a number of different trees, the
latex from which is worked up together, as in the case of the vines.
For this reason it is even more difficult than with African rubbers,
leaving out of consideration the finest qualities obtained from the
plantations, to determine the origin of commercial sorts of Asiatic
rubbers. Amongst wild Asiatic rubber-plants Ficus elastica holds
a premier position, but Willoughbeia firina smd fiavescens, Urceola
esculenta, Leuconotis eugenifolius, Calotropis gigantea, and Cryp-
tostegia grandiflora also yield rubber. The solid rubber is obtained
either by skimming the latex and drying the cream so removed, or
by boiling the latex until the rubber separates from it ; to a great
extent, also, by the addition of a kind of gypsum or other
substances which have a chemical action on the latex, or by simply
allowing the latex to flow from the tree and dry upon the trunk or
on the ground. The value of the rubber obtained varies a great
deal. In some brands it is customary to distinguish between no
less than four different qualities. The rubbers obtained from
indigenous Asiatic plants are usually rich in resins, and, like
Africans, behave sluggishly on vulcanisation.

It has already been mentioned that Hevea is being successfully
cultivated and employed as a rubber producer in Ceylon and the
Malay Peninsula. Ficus elastica has also succeeded well in the
Dutch Sunda islands, and intelligent treatment of the latex has
already resulted in the production of a thoroughly well-prepared
rubber. This plantation rubber will also become, in the near
future, a permanent feature of the market, gradually increasing
in quantity, for at the beginning of the year 1906 a ''Borneo-
Kautschuk-Compagnie A.-G. " was formed in Berlin with German
capital, in order to cultivate rubber in plantations.

There is no doubt that plantation rubber has a brilliant future
before it. By the skimming process, which is almost universally
employed on plantations, rubbers are obtained, not only in the case
of Hevea latices, but also from Castilloa and Ficus, which leave
practically nothing to be desired, and which have the distinguishing
characteristic that they contain no dirt, and as a rule no appreciable
quantity of proteins and putrefactive bodies, the natural resins of
the particular latex being practical^ the only impurities present.
Their permanently pale colour is also one of the decided advantages
attending their use.

Latices do not contain solid rubber as such, but a substance


which is cpable of being transformed into rubber partly hy
mechanical and partly by chemical agencies. By extracting a latex
with ether, and carefully evaporating the ether from the extract,
the rubber-yielding substance is left behind as a thick oil, which is
transformed into solid rubber when rubbed with a glass rod or
treated with a little acid. The change which takes place during
this solidification is at present regarded as a process of poly-

The " rubber-substance " proper is an unsaturated hydrocarbon,
or possibly, to speak more correctly, a mixture of unsaturated
hydrocarbons. According to the investigations of C. Hariies,
caoutchouc appears to be a polymer of cyclo-dimethyloctadiene.
In addition to this "rubber-substance," rubber contains varying
proportions of resins, from w^hich it may be freed without difiiculty
by extraction wdth hot acetone in a Soxhlet or similar apparatus,
provided that only thin, washed and dried sheeted rubber be used
for the extraction. If after this extraction with acetone the
residue be further extracted with carbon bisulphide, chloroform, or
some other solvent of rubber, the " rubber-substance " dissolves and
goes into the extract, and there remains a residue consisting partly
of organic, partly of inorganic substances. This residue frequently
contains appreciable quantities of nitrogen-containing substance,
which is designated, in general terms, mucilage or protein substance.
If care has been taken, in coagulating the rubber, to keep it as free
as possible from albuminoids — as in the instance of Ceylon Para
— traces, at most, of nitrogenous matter are found in the residue,
which does not, when incinerated, give off the characteristic smell
of burning hair or horn. If, however, coagulation has been carried
out in such a way as to retain practically the whole of the albumi-
noids of the latex in the rubber, the insoluble residue gives a very
marked smell of burning hair or horn when incinerated. The
inorganic substances mentioned as being present in the insoluble
residue, or in the ash, may consist partly of such impurities as
were not removed by the washing process, but are also partly
derived from organic salts contained in the rubber.^ Para rubber
generally contains (chiefly) calcium salts, while African rubbers
contain ferrous salts, and Ceara magnesium salts.

Generally speaking, it is desirable that a rubber should contain

only a low percentage of resin, and as little albuminoid and other

organic impurity as possible. A small amount of albuminoid

matter, provided it is in good condition and free from bad

* Henriques, Der Kautschuk und seine Quellen. Dresden, 1899, p. 25.


smell, as, for example, in the case of Para, is, of course, quite
harmless. Further, the rule may be laid down that the commercial
value of a rubber as well as its physical properties — especially
after vulcanisation — are roughly proportional to the percentage of
rubber hydrocarbons present in it. This, as is .well known, is like-
wise true for different kinds of guttapercha. This statement is, of
course, only strictly true for cases where the rubber hydrocarbons
do not differ from one another very much in their degree of poly-
merisation. Valuation on the results of chemical analysis does not,
however, do away with the necessity of making certain physical
and manufacturing tests. One is unable to decide from the results
of a chemical examination whether a particular rubber will be
certain to yield on vulcanisation a floating product such as wilT
bear some weighting with pigment, or whether the ebonite prepared
from a given rubber will take a good polish or not. Every branch
of the rubber industry makes special demands on the rubber to be
used in it, and suitable tests must be adapted to these special
demands. To this circumstance must be attributed the fact that
while one manufacturer swears by a particular brand of rubber,
another finds it to be of quite inferior merit, simply because it is
quite unsuitable for his particular purposes. In many instances
when judging of the usefulness of a rubber, another factor comes
in, to which just as much importance has to be attached as to the
results of chemical analysis or of practical tests, the question,
namely, as to whether the rubber under consideration is always to
be had in sufficient quantity. Large factories produce certain
goods on such a colossal scale that they cannot risk basing all
their calculations upon the use of certain rubbers, if the sorts in
question cannot be purchased without difficulty at any time and in
sufficiently large quantity. For this reason the smaller factories
stand in the advantageous position of being able to cover a con-
siderable portion of their requirements in crude rubber by
opportune purchases of small parcels. When these facts are taken
into consideration, it is easy to understand why certain sorts — for
example, " Massai niggers " — upon which large factories can rely are
regularly purchased at prices which do not actually represent their
true value, while small lots of the finest Congo sorts can be had
comparatively cheap.

In addition to true rubbers, " pseudo "-rubbers are used in the
rubber industry to quite a large extent. Tliese " pseudo "-rubbers
consist essentially of i-esins containing a small percentage of a
rubber hydrocarbon, and come on to the market as " Paste " or



"Flake." Of late these pastes have been commg not only from
Liberia, the Gold Coast, Gaboon, and the neighbouring countries,
but also from Central America, under the name of " Mono Rubber."
Besk or Pontianac, also called Gutta Jelutong or Dead Borneo,
is interesting from the fact that the resins, of which it chiefly
consists, behave exactly like the resins of true guttapercha and
are probably closely allied to them.

The following table gives some analytical data for a number of
different kinds of raw rubber. The very complete raw rubber
tables of Drs. Henriques and Soskin, given in Herbst's Guomni-
kalendar'^ from year to year, may be referred to in this connec-
tion. These tables give not only accurate information as to the
geographical origin, trade-name, export towns and botanical origin
of every single commercial sort, but also include important notes
as to their appearance and properties, average price, mean loss on
washing, and resin-content.

In the Washed and Dried Rubber

^kTrtv^-iri /^f T? Til-\l-»y-it.

JName 01 rtuDDer.


per cent.



Pure rubber.

per cent.

per cent.

per cent.

per cent.

Para, fine .






,, entrefine






Ceara .






Columbian .






West Indian








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Online LibraryAdolf HeilThe manufacture of rubber goods : a practical handbook for the use of manufacturers, chemists, and others → online text (page 2 of 21)