CAOUTCHOUC AND GUTTA-PERCHA. 215 
Caoutchouc and gutta-percha can be easily distinguished from each other. 
First, they are entirely different in their structure. When gutta-percha is 
rolled into thin sheets, or drawn into strips, it is like a fibrous substance, which 
is not the case with caoutchouc. A thin strip of gutta-percha can be con- 
siderably stretched in one direction, in that of the fibre, but it tears at every 
attempt to stretch it obliquely to that line, while caoutchoue is easily stretched 
in every direction. When thin sheets of both substances are examined in 
their relation to light by means of polarization caoutchouc shows little, if any, 
change of color, while gutta-percha offers fine appearances. The latter seems 
to be constructed of prisms of the most variegated color, which appear to be in- 
terlaced in each other, 
In a chemical way, too, the two substances can be distinguished from each 
other by means of chloroform. Gutta-percha is dissolved in it boiling ; it yields 
no ether from the solution by distillation, but an alcohol in the form of a white, 
ductile, not sticky membrane, and such is its residue after the evaporation of 
the solvent. Caoutchouc, on the other hand, swells up in boiling chloro- 
form, and only when the jelly has been divided by chemical means, perfect so- 
lution ensues in the further process of boiling. Alcohol acts here as a means of 
distillation; the caoutchouc is secreted as a coherent, not as a sticky mass. 
In this way the two substances can be detected even when mixed together. 
Of the formation of these two vegetable substances we know nothing, and 
neither do we know more of the part they act in the organism of plants. In 
order to avoid the difficulty, they are designated as secreted matter. 
When Montgomery sent to London the first specimens of gutta-percha he 
chiefly recommended it for the purpose of manufacturing surgical instruments, 
as those made of caoutchouc would soon become softened and glutinous. It 
was, however, soon found out that the excellent qualities of gutta-percha render 
it, much more than caoutchouc, appropriate for a thousand other uses; it espe- 
cially promised to become a substitute for leather, showing none of the disad- 
vantages presenting themselves at the application of caoutchouc for the same 
purpose. Besides, it is not subject to wear and tear; and when the shape into 
which this pliable mass is cast gets out of fashion, it has only to be put into 
hot water in order to be transformed, or used for something quite different. 
Although known only for a short period of time, it is already used for the manu- 
facture of so many things, and the ways of manufacturing it are so manifold, 
that it will be difficult to present here a true picture of the whole. 
The operations used in working these two substances are common, in part. 
The first is that of cleansing them from foreign admixtures, the black Java 
caoutchoue, particularly, containing a considerable multitude of small stones 
and vegetable particles. At the purchase of caoutchouc the quantity of water 
it contains is, above all, to be taken into account, that admitting of deceitful 
augmentations. Tor not only is thereby the real value diminished by a fourth, 
but it also loses considerably of its toughness and ductility, while its whiter 
color apparently indicates a better sort. 
The cleaning operation is executed partly in a mechanical and partly in a 
chemical way. ‘The mass passes between two turning cylinders, corrugated, 
overlying each other horizonally; this removes the stones and similar sub- 
stances. In order to make this process complete the rolled sheets are washed 
in lye. A large number of these leaves are pressed together in a heated 
cylinder, which gives them great uniformity. When in large plates caoutchouc 
is put under a hydraulic press, where it is subjected for six or eight days to a 
severe pressure, at a temperature of from 45° to 50°. When very thin sheets 
are to be obtained, the heated mass passes through a rolling machinery, the 
hollow cylinders of which are heated to a temperature of 100°, by means of 
steam or of hot iron bars, and which are gradually placed tighter and tighter. 
The mass being very adhesive in heat, sheets of every length can be obtained 
