CAO 
from burning fuel ; when dry, the clay mould 
is crushed, and the fragments extracted, and 
in this manner the spherical'" bottles are 
formed. It has since been discovered, that 
caoutchouc is not exclusively the produce 
of this vegetable ; but that it is famished 
likewise by other plants, either perfectly the 
same, or with very slight variations of pro- 
perties. It is obtained in large quantity 
from the Jatropha elastica, a native likewise 
of different provinces of South America. 
Fourcroy procured specimens of the juice 
of the caoutchouc in the state in which it 
exists previous to its inspissation, from the 
island of Bourbon, from Cayenne, and the 
Brazils, and examined its properties. From 
experiments he concluded, that caoutchouc 
exists ready fanned in the juice of the tree, 
and is capable of being separated in the 
concrete form ; but that a portion also ex- 
ists not sufficiently perfect to be deposited 
with its elastic property ; that it acquires 
this, together with its inspissation, from the 
action of oxygen ; and that by this opera- 
tion, exposure to the atmosphere influences 
the concretion of caoutchouc in the usual pro- 
cess in which it is brought to the solid form. 
The purest caoutchouc Fourcroy sup- 
poses to be that which separates sponta- 
neousiy from the juice in close vessels. It 
is white, or of a slight fawn colour. The 
properties of caoutchouc have been deter- 
mined principally from the state in which 
it exists in the elastic bottles which are im- 
ported to Europe ; and in this state its pro- 
perties do not seem to have undergone any 
important change, or to be diflferent from 
those of the pure caoutchouc. Its colour is 
a dark brown ; its external surface is smooth ; 
its internal texture, is rough, and presents a 
fibrous appearance. Its specific gravity is 
nearly the same with water, being from 
9.3 to 10.0. It is inodorous, and is also 
destitute of taste. 
The most remarkable physical property 
of which this substance is possessed, and 
which eminently distinguishes it, is its high 
elasticity. It can be stretched out to a 
great length, and when the force that has 
been applied to it is withdrawn, it instantly 
returns to its former dimensions. Its pliancy 
is increased by heat, while it is rendered 
more rigid by cold ; and its softness, which 
is connected with the former quality, is so 
much increased by warmth, that it can be 
moulded into any form, and two parts newly 
cut may even be pressed together, so as 
to be intimately united. 
Caoutchouc, exposed in a dry state to a 
CAP 
high temperature, softens, swells up, and 
emits a fetid odour similar to that of animal 
substances: as the heat is increased, it melts 
into a viscid matter, and remains in this 
state when cold. If heated sufficiently high 
it takes fire, and burns with a vivid light 
and dense smoke ; in the countries in which 
it is produced it has been used for torches. 
It is perfectly insoluble in water and alco- 
hol, but is dissolved in ether. 
This substance is capable of being applied 
to important purposes, from its softness and 
flexibility, its elasticity, and particularly its 
indestructibility, and not being affTected by 
air, water, or indeed the greater number of 
chemical agents. Tubes for conveying gases, 
and other chemical instruments, are accord- 
ingly prepared from it ; and bougies, cathe- 
ters, and similar surgical instruments of 
caoutchouc, are much preferable to what 
can be prepared from any other substance. 
The solulion of caoutchouc in some of the 
oils has been used as a varnish, to render 
flexible substances, as silk, &c. impermeable 
to water or air. It has the advantage of 
being perfectly flexible ; but it is long be- 
fore it dries, and is liable to be softened by a 
very moderate heat. To render it less vis- 
cid, it is generally prepared from a mixture 
of volatile and expressed oils. 
CAP of maintenance, one of the regalia, or 
ornaments of state, belonging to the kings 
of England, before whom it was carried at 
the coronution, and other great solemnities. 
Caps of maintenance are also carried before 
the mayors of several cities in England. 
It is of crimson velvet, faced with ermine, 
and was formerly esteemed a badge and sym- 
bol of dignity, and suitable tota prince of 
the blood, being worn by King Edward 
III. and succeeding sovereigns down to 
Edward VI. ; but of late it has been grant- 
ed to private families. It is frequently to 
be met with above the helmet, instead of a 
wreath, under gentlemen’s crests. 
Cap, in a ship, a square piece of timber 
put over the head or upper end of any mast, 
having a round hole to receive the mast. 
By means of these caps the top-masts and 
top-gallant-masts are kept steady and firm in 
the tressel-trees where tlieir feet stand. 
Cap of a gun, a piece of lead which is put 
over a touch-hole of a gun to keep the prim- 
ing from being wasted or spoiled. 
CAPACITY, in a general sense, an apti- 
tude or disposition to retain or hold any 
thing. 
Capacity, in geometry, is the solid con- 
tents of any body; also our hollow measures 
