CAOUTCHOUC AND GUTTA-PERCHA. 211 
touch each other he presses them carefully together, and the tube is done. The 
value of those tubes is enhanced by other chemical properties of the substance, 
which is insensible to the influences of many acrid liquids and vapors. Chlorine 
gas, hydrochloric, and many other acids and caustic alkalies, do not affect it. 
Concentrated sulphuric acid causes a carbonization of its surface, but a further 
decomposition only at high temperature, sulphurous acid being evolved, and 
the gum assuming the softness of resin. Nitric acid makes it yellow, and, after 
some time, soft. In the fuming acid it dissolves, evolving carbonic oxyd. But 
a mixture of concentrated sulphuric acid and nitric acid acts most destructively. 
The comfnon solvents exercise no influence on caoutchouc. The solution of 
this substance was, therefore, a long time an enigma to chemists, even after Mac- 
quer’s pretended discovery in 1768 of the key to it. It was Pelletier who first 
indicated the right way of doing it. Having been softened in hot water, 
caoutchouc is solved by ether freed from spirit of wine. Without this precaution 
the substance is only softened, as it is by petroleum or spirits of turpentine. 
At the same time the substance increases by swelling even to thirty times its 
volume. It is an easy matter to blow the softened flasks into a considerable 
size. Mitchell expanded a caoutchouc bladder of the size of a walnut to fifteen 
inches diameter. He prepared such balloons, some measuring six feet in 
diameter, whith, being filled with hydrogen gas, serve as toy balloons for 
children. One of these balloons having slipped from his hand, came down to 
the ground only at a distance from the town of a hundred and thirty miles. But 
caoutchouc swelled in rock or turpentine oil can be so much extended by the 
application of heat and mechanical means, larger quantities of the liquid being 
radua.ly added, as to appear dissolved. 'The caoutchouc membrane, however, 
which is left after the evaporation of the solvent, has the inconvenient property of 
long remaining sticky. To remedy this inconvenience, Benzinger has by acci- 
dent discovered an efficient means, not yet widely known, in the admixture of a 
very small quantity of a concentrated solution of sulphuret of potassa. 
Better solvents for caoutchouc have lately been discovered. Such are 
chloroform, sulphide of carbon, and chiefly those earburetted fluids which are 
derived from the distillation of tar or of caoutchouc itself. In one factory at 
Greenwich, England, about eight hundred pounds of waste caoutchoue are daily 
subjected to dry distillation in iron vessels. When this operation is not carried 
too far there remains a greasy mass, which retains this property, and effectually 
withstands the influence of the air and water. For this reason it is used in 
England for the purpose of saturating cables, and thus rendering them more 
durable. A similar greasy mass is gained by melting caoutchouc at a tempera- 
ture of 125°. It swells and burns with a bright whitish flame, so that in 
South America caoutchouc is used for purposes of illumination instead of candles 
and torches. 
In the mineral kingdom, too, substances are found which in their external 
properties greatly resemble caoutchouc, but resist the power of solvents still 
more effectually than the vegetable material. A, similar substance can be pro- 
duced artificially by exposing thin layers of linseed oil to the air for six or 
seven months. 
As early as a quarter of a century ago caoutchouc had become a branch of 
industry of some importance. But the English imports of the raw material 
show that it was still resting on an uncertain basis. While in 1829 about 
100,000 pounds of elastic gum was imported, its consumption in the following 
year reached only half that amount. In 1833 a duty was paid upon no less 
than 178,675 pounds. The properties of the raw material itself greatly restricted 
its manufacture. The use of the articles manufactured was changeable and 
limited. By moisture and cold gum-elastic partly loses its elasticity, and be- 
comes hard, but it is softened by heat and compression in the hand. Many an 
article that was very useful in summer had to be put aside in winter. The 
